5133aa1d673894d5a05b9d83809b9dbe original

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:


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 xray 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 single-slice 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 2-dimensional 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



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

Two x-ray tube coupled to two separate detector system
Det A which covers the entire
diameters)

scan FOV(50 cm in


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
simultaneously

up

to

64

(128

-

256)

slices

can

be

collected

 3-D CT and CT endoscopy
 Cardiac

image acquisition
synchronization)

during

relevant

heart

phases

(ECG

pulsing

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.
2.
3.

Continuous scanning mode made possible by
principle

spiral/helical scanning

Fast image reconstruction made possible by special hardware performing
quick calculations and a new image reconstruction algorithm
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…!


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