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CT physics and instrumentation
Lecture (7)
Multi-Slice Computed Tomography (MSCT)
And
Clinical application
RSSI 471
Prepared by
Mr. Essam Mohammed Alkhybari
Staff contact information:
• Mr. Essam Mohammed Alkhybari
• Radiological science and Medical Imaging Department
• Lecturer in Nuclear Medicine stream
• E-mail: [email protected]
Objective:
1.
2.
3.
4.
Background
MSCT principle
Dual source CT scan
Clinical application of
MSCT scan
Background: the evolution of MSCT scanners,
including the DSCT scanner
 1989: Single slice spiral/Helical CT scanner= 1 slice per revolution
 1992:Dual slice CT scanners= 2 slice per revolution
 1997: Four slice CT scanners= 4 slices per revolution
 2000: 8-16 and 32-40 slice CT scanner=8,16,32, and 40 per
revolution
 2004: 64 slice scanners= 64 slice per revolution
 2006: Dual source CT scanner= 2 x-ray Tubes coupled 2 detectors
arrays
 2006/2007: 320 and 256 slice CT scanners 320 & 256 slice per
revolution
 Future: ?
Background:
 Slip ring scanners and helical (spiral) CT were rapidly
adopted and became the standard of care for body CT
 However, a significant problem became evident: helical CT
was very hard on x-ray tubes.
 As a result, the more rotation of x-ray tube, creates huge
amounts of heat which effects the ability of the scanner.
Background:
 A straightforward solution to this heat issue, of course, is to
develop x-ray tubes with a higher heat capacity
 Another approach is to more effectively use the available x-ray
beam: if the x-ray beam is widened in the z-direction (slice
thickness) and if multiple rows of detectors are used, then data
can be collected for more than one slice at a time
 This approach would reduce the total number of rotation and
therefore the total usage of the x-ray tube needed to cover the
desired anatomy. This is the basic idea of MSCT.
MSCT Detectors:
 The primary difference between singleslice CT (SSCT) and MSCT hardware is in
the design of the detector arrays
 In MSCT, each of the individual,
monolithic SSCT detector elements in the
z-direction is divided into several smaller
detector
elements,
forming
a
2dimensional array Rather than a single
row of detectors encompassing the fan
beam, there are now multiple, parallel
rows of detectors
Multi-Slice Spiral/Helical CT:
 This types of scanner referred to as
volume CT (VCT) Systems because
covering entire body sections is easily
accomplished in a sing breath holds
 The advantage of MSHCT include
isotropic viewing, longer anatomic
coverage, multiphase studies , faster
examination times, and improved
spatial resolution
 The advancement of VCT, with
increasing larger detectors arrays,
promises to provide unique clinical
opportunities in diagnostic medicine
MSCT CONCEPTS: differences between
MSCT AND SSCT
Slice Thickness: Single Detector Array
Scanners:
 The slice thickness in single detector
array CT systems is determined by the
physical collimation of the incident x-ray
beam with two lead jaws.
Slice Thickness: Multiple detector
Detector Array Scanners:
 The slice thickness of multiple detector
array CT scanners is determined not by
the collimation, but rather by the width
of the detectors in the slice thickness
dimension
Cone beam and Fan beam geometry:
 A cone beam geometry produce more
beam divergence along the z-axis
direction compared with fan beam
geometry
 For this reason increasing the number of
detectors rows in MSCT crates a need for
a different approach to the interpolation
process because the rays that contribute
to the imaging process are more oblique
 Additionally, the number of detectors
rows plays an important role in slice
thickness selection and volume coverage
Dual-source CT scanner
 This dual source CT scanner (DSCT)
that features two x-ray tubes and two
detectors specifically intended for
imaging cardiac patients in a very
short time
Dual-source CT scanner:
Major Technical components:
 Tow data acquisition system (DAS) offset by 90
degree
 Two x-ray tube coupled to two separate
detector system
 Det A which covers the entire scan FOV(50 cm
in diameters)
 Det B which covers smaller central scan FOV (26
cm in diameter)
 Each x-ray tube is STARTON type that uses the
z-flying focal spot technique and cone beam
geometry to image 32-slices combined to
produce 64 slices per revolution
 Each x-ray tube can be operated separately, so
the scanner can perform dual energy imaging,
where one tube operate at 80 kVp and other at
140 kVp
Single source CT
Fast + Poor Image quality
Dual Source CT
Fast + Improved Image quality
Clinical application of MSCT scan:
The new helical scanning CT units allow a range of new features, such as :
 CT angiography
 CT fluoroscopy, where the patient is stationary, but the tube continues
to rotate
 multislice CT, where up to 64 (128 - 256) slices can be collected
simultaneously
 3-D CT and CT endoscopy
 Cardiac image acquisition during relevant heart phases (ECG pulsing
synchronization)
CT angiography (CTA):
• CT angiography defines as CT
imaging of blood vessels
opacified by contrast media
• Images can be captured when
vessels are fully opacified to
demonstrate either arterial or
venous phase enhancement
through the acquisition of
both data sets ( arterial and
venous).
CTA
CT Fluoroscopy:
• Real Time Guidance
(up to 8 fps)
• Great Image Quality
• Low Risk
• Faster Procedures
• Approx. 80 kVp, 30 mA
CT Fluoroscopy:
CT fluoroscopy is based on three advances in CT technology:
1.
Continuous scanning mode made possible by spiral/helical
scanning principle
2. Fast image reconstruction made possible by special hardware
performing quick
calculations and a new image
reconstruction algorithm
3. Continuous image display by use of cine mode at frame rates
of two to eight images per second.
CT Endoscopy-Virtual Reality(VR) Imaging:
 VR is a branch of computer science that
immerses users in a computer-generated
environment and allows them to interact 3D
scenes.
 A virtual endoscope is a graphic based
software system used for simulating
endoscopic exploration inside a 3Dimage.
 In virtual endoscopy, a 3D image acts as
‘copy’ or virtual environment, representing
the scanned anatomy
Types of Coronary CT imaging:
 MSCT (multislice CT) : A new form of cardiac
imaging. This is a way to measure obstruction similar
to a cardiac catheterization. It is NOT a functional
test.
 Coronary Calcium Scoring: calcium scoring for risk
assessment. This is for asymptomatic patients and is
not yet recommended as a routine screen. (CCS can
be normal in 5% of patients who have myocardial
infarcts)
MSCT Coronary Angiography:
Details
 Initial studies 5-10 years ago used 4-slice MSCT.
Then came 16-slice (we still use these in some
centers) and now 64-slice MSCT is arriving in just
the last few years.
 The 64-slice CT is the current standard (approved in
2004), can handle faster heart rates
 256-slice CT angiograms are just starting to be
evaluated.
64-Slice CT Scanner
 More coverage (volume) with each heart beat
 Entire heart imaged in 5-15 seconds
 Less contrast required
 No increase in rotation speed, but with overlapping
slices, can use segments from different heart beats to
improve temporal resolution
3-D Volume Rendered Image
Questions…!