DSA ITS APPLICATION AND ADVANCEMENT Moderator: MR. S.R.CHOWDHURY TUTOR, DEPT.OF RADIO-DIAGNOSIS & IMAGING, PGIMER CHANDIGARH Presented by: DEEPAK GUPTA BSc final year Student , DEPT.OF RADIO-DIAGNOSIS & IMAGING PGIMER CHANDIGARH
2/24/2010 2 ANGIO? ANGIO means blood vessel And angiography is the radiological study of blood vessel in the body after the introduction of iodinated contrast media. SUBTRACTION? It is simply a technique by which bone structures images are subtracted or canceled out from a film of bones plus opacified vessels, leaving an unobscured image of the vessels.
2/24/2010 3 WHAT DO YOU MEAN BY DSA DSA-The acquisition of digital fluoroscopic images combined with injection of contrast material and real-time subtraction of pre- and post contrast images to perform angiography is referred to as digital subtraction angiography
2/24/2010 4 HISTORY The Portuguese neurologist Egas Moniz,( Nobel Prize winner 1949), in 1927developed the technique of contrast x-ray cerebral angiography to diagnose diseases, such as tumors and arteriovenous malformations. The idea of subtraction images was first proposed by the Dutch radiologist Ziedses des Plantes in the 1935, when he was able to produce subtracted images using plain films. With the introduction of the Seldinger technique in 1953, the procedure became safer as no sharp devices need to remain inside the vascular lumen.
2/24/2010 5 HISTORICAL DEVELOPMENT CONVENTIONAL SUBTRACTION TECHNIQUE Photographic method used to eliminate unwanted images. No addition of information;only purpose to make diagnostically important information to see. First described by a Dutch radiologist, Zeides des Plantes, 1935. 3 conditions:SCOUT FILM ANGIOGRAM FILM-CONTRAST NO MOTION OF HEAD
2/24/2010 6 CONTD. The principles of subtraction are based on the following: The scout film shows the structural details of the skull and the adjacent soft tissue. Angiogram film shows exactly the same anatomic details, if the patient does not move, plus the opacified blood vessels. If all the information in the scout film could be subtracted from the angiogram film, only the opacified vessel pattern would remain visible.
2/24/2010 7 EQUIPMENT THE AOT CHANGER: Can change films –6/s or 1/5s Two of these changers can be coupled electronically and mechanically and will operate out of phase or synchronously with each other. Radiographs in 2 planes simultaneously-one mounted vertically and other horizontal.
2/24/2010 8 AOT CONTD. LOADING MAGZINE Large steel container. Inside the container are arranged a no. of strong wire separators. 30 sheets of film. Precautions :each film should slide into position by it’s own wt. RECIEVING / LOADING MAGZINE
2/24/2010 9 EXPOSURE AREA : Rectangular, slightly recessed area at the top of the changer. Defined by heavy metal frame. Within this is a secondary grid. Supported on 4 small helical springs placed cornerwise and to consist of a stout Al plate, to the lower side of which is attached an intensifying screen. 30 SEPERATING WIRES RECEIVING CASSETTE: Shallow,polished metal container. Lid is a sliding section in a side which can be pushed down by firm finger pressure and is retained by central spring loaded catch.
2/24/2010 10 THE ROLL FILM CHANGER: Mechanically easier to wind roll films. 12/s.
2/24/2010 11 DIGITAL SUBTRACTION ANGIOGRAPHY HISTORY: Developed in 1970s. University of Wisconsin, University of Arizona,University of Kiel. Commercial systems introduced in 1980.
2/24/2010 12 Angiography theory ages Single shot angiography Manual changer AOT PUCK DSA
2/24/2010 13 EQUIPMENT AND APPARATUS Both film and digital capabilities are usually present and the fluoroscopy equipment operates in the conventional way. Brief review : Light detected amplified Input surface Visible light Output phosphor Electrical signal Light intensity
2/24/2010 14 DIGITAL IMAGE PROCESSOR DISPLAY SECTION DIGITAL ARITHEMATIC UNIT DIGITIZER DIGITAL IMAGE MEMORY X-RAY CONTROL SIGNALS MONITOR COMPUTER MULTIFORMAT CAMERA DIGITAL DISK STORAGE
2/24/2010 15 X-Ray Unit Should be capable of rapid serial exp. @2-8 frames/sec for up to 20 sec. Near monochromatic beam consistent output. Isocentre motorized table ,tilt 90-0-90 , up-down, sliding ,floating capable Ceiling mounted C-arm with versatile movements II system with multi field ( 6”,9”,12”,16”) High resolution TV /CCD camera Computer with high definition monitor system
2/24/2010 16 Contd. High output preferably high frequency generator High heat loading capacity ,fast heat dissipation, high speed anode Target material tungsten,rhenium,graphite. Oil-water close loop cooling
2/24/2010 17 In our dept.Siemens polydoros SX 65-80 Polystar
2/24/2010 18 NECESSARY EQUIPMENT USED WITH ANGIO(DSA) GAS , AIR & VACUUM PORTS Boyle apparatus
2/24/2010 23 Modern DSA systems are based on digital fluoroscopy/fluorography systems, which are equipped with special software and display facilities. Digital subtraction angiography (DSA) was developed to improve vessel contrast. This is a technique that uses a computer to subtract two images, obtained before and after contrast media is injected into the vessels of interest. The anatomical structures that are the same in the two images can be removed and the resulting image shows the vessels only.
2/24/2010 24 The image before the contrast agent is administered is called the mask image. Once the contrast is administered, a sequence of images are taken by a television camera in analog form, which is then digitised by computer. The DSA processor has two separate image memories, one for the mask and the other for the images with contrast medium. These two image memories are subtracted from one another arithmetically, and the result goes to an image processing and display unit.
2/24/2010 25 IMAGE PROCESSING Adjust contrast & brightness. Remasking – correcting misregistered images. Pixel shifting. Edge enhancement – edges of the vessels can be enhanced so that small details can be made more obvious. Image zoom. land marking – a small amount of original image is added into the subtracted image. Noise smoothing – operates by reducing the statistical fluctuations in each pixel by averaging the pixel with it's closest neighbors. The visual prominence of noise has been suppressed by averaging, but resolution is decreased.
2/24/2010 26 Road Mapping Road mapping is useful for the placement of catheters and wires in complex and small vasculature. A DSA sequence is performed, and the frame with maximum vessel opacification is identified;this frame becomes the road map mask. The road map mask is subtracted from subsequent live fluoroscopic images to produce real-time subtracted fluoroscopic images overlaid on a static image of the vasculature
2/24/2010 27 When a digital subtraction technique is used, patient motion that occurs between acquisition of the precontrast images and acquisition of the postcontrast images will result in artifacts due to misregistration of the two images. If these arti-facts are observed, it is possible to reregister the pre- and postcontrast images by shifting the subtraction mask (precontrast image) with respect to the postcontrast image and resubtracting the two images
2/24/2010 29 Working principle of T.V monitor Control Grid Receive Video signal from ccu & regulate No. of e-ns & the brightness of individual dots Produce bright area in the TV Picture Grid cuts off the e-ns flow almost completely Dark Area E-ns is Accelerated Strikes the fluorescent Screen Emits large no. of light photons VISIBLE TV IMAGE
Resolution is the process by which something is separated into its component part
The resolution of imaging system refers to the amount of detail which is observable
It may be formulated as the number of pairs of black and white lines which an image forming or image recording device can demonstrate in a length of 1 mm
Vertical resolution is determined by no. of vertical scan lines (e.g. 625).
In recent years the manufactures of radio diagnostic imaging equipment have developed his definition TV system which employ 1249 or even more lines.
2/24/2010 35 Contrast The contrast of the image on a TV screen clearly depends on the contrast of the original image focused onto the signal plate of the pick up tube. Both camera and monitor affect the contrast of a TV image. A vidicon camera reduces contrast by a factor of approx. 0.8 and the monitor enhances by a factor of 2.
2/24/2010 36 Brightness The term luminance and brightness are often used when discussing the aspect of tv image Luminance can be defined as light emitted per unit area from a surface. It is measured in candela per square meter (cd/m2) Automatic brightness control (ABC)
ABC helps to maintain the image intensifier exposure rate based on the subject’s thickness
It is critical to the patient dose and image quality
2/24/2010 37 The ABC monitors the light output from an area of the face of the image intensifier and it tries to maintain the signal travel within an approximate range of that output and adjust tube potential (kvp) and tube current (mA) a/c to predefined algorithm It refers to control of x-ray exposure levels Automatic gain control (AGC) If brightness is controlled by varying sensitivity of the TV system the term AGC is used. It is fairly simple and inexpensive way to control image brightness It does not change the x-ray dose rate to the patient 37
2/24/2010 38 Image lag Lag is the term used to describe inability of an imaging system to follow rapid changes in its input image Distortion Distortion of the image occur in the image intensifier or in the optical coupling system which links its output phosphor to the signal plate of the TV pick up tube 38
2/24/2010 39 Artifacts Lag Vignetting, Veiling glare Pincushion distortion S distortion. 39
2/24/2010 40 Lag Lag is the persistence of luminescence after x-ray stimulation has been terminated. Lag degrades the temporal resolution of the dynamic image. Older imageintensifier tubes had phosphors with lag times on the order of 30–40 msec. Current imageintensifier tubes have lag times of approximately 1 msec. Vignetting A fall-off in brightness at the periphery of an image is called vignetting. Vignetting is caused by the unequal collection of light at the center of the imageintensifier compared with the light at its periphery. As a result, the center of an imageintensifier has better resolution, increased brightness, and less distortion. 40
2/24/2010 41 Veiling Glare Scattering of light and the defocusing of photoelectrons within the imageintensifier are called veiling glare. Veiling glare degrades object contrast at the output phosphor of the imageintensifier. As mentioned, the contrast ratio is a good measure of determining the veiling glare of an imageintensifier. X-ray, electron, and light scatter all contribute to veiling glare. Pincushion Distortion
Pincushion distortion is a geometric, nonlinear magnificationacross the image.
The magnification difference at the peripheryof the image results from the projection of the x-ray beam ontoa curved input surface.
The distortion is easily visualizedby imaging a rectangular grid with the fluoroscope.
2/24/2010 42 S DISTORTION Electrons within the imageintensifier move in paths along designated lines of flux. External electromagnetic sources affect electron paths at the perimeter of the imageintensifier more so than those nearer the center. This characteristic causes the image in a fluoroscopic system to distort with an S shape . Manufacturers include a highly conductive mu-metal shield that lines the canister in which the vacuum bottle is positioned to reduce the effect of S distortion. 42
Blood vessels are not normally seen in an x-ray image, because of low tissue contrast.
To increase image contrast, contrast agents, which are dense fluids with elements of high atomic numbers, such as iodine, are injected into a blood vessel during angiography. Because of its higher density and high atomic number, iodine absorbs photons more than blood and tissue.
This creates detailed images of the blood vessels in real time.
The first contrast media used for intravascular injection were called high-osmolar contrast media (HOCM). (osmolality is the measure of the particle concentration in a solution.)
2/24/2010 46 HOCM had osmolarity seven to eight times higher than plasma. This high osmolarity caused adverse effects such as pain, endothelial damage, thrombosis, and increased pressure in the pulmonary circulation. Low-osmolar contrast media (LOCM) were first developed in the 1970's and these helped to reduce these side effects. One of the major risks of modern iodine contrast media is an allergic reaction to iodine. 46
When the catheter is in the correct position, the wire is pulled out and dye is injected through the catheter.
Images are acquired during contrast injection. Injections can be made directly into the artery of interest (selective arteriography)
Complications from an arteriogram are very rare, but there is some risk. Most problems that occur can be detected at the time of the procedure or immediately after the procedure. The artery may be injured at the puncture site or along the artery where the catheter is passed.
2/24/2010 58 COMPLICATIONS 0.16% major complication rate. Local complications: hematoma, vessel laceration, dissection, peudoaneurysm, AV fistula. Systemic complications: contrast reactions, fever, sepsis, dehydration, death. CNS complication: aggravation of preexisting complaints, neurological deficit. 58
2/24/2010 59 POSTPROCEDURAL CARE After the catheter is removed compression is applied to the puncture site. The patient is asked for bed rest for a minimum of 4 hours During rest patient is monitored and vital sign like peripheral pulse like distal to Puncture are regularly The extremity is also checked for warmth, color, numbness to ensure circulation has not been disrupted.
2/24/2010 60 Oral fluid is given and analgesics are given if required. Special care should be given in case of children and geriatric patient since additional Patience is required. They have given warming blanket to keep the body temp. Normal. Geriatric patient also frequently feel nervous and afraid of falling off the Table ,reassurance and additional care from the technologist will enable the Patient to feel secure and comfortable.
2/24/2010 61 Digital subtraction techniques DSA has many techniques
Each subtracted image is the difference b/w the images separated by some fixed interval of time.
2/24/2010 67 Temporal filtering
Temporal filters are used.
This filter generates one final image by adding & subtracting some of the original images together, & then shifting & repeating to form the next image.
2/24/2010 68 ADVANCEMENTS IN OUR DEPARTMENT Philips Allura Xper FD 20/10 and interventional tools The Allura Xper FD20/10 is a biplane flat detector system with integrated 3D for intricate neurovascular procedures. Combining the proven stable geometry with 'real-time' Allura 3D- reconstructions, Xper CT, SPECTRA BEAM 3D Roadmapping, and multi-modality information integration,
2/24/2010 70 the Allura Xper FD20/10 balances superb image quality with excellent dose safety. The flat detector's unique distortion-free imaging chain redefines image clarity and captures information at a resolution four times greater than conventional X-ray systems.
2/24/2010 71 Xper ct With XperCT clinicians can access CT-like imaging right on the angio system so that they can assess soft tissue, bone structure and other body structures before, during or after an interventional procedure. The XperCT reconstruction is created from a rotational acquisition performed on the Allura Xper system. This reconstruction can be overlaid with the 3D vascular image. IT Bring 3D soft tissue imaging to your angio suite 3D soft tissue imaging supports diagnosis, planning, interventions and treatment follow-up, XperCT can be combined with Allura 3D-RA images to visualize soft tissue and vascular anatomy on one image. Using CT-like imaging for a post-procedural check can help reduce delays and improve patient comfort.
2/24/2010 72 XperCT overlay on both the internal carotid and vertebral arteries
2/24/2010 74 Spectra Beam It is basically a selectable copper beam filtration The combination of SpectraBeam with the MRC- tube allows increased X-ray output with better filtration of soft radiation. SpectraBeam offers filters of 200, 500 and 1000 microns thickness Cu equivalent to provide a high level of radiation protection regardless of the projection or patient absorption. This reduces patient X-ray dose for cardiac and vascular applications, while maintaining the same image quality.
2/24/2010 75 When the acquisition sequence is initiated, the C-arm rotates from left to right for 220o at 40o per second but data acquisition is accomplished at the range Of 200o, acquiring at 8.8 frames per second for 5 seconds resulting in 44mask images The gantry then rotates back to the starting position. When the C-arm returns to the starting position, the Power injector is initiated according to the injector delay protocol, which is Mask-to-Image delay of 1.1 seconds and Injector-to-Image delay of 1.1 seconds. The Power injector injects 18 milliliter of Visipaque 280 at the rate of 3.6 ml/second for Internal Carotid Artery (ICA). The gantry repeats the mask acquisition path and acquires another 44 images with contrast. Real time subtraction angiographs are displayed on post processing screen. 75 75
2/24/2010 77 Generator characteristics X-ray generators High powered x-ray generators to provide almost constant potential power supply to the tube. Two Velara CVFD microprocessor-controlled 100 kW high-frequency converter generators. Minimum exposure time of 1 ms. Voltage range: 40 kV to 125 kV. Max current: - MRC-GS 04-07: 802 mA at 80 kV. - MRC-GS 05-08: 1062.5 mA at 80 kV. Automatic kV and mA control for optimal image quality prior to run to reduce dose. 77 77
2/24/2010 78 78 Generator characteristics cont. Max continuous power for fluoroscopy: 2.4 kW for 0.5 hour and 2 kW for 8 hours. Nominal power (highest electrical power): 100 kW (1000 mA at 100 kV) Reference loading conditions: 110 kV, 18 mA continuous. Pulsed X-ray of 3.75, 7.5, 15 and 30 frames/sec. in monoplane and biplane mode for pulsed fluoroscopy. Pulsed X-ray of 0.5 to 6 frames/sec. for digital subtracted acquisition in monoplane and biplane mode. Pulsed X-ray up to 6 frames/sec. for digital acquisition in monoplane and biplane mode. 15 and 30 frames/sec. Noise < 55 dB(A). 78
2/24/2010 79 The high performance metal ceramic tubes . Most relevant feature is support of the rotor anode in a spiral groove bearing The spiral groove bearing glides on a thin film of liquid metal to maximize heat dissipation allowing virtually unlimited X-ray sessions without forced cool down delays.• The MRC tube runs silently offering a more comfortable patient environment.• Another secret of the MRC tube is the enormous heat storage capacity of its 200 mm diameter anode, eliminating waiting times.• And, the MRC X-ray tube can image the heaviest patients even at steep angles, while maintaining image quality. 79 X-Ray Tubes 79
2/24/2010 85 Patient support AngioDIAGNOST 5 Length: 303 cm (119.3 inch). Metal-free overhang: 125 cm (49.2 inch). Width: 50 cm (19.7 inch). Longitudinal float: 100 cm (39.4 inch). Transverse float: 36 cm (14.2 inch). Height adjustment (without pivot option): 76 to 104 cm (29.9 to 40.9 inch). Maximum levelling speed (height adjustment): - 2 cm/s (0.8 inch/s). Table tilt: L-arc position Angulation (degrees) Rotation (degrees) Head-end of table 45 Caudal to 45 cranial 27 RAO to 115 RAO 85 85
2/24/2010 86 Light intensity: 30,000 Lux. Colour temperature: 4300° K. Focusable light field size: 14 - 25 cm (5.5 - 9.8 inch). Working distance: 70 -140 cm (27.6 - 55.1 inch). Light intensity at 30,000 Lux: 114 W/m2. Lamp type: halogen 22.8 / 24 V 50 W. Mains power: 220/240 V. 86 Examination light 86
2/24/2010 87 Quality Assurance Weekly 3D calibration is carried out. The calibration data is valid for only 14 days (7 days pre- and post- acquisition). The calibration is to rectify S-distortion as well as pin cushion distortion. S-distortion is caused by geo- magnetic field s on moving electrons within the Image Intensifier and pin cushion distortion is caused by the curvature of the input phosphor of the Image Intensifier.
2/24/2010 88 DoseWise is active throughout at every level of system - from spectra beam, pulsed fluoroscopy to syncratouch. It ensures every possible opportunity to reduce dose, while maintaining image quality. DoseWise includes three highly effective strategies for dose management: Spectra Beam technology to remove unwanted ‘soft’ radiation and minimize scatter radiation, automatically. Spectra Beam filters during fluoro and exposures remove unwanted soft radiation, i.e. those X-rays that hit the patient but do not have enough energy to reach the image detector. In this way, filtering significantly reduces patient dose and scattered radiation for staff while maintaining a high image quality.
2/24/2010 90 DIS-ADVANTAGES OF DSA Mis-registration . Poor resolution compared to conventional angiography. User dependent success rate. Risk of emboli may reaching to healthy tissue. Not suitable for everyone.
Despite recent advances in CT angiography and MR angiography, digital subtraction angiography (DSA) remains the standard imaging technique for evaluation of the cerebral vasculature .
Three-dimensional (3D) reconstruction of the dataset acquired during rotational DSA represents the latest development in the neurovascular imaging armamentarium.
This technique combines the anatomic resolution of DSA with the 3D visualization abilities previously offered by only CT or MR angiography and provides more detailed information than does DSA alone in the evaluation of neurovascular lesions, such as cerebral aneurysms .
3D-DSA has taken a prominent role in treatment planning by enabling better appreciation of the morphology of complex vascular lesions before endovascular or surgical management.
It is also superior in the performance of sophisticated tasks such as aneurysm volume measurement
On the other hand, the inability of 3D-DSA to simultaneously image osseous and vascular structures is noted as a weakness of this technique compared with CT angiography .