Altaire Performance Paper

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Altaire Performance Paper

  1. 1. November 2004 Performance MR A Hitachi Medical Systems America Publication THE THIRD WAY: HIGH-FIELD OPEN MR IMAGING WITH THE ALTAIRE® VASCULAR IMAGING DIAGNOSTIC NEURORADIOLOGY BREAST IMAGING MUSCULOSKELETAL TECHNIQUES
  2. 2. PerformanceMR THE THIRD WAY: HIGH-FIELD OPEN MR IMAGING WITH THE ALTAIRE® 5 Introduction: High-field open MR imaging with the Altaire 7 MR angiography with the Altaire high-field open MR system Gen J. Maruyama, MD Mary Moncilovich-Greer, RT(R)(MR), CRT Anthony Stauffer, MD 16 Diagnostic neuroradiology with the Altaire high-field open MR system C. Douglas Phillips, MD 27 Breast imaging with the Altaire high-field open MR system Hugo E. Isuani, MD 35 Musculoskeletal techniques and studies with the Altaire high-field open MR system Gen J. Maruyama, MD 43 Glossary of abbreviations A Hitachi Medical Systems America Publication
  3. 3. The third way: High-field open MR imaging with the Altaire® Contributors and institutions Gen J. Maruyama, MD Mission Regional Imaging Center provides magnetic-resonance Director, Musculoskeletal Imaging imaging services for Mission Hospital Medical Center, a regional pediatric-care facility serving a broad range of patients. A member Mary Moncilovich-Greer, RT(R)(MR), CRT of the St. Joseph healthcare family, Mission Hospital is the largest Lead MRI Technologist medical center in south Orange County and the area’s designated Anthony Stauffer, MD trauma center. Director, Neuroimaging Mission Regional Imaging Center Mission Viejo, California C. Douglas Phillips, MD The University of Virginia Health System embodies the leadership Professor of Radiology and inventiveness personified by its founder, Thomas Jefferson. The busy Chief of Diagnostic Neuroradiology multispecialty tertiary-care health system includes a large neurosciences staff, University of Virginia Health Sciences Center and the 600-bed hospital is a major mid-Atlantic referral site in neurosurgical, Charlottesville, Virginia craniofacial, and otolaryngological care. There is an active neuroradiologic training program, with diagnostic and interventional and neuroradiology fellows. Hugo E. Isuani, MD TotalCare is a service of Sierra Medical Center. Opened in 1976 at Staff Radiologist the foot of the Rocky Mountains, Sierra Medical Center is a 365-bed Sierra–Providence–TotalCare Network acute-care hospital providing advanced healthcare services not only to El Paso, Texas El Paso but also to the outlying communities of west Texas, to southern New Mexico, and to northern Mexico. ©2004 Hitachi Medical Systems America, Inc. 4 A Hitachi Medical Systems America publication
  4. 4. Introduction: High-field open MR imaging with the Altaire® Introduction: America, Inc., Twinsburg, Ohio). The Altaire has one of the highest field strengths High-field open MR imaging achieved to date for open MR (0.7 T), and it incorporates an extremely refined noise- with the Altaire® reduction technology. Further, the Altaire is designed with a high-performance gradient subsystem, which yields optimal spatial and contrast resolution and supports advanced imaging applications. Among the practical consequences are shorter repetition time (TR) selections and a reduction in time to echo (TE), minimizing dephasing and Background Historically, the status of open MR systems increasing T1 contrast. has been challenged by the theoretical Open magnetic resonance (MR) imaging correlation of magnetic field strength with Primer: The physics is well established as an alternative for signal-to-noise ratio (SNR). Of the three the increasing number of patients who are of the Altaire basic characteristics of an MR image — unable or unwilling to undergo tube-type The Altaire technology — known as contrast, SNR, and spatial resolution — closed MR imaging and for the radiologists “vertical-field with optimized subsystem it is the SNR that is the measure for the and technologists who want direct access integration” (VOSI) — employs noise overall quality of the image. The SNR for visual and auditory patient monitoring. reduction and enhanced RF signal detection increases with increases in the strength In contemporary diagnostic imaging, to improve SNR and thus yield images of the main magnetic field — almost high-field open MR systems, having comparable in quality to those from closed quadratically at lower field strengths, advanced right along with closed systems MR systems. linearly at higher field strengths. In the in terms of their capabilities, are being past, engineering challenges dictated the effectively used in regular rotation with An integral part of any MR system is its RF tunnel shape for maximum homogeneity and those closed systems for most imaging subsystem for delivering the excitation pulse efficiency, resulting in designs that restrict situations — brain disorders, traumatic and receiving the MR signal from the tissue access. Early attempts to provide greater injuries, eye abnormalities, spine diseases, by means of coils functioning as near-field patient comfort and surgeon access with tumor detection, liver and other abdominal antennae. Employing a vertical quadrature an open MR design had field strengths diseases, knee and shoulder injuries, facial/ (circularly polarized) solenoid design for <0.3 T. Since that time, innovative concepts neck abnormalities, cardiac malformations, its volumetric coils (Figure 1, page 6), the in superconducting magnet design have blood flow and vessel disorders. In these Altaire realizes an increase of 40% more yielded higher field strengths for open MR situations, high-field open MR systems SNR compared to systems with conventional systems, and the manufacturers of open deliver comparable image quality in coils. As a general rule, the smaller the coil systems have also increased SNR by refining comparable scan times for comparable and the closer it is to the patient — that is, RF systems and coil technology, deploying patient throughput. the better the coil fill factor, the relationship advanced pulse sequences consistent of the receiver’s coil size to the size of The best high-field open MR systems offer with those of tunnel type systems, and the object being imaged — the higher the state-of-the-art imaging techniques: implementing modifications in imaging SNR. By incorporating a wide range of • Long echo train fast spin echo for parameters that accentuate the strengths anatomically specific coils, the Altaire takes fast T2 imaging of the open MR paradigm. advantage of this higher SNR. • Echo-planar imaging (EPI) The leading open MR systems that In general, narrowing the bandwidth reduces • Diffusion-weighted imaging are now realizing the benefits of these the amount of noise sampled relative to useful in neurological diagnosis research directions may best be viewed the signal, thereby increasing SNR. The • Time-of-flight, phase contrast, and as representing a totally new MR system Altaire uses a variable bandwidth setting, contrast-enhanced MR angiography for concept — a third way — combining which provides an important “power-tool” advanced vascular studies advantages previously possessed separately parameter for adjusting image quality • Radiofrequency (RF) fat saturation for by conventional low-field open systems and without the chemical shift artifacts that enhanced visualization of musculoskeletal high-field closed systems. The advance is result from the use of narrower bandwidths pathology exemplified by the Altaire high-field open in 1.5 T high-field closed systems. MR system (Hitachi Medical Systems A Hitachi Medical Systems America publication 5
  5. 5. The third way: High-field open MR imaging with the Altaire® The Altaire VOSI technology also incorporates a high-performance gradient subsystem such as is found on high-field closed MR systems. In order to perform the newer techniques such as EPI that have revolutionized MR imaging, it is important to have both high gradient amplitude and high gradient slew rates.The maximum gradient strength of the Altaire is 22 mT/m, much higher than the gradient strengths of previous open MR systems and comparable to the gradient strengths of high-field closed MR systems. Moreover, the maximum slew rate of the Altaire — the ratio of gradient strength to rise time — is 55 T/m/s, much higher than the slew rates of previous open MR systems and comparable to the slew rates of closed MR systems. As with all advanced MR imagers, the Altaire uses various fast-scan and MR signal-data-management techniques that speed image acquisition — including fast spin-echo imaging, EPI, and partial k-space techniques that enable reduction in scan time with no loss of resolution. The articles in this monograph demonstrate the quality and versatility of the imaging that the VOSI features make possible when the Altaire is utilized as part of the regular scanner rotation in a variety of diagnostic areas — vascular imaging, diagnostic neuroradiology, breast imaging, and musculoskeletal imaging. Figure 1. The vertical-field orientation of the Altaire enables the use of solenoid radiofrequency coils instead of the less efficient saddle-type coils usually employed in horizontal-field systems. In order to maximize detection of transverse magnetization, the orientation of the receiving coil must be perpendicular to that of the main magnetic field. With horizontal-field systems, because the long axis of the patient is parallel to the magnetic field, it is often not possible to use the solenoid coils in volume (as opposed to surface) applications, with the coil completely enclosing the anatomical region. With this limitation overcome in the Altaire vertical-field system, volumetric application of solenoid coils can increase signal-to-noise ratio and produce an image quality that surpasses expectations for a field strength of 0.7 T. 6 A Hitachi Medical Systems America publication
  6. 6. Maruyama / Moncilovich-Greer / Stauffer MR angiography with the Altaire® high-field open MR system MR angiography with the Altaire® The volume acquisition of 3D TOF MRA (slabs up to 6 cm thick) makes for a higher high-field open MR system signal-to-noise ratio (SNR) than 2D TOF, and the ability to partition the slab into slices Gen J. Maruyama, MD less than 1 mm thick yields higher spatial resolution.1,3 Volume rendering increases Director, Musculoskeletal Imaging sensitivity for detection of small intracranial aneurysms.8,9 3D TOF has been improved Mary Moncilovich-Greer, RT(R)(MR), CRT with the hybrid technique of multiple Lead MRI Technologist overlapping thin slab acquisition.1,3 The drawback associated with the 3D TOF slab Anthony Stauffer, MD thickness is a more limited area of coverage. Director, Neuroimaging In addition, motion during the sequence will affect the entire slab rather than just an Mission Regional Imaging Center individual slice. Mission Viejo, California Contrast enhancement is a further advance for MRA. Whereas TOF MRA depicts MR angiography thus become saturated and produce little blood inflow, contrast-enhanced (CE) MRA MR signal. Since the blood is moving, these (CEMRA) is based on the reduction of the Imaging of the vascular system has T1 relaxation time of blood relative to spins are continuously flowing out of the changed dramatically over the past decade surrounding tissues following the rapid slice or slab and are replaced by fresh, fully as catheter-based angiography has been bolus injection of a paramagnetic contrast magnetized blood spins that produce a high replaced for many purposes by the rapidly agent (a gadolinium chelate). When MR MR signal and have not been saturated by advancing, less invasive modalities of signals are collected with a short TR value, the applied RF pulse.1-3 These magnetized ultrasound, computerized tomography, and the signal from the tissue surrounding the blood spins are then used to create the MRA magnetic resonance (MR) imaging.1-4 MR blood vessels is very small relative to that image. angiography (MRA) is often the procedure of the CE blood due to its longer T1 value.4 of choice for initial noninvasive assessment Once a series of 2D slices or a 3D slab has Because the veins enhance shortly after the of the intracranial vasculature.5,6 Now been acquired, the slices can be stacked arteries and shortly thereafter the contrast advances in high-field open MR have and processed for image display in an diffuses into the adjacent soft tissues, allowed performance of high-quality angiographic format.1,3 To date, the most successful use of contrast enhancement peripheral MRA, once reserved for high-field commonly employed projection techniques requires very fast data acquisition closed MR. for this purpose have been the maximum sequences.3 With a TR <10 milliseconds, intensity projection (MIP) algorithm and Available for years, and based on flow- it is possible to complete some CEMRA multiplanar reformations. The MIP technique related enhancement that distinguishes sequences within the span of a single has been enhanced by the volume-rendering moving from stationary spins, time-of-flight breath-hold (~30 seconds), thereby avoiding algorithm, which incorporates the entire (TOF) MRA is performed with either spin- respiratory motion.1,2 In CEMRA, the time data set into a 3D image — thus making it echo or gradient-echo pulse sequences. to the echo (TE) is kept at a minimum (~1 possible to visualize the vascular surface TOF MRA can be performed as a two- millisecond) in order to eliminate dephasing and intravascular details while preserving dimensional (2D) or three-dimensional (3D) artifacts and minimize T2 decay.2 It is spatial relationships.7 acquisition. The 2D acquisition collects frequently possible with CEMRA to image information from a thin slice of tissue while With 2D TOF MRA, it is possible to obtain lesions not visualized with noncontrast MRA. 3D acquisition collects information from a images of blood flow over large areas The following sections detail four slab of tissue. (common carotid arteries, pelvis, lower protocols for CEMRA that we have had extremities) in overall scan times of 5 to In the more frequently utilized gradient-echo success with as performed on an Altaire 10 minutes, depending on the number of “bright-blood” method, the stationary spins 0.7 T high-field open magnet. Our standard slices.1,2 However, resolution is limited by (vessel wall and surrounding soft-tissue protocols for CEMRA are listed. All patients the usual minimum slice thickness of about structures) in a slice or slab receive multiple are connected to our power injector via a 1.5 mm,3 and signal may not be adequate to radiofrequency (RF) pulses within a very 60-inch-length OPTISTAR Y tubing and a allow diagnosis in tortuous vessels.2 short repetition time (TR) (T1 weighting) and right antecubital 20G angiocatheter in order A Hitachi Medical Systems America publication 7
  7. 7. The third way: High-field open MR imaging with the Altaire® to help standardize injection times. K space is Figure 1 shows coronal-plane images of the carotid acquired in ADA format (3/4 K-space acquisition). arteries of a 72-year-old patient who presented with Injection rates for gadolinium and saline flush are a single episode of confusion. CEMRA of the carotid set at 2 cc per second. arteries was performed, using the Altaire high-field open MR system and protocol 1. A high-grade MRA of the stenosis was seen 2 cm distal to the left common carotid origin. carotid arteries A major application of MRA is screening the carotid arteries for arteriosclerotic disease. A common Protocol 1 source of transient ischemic attacks and stroke is atheromatous disease at the carotid bifurcation in Phased array neurovascular coil the neck, which has been imaged primarily using 2D FOV: 230-260 mm (to cover from proximal arch TOF, 3D TOF, and CEMRA in addition to ultrasound, to circle of Willis). computed tomographic (CT) angiography, and conventional angiography. With MR, 2D TOF may Sequence 1: Scanogram or scout of neck and offer the best edge definition and sensitivity to slow routine 2D TOF of carotids. blood flow, but its dependability is often limited Sequence 2: Test injection performed using by flow voids, susceptibility to artifacts based on dynamic 2D coronal RF spoiled SARGE (RSSG) patient movement, and signal loss along horizontal of neck. Record time when contrast enters portions of a vessel or along tortuous vessels. When into the proximal common carotid arteries. CEMRA is performed of the carotids, a 3D spoiled Injection rate: 2 cc gadolinium @ 2 cc per gradient-echo technique is used. A limitation of second with 20 cc saline flush. 3D CEMRA is the loss of edge definition and an apparent decrease in lumen diameter in both Sequence 3: Add 3 to 5 seconds to the time diseased and nondiseased areas.10 recorded during the test injection and use this value as the contrast transit time (ctt)/time delay before imaging begins. Perform a mask run prior to contrast and two consecutive postcontrast 3D coronal RSSG CEMRA runs. Injection rate: 20 cc gadolinium @ 2 cc per second with 20 cc saline flush. Figure 1. Coronal-plane images of the carotid arteries Figure 1A Figure 1B of a 72-year-old patient who presented with a single episode of confusion. Contrast- enhanced (CE) MRA of the carotid arteries was performed (see Protocol 1). Figure 1A is a maximum intensity projection from the CEMRA; the image in Figure 1B was processed with the volume-rendering algorithm. The arrow in each image indicates changes in keeping with a high-grade stenosis of the proximal left common carotid artery, approximately 2 cm from its origin. 8 A Hitachi Medical Systems America publication
  8. 8. Maruyama / Moncilovich-Greer / Stauffer MR angiography with the Altaire® high-field open MR system MRA of the thoracic aorta Protocol 2 CEMRA is being used increasingly instead of digital subtraction angiography (DSA) for first-line imaging CTL phased array coil, wrap quadrature coil, of the thoracic aorta in nontraumatic patients or in or peripheral vascular phased array coil can be patients unable to undergo CT angiography. Diverse used based on patient anatomy. pathology including aortic dissection, aneurysm, FOV: 300 mm intramural hematoma, stenosis, and congenital Sequence 1: Coronal localizer of thorax. abnormalities can be evaluated. The advances in gradient strength, making possible shorter TR Sequence 2: Axial T2 gradient echo of thorax and acquisition times, have allowed CEMRA to be used as scout to identify flow in aorta. implemented with subsecond temporal resolution,11 Sequence 3: Test injection performed using which is useful for evaluating high-flow vascular dynamic 2D coronal RSSG at the apex of the lesions such as shunts and dissections. Patient aortic arch off of sequence 2. Record time when positioning for MRA of the thoracic aorta is similar contrast reaches aortic arch. Injection rate: to positioning for MR imaging of the chest, and 2 cc gadolinium @ 2 cc per second with 20 cc these patients generally have MR imaging of the saline flush. chest along with the MRA study. Sequence 4: Add 5 to 7 seconds to the time Figure 2 shows sagittal-plane images from a recorded during the test injection and use CEMRA of a normal thoracic aorta. Figure 3 (page this value as the contrast transit time (ctt)/ 10) shows a type III descending thoracic aortic time delay before imaging begins. Perform a dissection. In each case, CEMRA was performed mask run prior to contrast and two or three on the Altaire high-field open MR system utilizing consecutive postcontrast coronal or oblique protocol 2. sagittal 3D coronal RSSG CEMRA runs. Injection rate: 30 to 35 cc gadolinium @ 2 cc per second with 20 cc saline flush. Figure 2. Sagittal-plane images Figure 2A Figure 2B of a normal thoracic aorta in a 45-year-old patient who presented with chest pain. Contrast-enhanced (CE) MRA was performed (see Protocol 2). Figure 2A is a maximum intensity projection from the CEMRA; the image in Figure 2B was processed with the volume-rendering algorithm. The images clearly show a normal ascending aorta, aortic arch, and descending thoracic aorta. A Hitachi Medical Systems America publication 9
  9. 9. The third way: High-field open MR imaging with the Altaire® Figure 3. Sagittal-plane images of the thoracic aorta Figure 3A Figure 3B of a 61-year-old patient with a sca sca history of thoracic aneurysm. Contrast-enhanced MRA was performed (see Protocol 2). Figures 3A and 3B are maximum intensity projections; the images in Figures 3C and 3D were processed with the volume-rendering algorithm. The images show ectasia tl tl of the ascending aorta and extensive type III dissection of the thoracic aorta. The proximal portion of this dissection is immediately distal to the takeoff of the left subclavian artery (sca). There Figure 3C Figure 3D sca sca is a small true lumen (tl) with delayed filling of the false lumen (fl). fl fl tl tl MRA of the renal arteries renal arteries from the aorta. The straight coronal or slight coronal oblique acquisition volume is placed Since its introduction, CEMRA has established itself with its anterior margin just anterior to the aorta as as a safe and reliable technique for detecting and a reference structure to ensure coverage of the left grading renal artery stenosis, with sensitivities renal vein. Typical slab thickness ranges from 60 to ranging from 91% to 100% and specificities ranging 100 mm. from 89% to 100%.2 Because of the lack of ionizing radiation and relatively low nephrotoxicity of Figure 4 shows coronal-plane images of the normal gadolinium at doses used for MRA, this technique is abdominal aorta and renal arteries of a 54-year- particularly attractive for the patient with a kidney old patient with a history of hypertension. Figure transplant or with renal failure and an elevated 5 shows a coronal-plane image of a 60-year-old creatinine level. patient with a history of elevated blood pressure and a right renal artery stenosis. In each case, Technical parameters for renal CEMRA are CEMRA was performed on the Altaire high-field similar to those for other abdominal CEMRA open MR system utilizing the T1-weighted gradient- studies. However, the imaging volume is placed echo technique in protocol 3. more posterior within the abdomen to cover the retroperitoneum and the expected course of the 10 A Hitachi Medical Systems America publication
  10. 10. Maruyama / Moncilovich-Greer / Stauffer MR angiography with the Altaire® high-field open MR system Figure 4. Coronal-plane images Protocol 3 Figure 4A of the normal abdominal aorta and renal arteries of Quadrature wrap coil or peripheral vascular a 54-year-old patient with phased array coil can be used. a history of hypertension. FOV: 300 mm Contrast-enhanced (CE) MRA was performed utilizing a 3D Sequence 1: Coronal Scanogram of abdomen. T1-weighted gradient-echo Sequence 2: T1 and T2 axial gradient-echo technique (see Protocol breath-hold (20 seconds) of abdomen. T2 axial 3). Figure 4A is a maximum intensity projection from the centered at the renal artery level. CEMRA; the image in Figure Sequence 3: Test injection performed using 4B was processed with the dynamic 2D coronal RSSG at the level of the volume-rendering algorithm. renal artery referenced from the T2 axial in The images show symmetric sequence 2. Injection rate: 2 cc gadolinium @ and normal perfusion of both 2 cc per second with 20 cc saline flush. Record kidneys and no evidence of Figure 4B renal artery stenosis. time when contrast reaches the aorta at the level of the renal artery. Sequence 4: Add 7 seconds to the time recorded during the test injection and use this value as the contrast transit time (ctt)/ time delay before imaging begins. Perform a mask run prior to contrast and two or three consecutive postcontrast coronal or oblique sagittal 3D coronal RSSG CEMRA runs. Injection rate: 30 to 35 cc gadolinium @ 2 cc per second with 20 cc saline flush. Figure 5. Coronal-plane image of the abdominal Figure 5 aorta and renal arteries of a 60-year-old patient with a history of elevated blood pressure. Contrast-enhanced MRA was performed utilizing a T1-weighted gradient-echo technique (see Protocol 3). The image, displayed using the maximum intensity projection algorithm, shows high-grade stenoses (arrows) near the origins of both the left and right renal arteries. A Hitachi Medical Systems America publication 11
  11. 11. The third way: High-field open MR imaging with the Altaire® MRA of the lower extremities the lower legs first, to minimize confounding venous flow, and then perform a two-stage CEMRA of the Peripheral vascular disease (PVD) is a common pelvis and thighs. Using this method, we have little condition with variable morbidity, affecting as many venous contamination of the entire peripheral run- as 10 million people in the United States. Most off. The Altaire table automatically steps between affected people are over 50 years12 and are also scan acquisitions. Screening peripheral MRA can at high risk of stroke, myocardial infarction, and identify which patients may need further catheter cardiovascular death.13 Imaging of PVD requires angiography/intervention. complete visualization of the vessels, from the origin of the renal arteries down to the distal Figure 6 shows a coronal-plane image of a normal arteries of the lower leg, in different projections. peripheral run-off study. Figure 7 (page 14) shows Previously the standard method for examining the a coronal-plane MRA of the lower extremities for vessels of the legs was intra-arterial DSA. More a 64-year-old patient with severe stenosis of the recently, with the introduction of new examination left femoral-popliteal graft anastamosis with the techniques — including fast scanning, CEMRA, popliteal artery. Occlusion of the left popliteal and automatic table movement14 — the use of 3D artery below the knee was present. Multifocal CEMRA has become practical. segmental stenosis of the right superficial femoral artery, anterior tibial artery, and tibioperoneal Prior to contrast injection, plain (mask) images trunk was also present. This patient subsequently are collected, and after an application of contrast obtained a catheter angiogram, confirming these agent, contrast images are acquired in precisely findings. In each case, CEMRA (40 cc gadolinium) the same positions and then subtracted from the was performed on an Altaire high-field open MR mask images in a manner similar to that used in system utilizing a peripheral vascular coil and a DSA. The scanning proceeds in two coronal steps T1-weighted spoiled gradient-echo technique, with from pelvis to ankle. However, at our center, we automatic table movement per protocol 4. reverse this order of imaging, acquiring images of Protocol 4 Second stage: Pelvis and thigh protocol Peripheral vascular phased array coil. Sequence 1: Use station A of four-station peripheral vascular coil. 3-plane Scanogram of pelvis. FOV: 400 mm Sequence 2: Table moves to station B, and obtain 3-plane Important to position legs in the coil by building up ankles so that Scanogram of thigh. legs are centered at the same height and are level. Sequence 3: Table moves back to station A. 3D coronal RSSG First stage: Lower leg protocol mask image obtained. Sequence 1: Lower leg (station C of peripheral vascular coil) Sequence 4: Table moves back to station B. 3D coronal RSSG 3-plane Scanogram. mask image obtained. Sequence 2: Axial T2 gradient echo to record flow in vessel from Sequence 5: Table moves back to station A. Subtract 2 seconds knee to ankle. from the test injection time obtained in sequence 3 of the first- Sequence 3: Test injection performed using dynamic 2D coronal stage lower-leg protocol, and use this value as the travel time for RSSG at the level of the popliteal artery as referenced from the pelvis (this step avoids the need for a repeat test injection). sequence 2. Injection rate: 2 to 3 cc gadolinium @ 2 cc per Perform a 3D coronal RSSG CEMRA of the pelvis and then the second with 20 cc saline flush. Record time when contrast reaches thigh during a two-stage contrast injection. Injection rate: 27 popliteal artery. cc gadolinium @ 2.5 cc per second, followed by 10 cc gadolinium @ 1.5 cc per second, followed by 40 cc saline flush @ 2.5 cc per Sequence 4: Add 7 seconds to the time recorded during the test second. injection and use this value as the contrast transit time (ctt)/time delay before imaging begins. Perform a mask run prior to contrast Sequence 6: During the injection, the table moves through station and two or three consecutive postcontrast 3D coronal RSSG B to obtain thigh CEMRA. CEMRA runs. Injection rate: 20 cc gadolinium @ 2 cc per second with 20 cc saline flush. 12 A Hitachi Medical Systems America publication
  12. 12. Maruyama / Moncilovich-Greer / Stauffer MR angiography with the Altaire® high-field open MR system Figure 6. Coronal-plane image of a normal Figure 6 peripheral run-off study of a middle-aged female. Contrast-enhanced MRA was performed utilizing a peripheral vascular coil and a T1-weighted spoiled gradient-echo technique, with automatic table movement and a biphasic injection of 20 cc and 10 cc gadolinium (see Protocol 4). The image is displayed using the maximum intensity projection algorithm. Dedicated peripheral vascular coil is fitted for peripheral run-off study utilizing the Altaire® high-field open MR system for contrast-enhanced MRA. The coil provides 141 cm of coverage, typically from the renal arteries to the feet. A Hitachi Medical Systems America publication 13
  13. 13. The third way: High-field open MR imaging with the Altaire® Figure 7A Figure 7B gr Figure 7C Figure 7D Figure 7. Coronal-plane MRA of the lower (SFA) was present. Multifocal segmental stenosis of extremities for a 64-year-old patient with severe the right SFA, anterior tibial artery, and tibioperoneal peripheral vascular disease. Figure 7A shows the trunk was also present. Contrast-enhanced MRA abdominal aorta at the level of the renal arteries was performed utilizing a peripheral vascular coil and aortic bifurcation. Figure 7B is at the level and a T1-weighted spoiled gradient-echo technique, of the iliac bifurcation; there is occlusion of the with automatic table movement (see Protocol 4). The left superficial femoral artery, with partial flow in images are displayed using the maximum intensity a femoral-popliteal bypass graft (gr). Figure 7C projection algorithm. This patient subsequently shows severe stenosis of the left femoral-popliteal obtained a catheter angiogram, confirming these graft anastamosis with the politeal artery (arrow). findings. Occlusion of the left mid superficial femoral artery 14 A Hitachi Medical Systems America publication
  14. 14. Maruyama / Moncilovich-Greer / Stauffer MR angiography with the Altaire® high-field open MR system References 9. Raaymakers TWM, Buys PC, Verbeeten B Jr, et al. MR angiography as a screening tool for intracranial 1. Roth CK. MRI: Rad Tech’s Guide to MRI: Imaging aneurysms: feasibility, test characteristics, and Procedures, Patient Care, and Safety. Malden, interobserver agreement. AJR. 1999;173:1469-1475. Mass: Blackwell Science; 2002. 10. Rapp JH, Saloner D. Current status of carotid 2. Montgomery ML, Case RS. Magnetic resonance imaging by MRA. Cardiovascular Surgery. imaging of the vascular system: a practical 2003;11:445-447. approach for the radiologist. Top Magn Reson 11. Finn JP, Baskaran V, Carr J, et al. Thorax: low- Imaging. 2003;14:376-385. dose contrast-enhanced three-dimensional MR 3. Bradley WG, ed. MR angiography. Applied angiography with subsecond temporal resolution— Imaging. 2000;1(3):1-4. initial results. Radiology. 2002;224:896-904. 4. Hornak JP. The basics of MRI. Accessed 12. Weitz JI, Byrne J, Clagett GP, et al. Diagnosis September 27, 2004, at http://www.cis.rit.edu/ and treatment of chronic arterial insufficiency of htbooks/mri. the lower extremities: a critical review. Circulation. 5. Barboriak DP, Provenzale JM. MR arteriography 1996;94:3026-3049. of intracranial circulation. AJR. 1998;171:1469-1478. 13. De Sanctis JT. Percutaneous interventions 6. Bhadelia RA, Bengoa F, Gesner L, et al. for lower extremity peripheral vascular disease. Efficacy of MR angiography in the detection Am Fam Physician. 2001;64:1965-1972. and characterization of occlusive disease in the 14. Ho KYJAM, Leiner T, de Haan MW, Kessels AGH, vertebrobasilar system. J Comput Assist Tomogr. Kitslaar PJEHM, van Engelshoven JMA. Peripheral 2001;25:458-465. vascular tree stenoses: evaluation with moving- 7. Mallouhi A, Felber S, Chemelli A, et al. Detection bed infusion-tracking MR angiography. Radiology. and characterization of intracranial aneurysms with 1998;206:683-692. MR angiography: comparison of volume-rendering and maximum-intensity-projection algorithms. AJR. 2003;180:55-64. 8. White PM, Teasdale EM, Wardlaw JM, Easton V. Intracranial aneurysms: CT angiography and MR angiography for detection — prospective blinded comparison in a large patient cohort. Radiology. 2001;219:739-749. A Hitachi Medical Systems America publication 15
  15. 15. The third way: High-field open MR imaging with the Altaire® Diagnostic neuroradiology with the closed systems — in a seamless manner, with little difference in patient throughput, Altaire® high-field open MR system and with basically indistinguishable results — allowing us to transparently meet the C. Douglas Phillips, MD high expectations of our referring specialists for diagnostic-quality images. Professor of Radiology Chief of Diagnostic Neuroradiology In some instances, our new or repeat University of Virginia Health Sciences Center patients insist on the comfort and convenience of the Altaire high-field open Charlottesville, Virginia system. In other cases, the Altaire is the only system that we can use because of patient size. As is true in many referral hospital practices, and increasingly in community practice, it is not unusual for us to be called on to image patients weighing Diagnostic neuroradiology scanners, equipped with high-performance gradient subsystems and anatomically well in excess of 300 pounds, patients with MR imaging at UVA whose girth prohibits their being imaged specific radiofrequency (RF) coils, we can The busy multispecialty tertiary-care health perform a full and up-to-date range of in a conventional closed MR system. In system at the University of Virginia (UVA) techniques and sequences — from more our experience, to deal with the growing includes a large neurosciences staff, and traditional T1-weighted and T2-weighted significant population of obese (and the 600-bed hospital is a major mid-Atlantic images in different planes, with and without morbidly obese) patients, it is essential referral site in neurosurgical, craniofacial, contrast, to gradient-echo and fast spin-echo to have a high-quality open scanner. MR and otolaryngological care. There is an techniques, inversion recovery sequences, imaging is not otherwise possible for these active neuroradiology training program, with diffusion-weighted imaging (DWI), balanced patients, and that must be a patient-care diagnostic and interventional neuroradiology SARGE (BASG), MR angiography (MRA), and consideration. fellows. We perform all diagnostic other innovative sequences. In the following sections, I describe in neuroradiologic examinations, such as Since September 2003, we have been general terms our standard protocols for computed tomography (CT), magnetic using the 0.7 T Altaire high-field open imaging of the brain, the cervical spine, and resonance (MR) imaging, diagnostic MR system (Hitachi Medical Systems the lumbar spine. In association with each cerebral angiography, myelography, and America, Inc., Twinsburg, Ohio) in regular of these areas, our special protocols for percutaneous biopsy procedures of the head rotation with our conventional high-field various indications are described, exemplary and neck, skull base, and spinal column. closed scanners ranging up to 1.5 T in field resultant images from the Altaire high-field The indications for MR imaging of the brain strength — for a broad range of primary open MR system are displayed, and our and spine are wide ranging and include back and follow-up imaging for brain tumors, findings in the cases represented by those and neck pain, radicular pain, recent spine strokes, spinal injuries, spinal degerative images are summarized. or joint injury, headaches, dizziness, stroke, disease, other neurosurgery patients, the evaluation of primary CNS neoplasms, and for initial evaluations and follow- metastatic disease, arteriovenous up examinations for a large number of malformations (AVMs), and a broad list of neurologic conditions. With some exceptions neurological disorders including movement such as MR spectroscopy, and research disorders, neurodegenerative conditions, and studies already in progress and mandating multiple sclerosis (MS). Working with UVA high-field imaging, the majority of our work neurologists, neurosurgeons, and others, we is not prioritized for a particular scanner but regularly identify multiple brain tumor types is assigned to whatever system is available as well as vascular and infectious disease, when the patient is scheduled. The Altaire cervical and lumbar disc herniations, high-field open system has been easily intrinsic spinal cord disease, and other and successfully customized for our site conditions, and we also monitor the status so that we can assign and perform exactly of many of these diseases through routine the same imaging sequences as on the follow-up examinations. With our MR 16 A Hitachi Medical Systems America publication
  16. 16. C. Douglas Phillips Diagnostic neuroradiology with the Altaire® high-field open MR system MR imaging of the brain CASE 1 Figure 1B with and without contrast Indication: Persistent headaches For our routine head imaging, after acquiring following head trauma. a three-axis scout image, we start with This elderly patient presented with headache a sagittal T1-weighted sequence, then associated with a fall 2 months previous, we follow with an axial fast spin-echo without a loss of consciousness. The patient T2 sequence, an axial FLAIR sequence, was referred for MRI imaging of the brain and then an axial or coronal T1 sequence. with and without contrast. The clinical Contrast is commonly indicated for MR suspicion of a significant but previously in a number of conditions and in a large unrecognized head injury was based on the number of clinical settings. For instance, persistent nature of the headaches. MR the routine evaluation of many patients has typically been utilized in the evaluation Figure 1B. Axial FLAIR (70-degree flip angle) with inflammatory, infectious, or known of more chronic manifestations of trauma, with driven equilibrium fast spin-echo neoplastic conditions mandates contrast while CT is more commonly utilized in the readout, 1-mm in-plane acquired resolution; administration. Patients of advanced age acute setting. slice position 5.5 mm superior to the image in being examined for often nonspecific Figure 1A; 14000/2300/112 (TR/TI/TE). indications commonly benefit from the inclusion of contrast-enhanced images. The Procedure increased incidence of tumors, both benign Precontrast sequences: Sagittal T1, Figure 1C and malignant, is the likely explanation. If axial T2, axial 2D gradient echo, axial FLAIR, the provided clinical indications mandate axial T1. contrast administration, we typically perform Postcontrast sequences: Axial T1, coronal three-plane postcontrast T1 images. We T1, sagittal T1; DWI with apparent diffusion utilize fat suppression if that is indicated coefficient (ADC) maps. for the anatomic area, such as the orbit or temporal bones, that we are studying. Common indications for our inclusion of fat-suppressed T1 images include detailed Figure 1A evaluation of the central skull base, orbits, temporal bones, and extracranial head and neck. Fat suppression is also useful in the Figure 1C. Axial T2 acquired in 2 min 35 evaluation of postoperative spines. sec with driven equilibrium fast spin-echo readout; image enhanced with 512x512 reconstruction; 6094/112 (TR/TE). Figure 1D Figure 1A. Axial FLAIR (70-degree flip angle) with driven equilibrium fast spin-echo readout, 1-mm in-plane acquired resolution; 14000/2300/112 (TR/TI/TE). Figure 1D. Axial T2 acquired in 2 min 35 sec with driven equilibrium fast spin-echo readout; slice position 5.5 mm superior to the image in Figure 1C; image enhanced with 512x512 reconstruction; 6094/112 (TR/TE). A Hitachi Medical Systems America publication 17
  17. 17. The third way: High-field open MR imaging with the Altaire® Figure 1E Figure 1H Case 1 findings The brain parenchyma was within normal limits, and there was no abnormal contrast enhancement. The ventricles were normal. There were no extra-axial collections. The paranasal sinuses and orbits are within normal limits. The gradient-echo sequences demonstrated no evidence of blood products within the brain that would be suggestive of chronic blood-degradation products that might accompany significant head injury. Figure 1E. Axial T2 acquired in 2 min 35 Figure 1H. Postcontrast axial spin-echo T1; Impression: Normal MR examination sec with driven equilibrium fast spin-echo contrast enhanced with MTC pulse; slice of the brain. readout; slice position 11 mm superior to the position 11 mm superior to image in Figure image in Figure 1C; image enhanced with 1F; 550/13 (TR/TE). 512x512 reconstruction; 6094/112 (TR/TE). Figure 1F Figure 1I Figure 1F. Postcontrast axial spin-echo T1; Figure 1I. Postcontrast sagittal T1; contrast enhanced with MTC pulse; conventional fast spin-echo readout; 550/13 (TR/TE). 380/12 (TR/TE). Figure 1G Figure 1J Figure 1G. Postcontrast axial spin-echo T1; Figure 1J. Axial T2 gradient echo with contrast enhanced with MTC pulse; slice 25-degree flip angle; 600/33 (TR/TE). position 5.5 mm superior to the image in Figure 1F; 550/13 (TR/TE). 18 A Hitachi Medical Systems America publication
  18. 18. C. Douglas Phillips Diagnostic neuroradiology with the Altaire® high-field open MR system CASE 2 Figure 2A Figure 2D Indication: Tumor follow- up — the patient had undergone chemotherapy and radiation therapy for known metastatic involvement of the brain by nongestational trophoblastic disease. This young female patient with a nongestational trophoblastic tumor metastatic to the brain underwent MR examination 18 days previous. The follow-up MR imaging of the brain with and without Figure 2A. Axial T2 with driven equilibrium Figure 2D. Postcontrast axial T1 at same contrast was performed due to a recent fast spin-echo readout; image enhanced with location as the image in Figure 2C; lesion alteration in sensorium following radiation 512x512 reconstruction; 6602/112 (TR/TE). enhancement maximized with combination therapy. Follow-up of patients undergoing of gadolinium and MTC; 586/13 (TR/TE). treatment of CNS neoplasms, both primary and metastatic to the brain, is a large Figure 2B volume of our practice. These patients may undergo more traditional chemotherapy regimens or conventional external beam Case 2 findings radiation therapy; alternatively, they may undergo more novel therapies, including The examination again demonstrated a large focused gamma radiation (Gamma Knife), mass centered in the right temporal lobe. tumor vaccine therapy, intra-arterial This large metastatic lesion had minimally chemotherapies, and other innovative increased in size. However, there had been therapies for tumor treatment. These the development of an overall increase in patients require high-quality imaging in their the heterogeneous enhancement as well as evaluation and follow-up, and consistency of increased surrounding edema. Further, two the imaging procedures across a number of Figure 2B. Axial T2 FLAIR with driven small metastases in the right frontal lobe platforms is very important. equilibrium fast spin-echo readout; echo had enlarged and were more prominent. The factor of 16 contributes to short scan time; degree of midline shift had not significantly 14000/2300/112 (TR/TI/TE). changed. No new lesions were identified. Procedure Presumed postoperative leptomeningeal Precontrast sequences: Axial T2 enhancement was again noted overlying the weighted, axial FLAIR, axial T1 weighted. Figure 2C tumor. Postoperative changes in the right temporal cranium are also again noted. The Postcontrast sequences: Axial T1 right mastoid air cells remained opacified. weighted, sagittal T1 weighted, coronal T1 weighted; DWI. Impression: • Although only minimally changed in size, the large right temporal lobe mass demonstrated increased heterogeneous enhancement and surrounding edema. • The small right frontal lobe metastases had slightly enlarged in the interval. Figure 2C. Precontrast axial T1 with MTC; 583/13 (TR/TE). A Hitachi Medical Systems America publication 19
  19. 19. The third way: High-field open MR imaging with the Altaire® CASE 3 Figure 3A Case 3 findings Indication: Suspected pituitary There was a 3.7-mm area of low T1 signal neoplasm — based on a number of within the left anterior-inferior pituitary hormonal abnormalities and pertinent gland that demonstrated diminished clinical history. enhancement compared with the rest of the gland on the postcontrast images. This 37-year-old female was diagnosed The lesion demonstrated hyperintense T2 with Forbes-Albright syndrome (ICD-9 signal. There was no evidence of cavernous 253.1) based on the finding of galactorrhea sinus involvement. The suprasellar cistern and amenorrhea and was referred for MR appeared normal. The pituitary infundibulum imaging of the brain with attention to the remained midline and normal in appearance. sella and the pituitary gland. A number of Figure 3A. Precontrast coronal T1; There were no other significant findings, endocrine abnormalities suggested disease conventional spin-echo sequence with 3-mm such as hypothalamic abnormalities, and of the hypothalamic-pituitary axis, and the slice thickness and submillimeter in-plane there were no extra-axial fluid collections. diagnostic test of choice in these patients resolution; 350/17 (TR/TE). The appearance of the remainder of the CNS is high-resolution imaging of the pituitary structures were within normal limits. gland with MR. Our protocol consists of very thin-section coronal T1 and T2 images Impression: The findings were consistent Figure 3B through the sella turcica before contrast with microadenoma in the left anterior- administration, followed by thin-section T1 inferior pituitary gland. images in the coronal and sagittal planes. Our slice thickness for all of our imaging platforms is 3 mm. Optimally, these images are performed without an interslice gap but with traditional or fast 2D spin-echo techniques, a very thin interslice gap improves the overall image quality. Procedure Figure 3B. Postcontrast coronal T1; 350/17 Sella protocol: Sagittal and coronal (TR/TE); at the same slice location as the precontrast T1 weighted, sagittal and image in Figure 3A. coronal postcontrast T1 weighted, and coronal and axial T2 weighted. Figure 3C Figure 3C. Coronal T2 with driven equilibrium fast spin-echo readout for T2 weighting and fast acquisition time; 3-mm slice thickness; 4100/112 (TR/TE). 20 A Hitachi Medical Systems America publication
  20. 20. C. Douglas Phillips Diagnostic neuroradiology with the Altaire® high-field open MR system CASE 4 Figure 4A Figure 4C Indication: Follow-up MR examination of a vestibular schwannoma that had undergone prior Gamma Knife treatment. This middle-aged patient with a right vestibular schwannoma measuring 22 by 3 by 14 mm had undergone an MR examination 5 months previous, at which time the schwannoma had been targeted for focused radiation treatment with the Gamma Knife. The follow-up examination Figure 4A. Precontrast axial T1; high Figure 4C. Postcontrast coronal T1; was performed with and without contrast. resolution (0.6 mm in-plane); 3-mm slice 401/17 (TR/TE). thickness; image enhanced with 512x512 Our facility has a very active Gamma Knife reconstruction; 400/16 (TR/TE). program, with a large number of AVMs, benign and malignant primary brain tumors, and vestibular schwannomas treated over Case 4 findings Figure 4B the years. The findings of successfully treated schwannomas include diminished The examination demonstrated a right central enhancement and decrease in internal auditory canal lesion with extension tumor size over time. The first follow-up into the cerebellopontine angle, which had examination may demonstrate a slight slightly increased in size in the interval. increase in tumor size, perhaps reflecting The enhancement pattern was fairly typical some tumor edema. We commonly perform for post-treatment schwannomas, with follow-up MR examinations in these patients peripheral enhancement and a low signal at 6 months following therapy and on a intensity center, and it was approximately yearly basis after the lesion has become 1 mm greater in diameter than on the stable in size and appearance. The results previous examination. Mass effect upon the following Gamma Knife therapy compare Figure 4B. Postcontrast axial T1 with cerebellar peduncle was noted; however, favorably with surgical figures, and this radiofrequency fat saturation, at same there was no radiation change in the treatment modality has gained increased position as the image in Figure 4A; adjacent parenchyma. No other lesions acceptance for a wide range of patients, 350/15 (TR/TE). were identified. There was no evidence notably those who are poor surgical of hemorrhage. candidates or who have lost considerable Impression: Since the previous exami- hearing. nation, there was minimal enlargement of the right vestibular schwannoma, with Procedure findings representative of the Gamma Knife therapy. Precontrast sequences: Sagittal T1 weighted, axial T2 weighted, axial T1 weighted. Postcontrast sequences (fat saturation): Axial T1 weighted, coronal T1 weighted; 3D balanced SARGE (BASG) with axial reconstructions. A Hitachi Medical Systems America publication 21
  21. 21. The third way: High-field open MR imaging with the Altaire® CASE 5 Figure 5A Case 5 findings Indication: Headaches, The cerebellar tonsils extended at least 6 mm occasional gait disturbances, below the level of the foramen magnum, and blurred vision. resulting in relative “crowding” of the tonsils and brainstem and a relative paucity of This 40-year-old patient presented with the cerebrospinal fluid (CSF) spaces. There some relatively nonspecific neurologic was no evidence of a syrinx within the symptoms and blurred vision (ICD-9 368.8) visualized portion of the upper cervical cord. and was subsequently referred for MR There was no hydrocephalus. The signal imaging of the brain with and without and configuration of the brain substance contrast. With these nonspecific neurologic was otherwise normal. There was no mass symptoms, this patient was referred Figure 5A. Sagittal T1 with fast spin-echo effect or space-occupying lesion and no for cranial MR imaging to investigate a readout; image enhanced with 512x512 evidence of hemorrhage. The remaining number of possible etiologies. Nonspecific reconstruction; 420/12 (TR/TE). CSF-containing spaces were normal. There neurologic symptoms can be the most was no evidence of restricted diffusion on difficult problems for the clinician to the diffusion-weighted images. No signal investigate, and MR, being the most Figure 5B abnormalities were demonstrated after sensitive examination for evaluating intravenous contrast administration. Mild the brain, is the most frequently utilized inflammatory changes were noted within diagnostic test. While more specific the frontal sinuses and bilateral anterior neurologic symptoms may lead to a more ethmoid air cells. detailed and specific examination, it is still useful to have a protocol for the overall Impression: evaluation of the entirety of the brain in a • The crowding of the foramen magnum thorough and expeditious fashion. In this with inferior displacement of the case, the clinical suspicion was actually that cerebellar tonsils 6 mm below the foramen of a demyelinating disease, such as MS, and was compatible with the diagnosis of the examination was tailored to exclude MS Arnold-Chiari type I malformation. as a primary consideration. Figure 5B. Axial T2 with driven equilibrium • There was no evidence of demyelinating fast spin-echo readout; image enhanced with disease. Procedure 512x512 reconstruction; 5078/112 (TR/TE). Precontrast sequences: Axial T1 weighted, axial T2 weighted, sagittal and Figure 5C axial FLAIR; axial DWI with ADC maps. Postcontrast sequences: Axial T1 weighted, coronal T1 weighted. Figure 5C. Axial T1 with MTC pulse; image enhanced with 512x512 reconstruction; 485/16 (TR/TE). 22 A Hitachi Medical Systems America publication
  22. 22. C. Douglas Phillips Diagnostic neuroradiology with the Altaire® high-field open MR system CASE 6 Figure 6A Case 6 findings Indication: Worsening gait No areas of restricted diffusion were instability in an elderly patient with identified to suggest an acute infarct. prior strokes. Increased signal was present within the superior left cerebellar hemisphere and in This elderly patient, with a history of the inferior right cerebellar hemisphere, cerebrovascular accident in the left consistent with encephalomalacia from the cerebellum in 1990, presented with old infarction. There was mild generalized progressive gait instability over the previous cortical atrophy. Minimal spotty bilateral 5 days (ICD-9 780.4) and was referred for white matter T2 signal abnormalities were MR imaging of the brain with and without present, likely due to chronic small-vessel contrast. The evaluation of patients who ischemic injury. The brain and brain stem have had the acute or subacute onset of new Figure 6A. Axial T2 with driven equilibrium fast spin-echo pulse sequence; image were otherwise normal in morphology and neurologic symptoms may suggest a cerebral enhanced with 512x512 reconstruction; signal characteristic. There were no masses infarction. This suspicion is increased with 6094/112 (TR/TE). and no extra-axial collections. There were increasing age or with the presence of normal flow voids in the major intracranial vascular risk factors. We typically view the vessels. There were no areas of abnormal evaluation of a stroke patient as a study not Figure 6B enhancement. No MRA was requested or only of the brain but also of the cerebral performed in this case. vasculature. This means the examination will typically be MR imaging of the brain and Impression: also MRA of the extracranial and intracranial • There was no evidence of acute infarction. vasculature. Obviously, this examination is tailored to the clinical suspicion and to other • There were multiple old cerebellar tests that may have already been performed. infarctions. Many clinicians request Doppler ultrasound of the carotid bifurcations as a primary diagnostic modality and perform MR imaging only of the brain. Figure 6B. Axial FLAIR with driven equilibrium Procedure fast spin-echo readout and reduced flip Precontrast sequences: Axial T1 angle; 14000/2300/112 (TR/TI/TE). weighted, axial T2 weighted, axial FLAIR; axial DWI. Figure 6C Postcontrast sequences: Axial T1 weighted, sagittal T1 weighted, coronal T1 weighted. Figure 6C. Postcontrast sagittal T1 with conventional fast spin-echo readout; 380/12 (TR/TE). A Hitachi Medical Systems America publication 23

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