1. Republic Of Yemen
Ministry Of Higher Education And Scientific
Research Modern Specialized University
Faculty Of Engineering And Smart Computing
Department Of Biomedical Engineering
2025-2024 , 1446: يساردال
ماعال
يبطال
التصيور
ةمظنأ
:
2
يبطه
هزهجا
Biomedical Equipment II:
Medical
Imaging System
ةعبارال
:
ةرضاحم
ال
Computed
Tomography (CT) Scan
ةينميال
ةيروهمجال
يملعال
ثحبالو
يالعال
ال
ت
عل
ي
م
ةرازو
ةثيدحال
ال
تخ
يصص
ة
ةعماجال
ةيكذال
ةبسوحالو
ةسدنهال
لكية
ةيويحال
ةيبطال
ةسدنهال
ق
س
م
لوأال
لصفال:
,
عبارال
ىوتسمال:
Medical Imaging Systems 1
Biomedical Equipment II Dr. Amine Aissa Mokbel Ali
2. CT : Introduction
CT produces cross-sectional images of the object of interest
through acquisition of multiple views, typically with X-ray
radiation.
Tomography is actually originated from the Greek words which are
‘tomos’ means slice, and the Greek word ‘graphein’ means write.
CT is a way of using X-rays to take detailed pictures or
images in very fine slices through the part of the body
that the doctor has asked to be investigated.
Many pictures (2D) of the same area are taken from many
angles and then placed together to produce a 3D image.
2D images of CT Scan of heart
Medical Imaging Systems 2
Biomedical Equipment II Dr. Amine Aissa Mokbel Ali
3D images for CT Scan of heart
3. CT : purpose
CT scanning is most often the method of preference for
detecting many different cancers since the doctor can
confirm the presence of a tumor and determine its size and
location from the images.
CT images of internal organs, bones, soft tissue and blood
vessels typically provide greater detail than traditional x‐
rays, particularly of soft tissues and blood vessels.
In emergency cases, the internal injuries and bleeding can be
quickly determined to help save lives, as the CT is fast,
painless, noninvasive, and accurate. CT scans are frequently
used to evaluate the brain, neck, spine, chest, abdomen,
pelvis, and sinuses.
CT has in fact revolutionized medicine because it allows
doctors to see diseases that, in the past, could often only be
found by autopsy.
Medical Imaging Systems 3
Biomedical Equipment II Dr. Amine Aissa Mokbel Ali
4. CT : purpose
CT has overcome the limitations of the conventional
medical radiography by completely eliminating the
superimposition of images of structures outside the
area of interest.
In addition, CT produces images with a high contrast
resolution, which makes it convenient to
differentiate between soft tissues that differ in
physical density even by less than 1%.
Computed tomography of the head
Medical Imaging Systems 4
Biomedical Equipment II Dr. Amine Aissa Mokbel Ali
5. CT : Principals
Block diagram of a CT system.
CT differs from conventional X ray
‐ techniques in that the images
displayed are not photographs but are reconstructed from a large
number of absorption profiles taken at regular angular intervals
around a slice of the body.
CT Scanner produces more detailed image rather than X-ray machine as CT
Scanner emits a series of narrow beam compare to diagnostic X-ray machine
only emit one way radiation beam.
In CT Scan the X-rays will be received by a detector that
is located on the opposite side of the Xray tube which
can see hundreds of different levels of density and also
tissues inside the organs.
Medical Imaging Systems 5
Biomedical Equipment II Dr. Amine Aissa Mokbel Ali
Then, images of the scan will be produced by
a computer and can be viewed on a
computer monitor, printed on film or
transferred to a CD or DVD.
Sometimes a contrast dye is used because it shows up much
more clearly on the screen. If a 3D image of the abdomen is
required the patient may have to drink a barium meal. The
barium appears white on the scan as it travels through the
digestive system.
6. CT : Construction
CT consists of an X ray
‐ subsystem, a gantry, a patient table, and a
controlling computer.
A high voltage X ray
‐ generator supplies electric power to the X ray
‐
tube, which usually has a rotating anode and is capable of
withstanding the high heat loads generated during rapid multiple slice
‐
acquisition.
The gantry houses the X ray
‐ tube, X ray
‐ generator, detector system,
collimators, and rotational frame.
The X ray
‐ tube and detectors are mounted opposite each other in the
rigid gantry with the patient lying in between and by moving one or
both of these around and across the relevant sections, which is how
the measurements are made.
The patient lies on a motorized couch and is moved into the aperture of the gantry, with the location to be
accurately determined by means of a narrow strip of light that falls on the body from the gantry and illuminates
the section to be examined.
Medical Imaging Systems 6
Biomedical Equipment II Dr. Amine Aissa Mokbel Ali
7. CT : Construction
All computed tomography systems consist of the following
four major subsystems :
(i) Scanning system: Takes suitable readings for a picture to
be reconstructed and includes X ray
‐ source and
detectors.
(ii)Data acquisition system (DAS):
Converts these readings into digital signals
readable with informatic system.
(iii)Image Reconstruction: creates images
using sophisticated computer algorithms.
(iv)Display, storage and Communication : Presents this information in visual
form and includes other manipulative aids to assist in diagnosis. And Enable the
information to be stored for subsequent analysis. Finally, the images can be sent
to remote locations.
Medical Imaging Systems 7
Biomedical Equipment II Dr. Amine Aissa Mokbel Ali
8. CT : Construction :Scanning system (X‐ray Source)
Medical Imaging Systems 8
Biomedical Equipment II Dr. Amine Aissa Mokbel Ali
The X ray
‐ tubes used in the CT scanners is the rotating anode air cooled type.
‐
It have a higher power capability for exposure times in the 2–20
second range.
The power requirements of these tubes are generally variable
within 100–160 kV.
Typical power requirements of these tubes are 120 kV at 200–500 mA,
producing X-rays with an energy spectrum ranging from approximately
30–120 keV.
Most systems have two possible focal spot sizes, approximately
0.5 mm × 1.5 mm and 1.0 mm × 2.5 mm.
A collimator assembly is used to control the width of the fan beam
between 1.0 and 10 mm, which, in turn, controls the width of the
imaged slice.
All modern systems use high frequency X ray
‐ generators,
typically operating between 10 and 50 kHz.
9. CT : Construction : Scanning system (Detector)
Medical Imaging Systems 9
Biomedical Equipment II Dr. Amine Aissa Mokbel Ali
The detector is one of the most important
components in the CT imaging chain because it
captures radiation passing through the patient and
converts it into electrical signals that subsequently
are digitized and sent to the computer for processing
and image building.
Currently, two categories of detectors capture and
convert radiation into digital data. These include
scintillation detectors (energy integrating detectors
and dual-energy detectors) and photon-counting
detectors.
10. CT : Construction : Scanning system (Detector)
Scintillation Detectors
The Energy Integrating Detector (EID) is based on the
use of scintillation crystals that convert X-ray photons to
light photons, which are then converted to electrical
signals by photodiodes.
Detector electronics called application-specific
integrated circuits (ASIC) digitize the signals.
Dual-energy CT
By making use of principle of comparing the
attenuation of different materials when exposed to
high and low energy levels, dual-energy CT can help
to improve material differentiation.
Various dual-energy computed tomography systems (DECT) are currently available on the market. (a) Dual source DECT: two source X-ray
tubes are placed orthogonally to each other with corresponding detectors. (b) Rapid voltage switching DECT: single source which is
capable of rapid voltage switching between low and high energies with a corresponding single detector. (c) Dual layer DECT: Single source
and single detector, which consists of two different layers of detectors to separate low- and high-energy spectra.
Medical Imaging Systems 10
Biomedical Equipment II Dr. Amine Aissa Mokbel Ali
11. CT : Construction : Scanning system (Detector)
The photon-counting detector
These detectors use semiconductors such as cadmium
telluride (CdTe) and cadmium zinc telluride (CZT)
because they can convert x-ray photons directly into
electron hole pairs (electric charge).
It has the ability to detect each photon (and its
estimate energy) individually with the help of fast
read-out circuits. An individual photon is detected
by checking if the induced charge is above a
certain level.
Medical Imaging Systems 11
Biomedical Equipment II Dr. Amine Aissa Mokbel Ali
12. CT : Construction : DAS
Data Acquisition System
A typical CT data acquisition system (DAS) consists of
precision pre amplifiers,
‐ current to voltage
‐ ‐ converters,
analog integrators, multiplexers, and analog to digital
‐ ‐
converters (ADCs), and computer system.
Modern systems make use of optical or
wireless transmitters on the rotating gantry
to send data to fixed optical receivers.
Photodetector arrays used in CT imaging
have as many as 1000 detectors in the
semicircular detector arch.
After amplification, ADCs convert the
analog signals to their corresponding
digital signals. The sampling speed of the Medical Imaging Systems 12
Biomedical Equipment II Dr. Amine Aissa Mokbel Ali
13. CT : Construction : DAS
Data Acquisition System (suit)
The ADCs must have high dynamic range with at
least 32 bit resolution or greater that are
commonly used.
The outputs of the ADCs (digital data ) then go
to an image signal processor over a high speed
link for further signal processing and image
reconstruction.
Control cards include digital signal processors
(DSPs) and field programmable gate arrays (FPGAs), power supplies, clocks and
clock distribution circuitry, and interface blocks.
The image reconstruction card is connected to the host computer where the CT
images are reconstructed by combining the digital data by the selected
mathematical procedure of tomographic reconstruction.
Medical Imaging Systems 13
Biomedical Equipment II Dr. Amine Aissa Mokbel Ali
14. CT : Construction :Image Reconstruction
Image Reconstruction
Image reconstruction uses algorithms, or
defined rules for solving a problem, to
systematically build an image during the
scanning process.
The algorithms used in CT include the
earlier back projection algorithm and
newer analytic reconstruction techniques
such as the filtered back projection
algorithm.
Medical Imaging Systems 14
Biomedical Equipment II Dr. Amine Aissa Mokbel Ali
15. CT : Construction :Display, storage and Communication
The fourth main component of CT systems involves
displaying the reconstructed image for viewing and
interpretation, with postprocessing to suit the needs
of the interpreting radiologist.
Additionally, images are sent to PACS (Picture
Archiving and Communications System ) for storage
and communication to virtual data centers for
retrospective analysis.
For effective electronic communication in CT, a
standard protocol is required to facilitate connectivity
(networking) among imaging modalities and
equipment from various manufacturers. The standard
employed for this purpose is Digital Imaging and
Communication (DICOM).
Medical Imaging Systems 15
Biomedical Equipment II Dr. Amine Aissa Mokbel Ali
16. CT : Evolution (Generation)
There are several designs of scanning arrangements that have been
commercially developed. They have many generation and used different
mechanical configurations for mounting X ray
‐ source and detectors.
First generation
‐ scanners:
based on the ‘traverse and index’
used a narrow pencil beam and a detector on the other side of the patient.
The detector moves on a gantry along with the X ray
‐ tube.
The tube and detector move in a straight line and sample the data 180 times.
After reaching the end position of the scan, the scanner gantry moves to the
next position with a 1° tilt for the next translation across the patient.
Second generation
‐ scanners:
a fan beam of X rays
‐ and a bank of
detectors. takes several profiles with each
traverse and thus permits greater index
angles.
scan times could be considerably reduced to
about 10–30 seconds range.
Medical Imaging Systems 16
Biomedical Equipment II Dr. Amine Aissa Mokbel Ali
17. Third generation
‐ scanners:
wide fan shaped
‐ X ray
‐ beam.
multiple detector.
the rotational movement is not stepwise but continuous.
wide fan beam, typically between 30° and 50° and rotates
usually through 360°.
time may be reduced to only a few seconds.
Fourth generation
‐ scanners:
the detectors are placed in a 360° ring around the patient.
X ray
‐ source that rotates around the patient.
employs as many as 2000 detectors .
a few seconds or even less.
CT : Evolution (generation)
Medical Imaging Systems 17
Biomedical Equipment II Dr. Amine Aissa Mokbel Ali
18. Spiral/Helical Scanning
the patient couch is moved through the bore of the
scanner, while the gantry rotates.
is often referred to as helix, spiral, volume, or 3D
CT scanning.
In helical scanning, the patient table speed of 1–10
mm/s and complete 360° rotations are achieved in half
a second or less with the fan beam collimated to 1–10
mm thick slice.
CT : Evolution (generation)
Medical Imaging Systems 18
Biomedical Equipment II Dr. Amine Aissa Mokbel Ali
19. Mult-slice Computed Tomography
Typically offered simultaneous acquisition of data for four slices.
improvement towards the goal of 3D imaging and reconstructing
the images at any position along the patient axis.
the detector arrays are one dimensional and consist of a
large number (typically 750 or more) of detector
elements in a single row across the irradiated slice to
receive the X ray
‐ fan beam.
With the help of modern CT, it is possible to visualize anatomy as small
as 150 μm, providing CT image quality with resolution typically seen
only in cath labs. This has become possible with the use very thin
detectors having size of the order of 0.25 mm/ slice.
CT : Evolution (generation)
Medical Imaging Systems 19
Biomedical Equipment II Dr. Amine Aissa Mokbel Ali
