This document provides an overview of various CT scanning technologies including spiral/helical CT, MSCT/MDCT, dual source CT, EBCT, CBCT, and portable CT. It discusses the history and development of these technologies, their operating principles, advantages and disadvantages, and clinical applications. The key points are: - Spiral/helical CT allowed continuous scanning of volumes using simultaneous patient translation and tube rotation. - MSCT/MDCT increased volume coverage speed using multi-detector arrays scanning multiple slices per rotation. - Dual source CT uses two x-ray tubes and detectors for improved temporal resolution. - EBCT was an early technique using a stationary electron beam that allowed very fast cardiac

1. SPIRAL/ HELICAL, MSCT/ MDCT, DUAL
SOURCE CT, EBCT, CBCT, PORTABLE CT
AASIF MAJEED LONE
ASSISTANT PROFESSOR
CENTURION UNIVERSITY

2. Content
■ Spiral/ helical
■ MSCT/MDCT
■ Dual source CT
■ EBCT
■ CBCT
■ Portable/Mobile CT

3. History
■ Dr. Kalender was born in 1949 and studied medical physics in Germany.
■ In 1989, the first report of a practical spiral CT scanner was presented at the
Radiological Society of North America (RSNA) meeting in Chicago by Dr. Willi
Kalender.
■ Dr. Kalender has made significant contributions to the technical development
and practical implementation of this approach to CT scanning. His main
research interests are in the areas of diagnostic imaging, particularly the
development and introduction of volumetric spiral CT.
■ He later worked with Siemens Medical Solutions in the area of CT, and in 1995
he became professor and chairman of the Institute of Medical Physics, which is
associated with the University of Erlanger, Germany.

4. ■ The spiral/helical CT scanners developed after 1989 were referred to as
single-slice spiral/helical or volume CT scanners. In 1992 a dual-slice spiral/
helical CT scanner (volume CT scanner) was introduced to scan two slices per
360-degree rotation, thus increasing the volume coverage speed compared
with single-slice volume CT scanners.
■ In 1998 a new generation of CT scanners was introduced at the RSNA meeting
in Chicago. These scanners are called multislice CT (MSCT) scanners because
they are based on the use of multidetector technology to scan four or more
slices per revolution of the x-ray tube and detectors, thus increasing the
volume coverage speed of single slice and dual-slice volume CT scanners.

5. Introduction
■ In conventional CT the patient is scanned one slice at a time. The x-ray tube
and detectors rotate for 360 degrees or less to scan one slice while the table
and patient remain stationary.
■ This slice-by-slice scanning is time consuming, and therefore efforts were
made to increase the scanning of larger volumes in less time.
■ A technique in which a volume of tissue is scanned by moving the patient
continuously through the gantry of the scanner while the x-ray tube and
detectors rotate continuously for several rotations

6. ■ Simultaneous patient translation and x-ray scanning generates volume of data.
■ X-ray beam traces a helix of raw data from which axial images must be
generated
■ Each rotation generates data specific to an angled plane of section
■ Transverse images can be reconstructed at any z-axis position
■ Movement of x-ray tube is not a spiral
■ Appears so because of translation movement of the patient

8. Technological
developments/Technological
consideration of helical/spiral CT
Three technological developments:
1. Slip-rings gantry designs
2. Very high power x-ray tubes
3. Interpolation algorithms to handle projection data

9. Type of spiral
CT
Single slice
spiral CT
Multi slice
spiral
CT(MSCT)

11. Single slice CT
■ Acquires one slice at a time. Table moves to start the acquisition of next slice
■ Long acquisition time

12. Dual slice CT scanner
■ The history of scanning more than one slice at a time (actually two-slice scanners)
dates back to one of the early EMI (London, United Kingdom)CT scanners, which
became available in 1972.
■ These scanners used two detectors and they are based on the translate/rotate
method of data collection over 180 degrees
■ The next major step to multi slice CT scanning appeared in 1993,with the
introduction of the first dual-slice volume CT scanner
■ the dual scanner slice geometry is based on a fan-beam of x-rays falling on two
rows of detectors instead of one row of detectors, characteristic of the single-
slice CT scanner beam geometry
■ The dual-slice whole-body fan-beam CT scanner offers improved volume coverage
speed performance compared with the single-slice volume CT scanner, reducing
the scan time by 50% while maintaining image quality for the same scanned
volume.

13. MSCT/MDCT
■ It is based on 3rd generation geometry

14. Advantage of MSCT
■ multi-slice CT (MSCT) are higher patient comfort-in the form of shorter and
fewer breath-holds in body imaging
■ Avoiding and minimizing sedation for pediatric patients
■ Critically ill patients can also be scanned much faster.

15. Advantage of MDCT
■ The latest breakthrough in CT technology
■ The primary diff between single slice CT (SSCT) & MDCT hardware is in the
design of the detectors arrays
■ Faster gantry rotation
■ Fast data acquisition system
■ High speed image reconstruction system
■ Multiple reconstruction technique

16. Dual Source CT
■ DSCT is equipped with two x-ray tubes producing different voltages (kVp)
offset at approximately 90°.
■ Two corresponding detectors are oriented into the gantry with an angular
offset of 90 degrees
■ excellent temporal resolution as both datasets acquired at the same time

18. Acquisition technique
■ There are different DECT acquisition technologies available from different
vendors.
■ These can broadly be classified as techniques that occur before the patient is
scanned (prospective) which need to be pre-selected and those that occur
after the patient is scanned (retrospective)

19. Prospective techniques
■ Dual-source
o Two x-ray tubes producing different voltages (kVp) offset at approximately 90°
o Reconstructed in the image space
o Limited field of view (FOV) as both detectors can' be the same size
o Excellent temporal resolution as both datasets acquired at the same time

20. Single-source consecutive
 Two helical scans are consecutively acquired at different tube potentials
followed by coregistration for postprocessing
 Reconstructed in the image space
 Full FOV
 Poor temporal resolution as the patient is scanned twice (therefore increased
dose)

21. Single-source twin-beam
 Two-material filter splits the x-ray beam into high-energy and low-energy
spectra on the z-axis before it reaches the patient

22. Single-source sequential ("rotate-rotate")
 Each x-ray tube rotation is performed at high- and low- tube potential
 Reconstructed in the image space
 Full FOV
 Poor temporal resolution as the patient is scanned twice (therefore increased
dose)

23. Single-source rapid kilovoltage switching
(fast kVp switch)
 The x-ray tube switches between high- and
low- tube potential multiple times within the
same rotation
 Reconstructed in the projection space
 Full FOV
 Slight reduction in temporal resolution due to
tube rotation

24. Retrospective techniques
■ Dual-layer DECT ("sandwich")
o The top (innermost) layer of the detector absorbs low-energy photons while
high-energy photons pass through to the bottom (outermost) layer
o Reconstructed in the projection space
o Full FOV
o Excellent temporal resolution as both datasets acquired at the same time

27. Advantages of DSCT
■ High temporal resolution
■ Faster acquisition
■ Artifact reduction

28. Applications of DECT
■ Tissue characterization
■ Liver lesion characterization
■ Renal mass characterization
■ Renal stone characterization
■ Oncologic imaging
■ Vascular imaging
■ Automated Bone Removal in CT Angiography
■ Urinary Stone Characterization

29. EBCT
■ 1st introduce by the group of researchers in Douglas Boyd at university of San
Fransisco
■ Introduced clinically in the 1980s, electron beam computed
tomography (EBCT) scanners are primarily used in adult cardiology to image
the beating heart.
■ The company Imatron Inc. started commercial production and distribution of
EBCT system in 1984
■ The sole manufacture of EBCT systems developed several scanner generation
■ EBCT/EBT/UFCT/CineCT

31. ■ As opposed to traditional CT scanners, EBCT systems do not use a rotating
assembly consisting of an x-ray source directly opposite an x-ray detector.
Instead, EBCT scanners use a large, stationary x-ray tube that partially
surrounds the imaging field
■ The x-ray source is moved by electromagnetically sweeping the electron beam
focal point along an array of tungsten anodes positioned around the patient.
■ The anodes that are hit emit x-rays that are collimated in a similar fashion to
standard CT scanners. Because this is not mechanically driven, the movement
can be very fast.
■ In fact, EBCT scanners can acquire images up to 10 times faster than helical
CT scanners. Current EBCT systems are capable of performing an image sweep
in 0.025 seconds compared with the 0.33 seconds for the fastest mechanically
swept CT systems.

32. ■ This rapid acquisition speed minimizes motion artifacts, enabling the use of
EBCT scanners for imaging the beating heart. In addition to faster image
acquisition times resulting in decreased motion artifacts, EBCT scanners
generally result in a 6- to 10-fold decrease in radiation exposure compared
with traditional CT scanners.
■ To date, EBCT scanners have not yet seen widespread adoption. The systems
are necessarily larger and more expensive than helical CT scanners. Advances
in multidetector helical CT scan designs have enabled cardiac imaging using
standard, mechanically driven systems.

33. ■ The use of EBCT in the pediatric population has primarily been reported for
the imaging of cardiac anomalies
■ we increasingly understand the risks associated with ionizing radiation
exposure in children, the decreased exposure associated with EBCT systems
appears attractive.
■ In addition, the faster acquisition times and minimization of motion artifact
could theoretically result in decreased sedation requirements in young
patients.
■ the potential advantages of decreased radiation exposure and sedation
requirements associated with EBCT systems.

36. EBCT is used to
■ Create a calcium score, based on calcium deposits in the coronary arteries
■ Make predictions about coronary heart disease (CHD)
■ Take a look at bypass grafts
■ Take a look at lesions, or sores, in your heart muscle
■ Evaluate the muscle mass in your heart
■ Check on heart function

37. Benefits of Electron Beam
Computed Tomography
■ It is less risky than more invasive tests for the presence of atherosclerosis.
■ It can show signs of heart disease before you have symptoms — but in time to
make changes that could prevent a heart attack.
■ An EBCT scan takes less than 20 minutes and you can return to normal
activities immediately afterward.

38. Risks of Electron Beam Computed
Tomography
■ As with other tests that involve radiation exposure, there is concern about the
dose of radiation you receive. While it's safe for most adults, you still may
want to talk to your doctor about safe radiation levels.
■ Although EBCT provides interesting information, there is no clear data showing
whether changes made because of EBCT results prevent heart attacks.
Whether you choose to have this test or not, you can make the changes in your
life that will help prevent heart disease and heart attack

39. Volume CT Scan
■ Flat-panel Volume CT is a technique under development to make computed
tomography images with improved performance (in particular, with improved
spatial resolution).
■ The key difference between volume CT and traditional CT is that volume CT
uses a two-dimensional x-ray detector orientation (usually in a square panel
orientation), to take multiple two-dimensional images.
■ On the other hand, the conventional CT uses a one-dimensional x-ray detector
orientation (a row of detectors) to take one-dimensional x-ray images.

40. ■ A CT machine consists of an x-ray source, an x-ray detector, a series of moving
stages (Gantry) and computers to assemble the x-ray data into an image.
■ The x-ray beam used in volume CT is cone shaped, in contrast to the fan
shaped beam of the regular CT scanner.
■ This cone shape allows the beam to cover the two-dimensional detector
panel.
■ USES OF VOLUME ACQUISITION CT SCAN is small tumors are not missed in
between the slices and easy diagnosis of even small tumors

42. CBCT:
■ CBCT is an emerging variant that uses divergent x rays forming a cone
between the source and detector unlike fan beam geometry in conventional
MDCT.
■ In CBCT multiple images are acquired during a single rotation of the gantry
around the patient head producing a three-dimensional volumetric data.
■ During a CBCT scan the scanner rotates around the patients head
approximately 30 sec obtaining nearly up to 600 images .These data are used
to reconstruct a 3D image of the following region of the patient’s
anatomy(teeth , jaw, neck, ear, nose etc).

43. Detectors:
■ Cone beam CT scanners use indirect flat panel detectors such as CsI
scintillation detector unlike ceramic detectors used in MDCT. These scanners
uses a high resolution two-dimensional detector instead of a series of row of
one-dimensional detector elements used in MDCT.
■ However detectors used in CBCT suffer from a greater lag(after glow) hence
acquisition time is much longer in CBCT relative to MDCT . Thus reducing
temporal resolution of CBCT scanners.

45. Reconstruction:
■ The volumetric data obtained in CBCT is similarly manipulated
and reconstructed into 3D images as in MDCT and can be viewed
in a variety of ways including MPR and volume rendering images.
■ The most commonly used reconstruction algorithm used in CBCT
is Feldkamp algorithm which is a modification of filtered back-
projection method.
■ CBCT takes longer time for reconstruction of images despite the
acquisition being done in single rotation.

47. Advantages of CBCT:
■ The major advantage of CBCT is reduction of radiation dose compared to
MDCT . For example effective dose that we encounter in commercial CBCT
scanner has been estimated as 0.2mSv Vs 1-2 mSv in MDCT head.
■ Compact design ,smaller in size thus cheaper than MDCT.
■ Decreased metal artifacts make CBCT scanners ideal for dental imaging as
well as in otorhinolaryngology where visualisation of small bones is of
paramount importance.

48. Disadvantages of CBCT:
■ Long acquisition time.
■ CBCT suffers from poor contrast resolution due to high scatter in cone beam
acquisition.
■ Limited anatomic coverage (small FOV) as it is based on acquisition of images
during single gantry rotation.
■ Lower QDE thus reducing the dynamic range of scanners.

49. Applications of CBCT:
■ CBCT found widespread applications in maxillofacial imaging including dental
imaging , sinus and temporal bone imaging.
■ Various clinical applications include visualisation of abnormal teeth,
evaluation of the jaws and face, cleft palate assessment endodontic diagnosis
etc.

50. C-arm CBCT:
■ Also called portable CBCT has been developed to improve patient comfort as it
eliminates the need for transporting the patient to the CT room for procedures
requiring guidance of cross-sectional imaging.
■ Portable CBCT scanner mainly finds its application in intraoperative as well as
interventional procedures like surgical planning in orthopaedic , chest,
abdominal and neurosurgical procedures.

51. 4-D Computed tomography
■ 4-D CT is one of the most important topics in medical imaging field that
attract tremendous interests nowadays . It is basically an advance dynamic
volume imaging which captures multiple images over time . 4-D CT has been
mainly developed to track physiological processes like respiration and internal
movement as well.

53. ■ IN 4-D CT the images are taken at different respiratory phases and then
reconstructed individually by using standard FBP method to produce 4D CT image
which is similar to traditional CT showing :
■ Body’s breathing.
■ Tumour movement etc.
■ However 4-D CT reconstruction requires large number of projections to achieve
decent image quality./
■ The principle advantage of 4-D CT is reduction of motion artifacts caused by
breathing thus helps in better tumour delineation . So by suppressing internal
movement moving tumours especially in lung and abdominal imaging can be
evaluated appropriately.

55. Portable CT:
■ A mobile CT has been developed in which gantry translation occurs rather than
translation of the patient table . So this permits in situ patient who is
positioned on radiolucent surface that fits within the aperture of gantry. Thus
provides head examinations directly at patient’s bedside.
■ World’s first portable CT scanner that has been developed is 32 slice BodyTom
scanner . This system incorporates an impressive 85 cm gantry and 60 cm FOV
, the largest FOV available in a mobile CT.
■ FEATURES:
■ Integrated front camera for safe maneuvering
■ Unique telescopic gantry for convenient patient positioning.

56. ■ Battery powered system compatible with PACS system.
■ Self-shielded gantry .
The initiative of Portable CT was first taken by Brihan Mumbai Municipal
corporation(BMC) and later followed by King Edward Memorial(KEM) hospital in
Mumbai.
This machine is only used in high profile institutions like Medanta hospital located
in Gurugram as well as in AIIMS Delhi.

58. Advantages and Disadvantages:
■ Allows imaging to be performed in operating room, thereby reducing the need
to transport the patient to radiology department.
■ Allows advanced intra-operative imaging of the brain and spine for image-
guided surgery.
■ Time saving and cost efficient.
■ Disadvantages:
■ High radiation dose.
■ Poor x ray output.

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