The Role of Computers in Medical Physics

THE ROLE OF
COMPUTERS IN
MEDICAL PHYSICS
Victor EKPO
MSc Medical Physics prog., College of Medicine, University of Lagos, Lagos. 2017
1

WHAT IS IT ALL ABOUT?
2
DATA
The computer takes analogue data, converts them into digital
bits (0 & 1), using software programs to provide speed and
precision.
The computers role now includes Pervasive Computing and the
new bride of the computing world, the Internet of Things (IoT).
THE ROLE OF COMPUTERS IN MEDICAL PHYSICS. VICTOR EKPO. CMUL - LAGOS

INTRODUCTION
Computers help with:
• Speed
• Automation
• Accuracy
3

In Medical Physics, focus has recently been on:
• digitization of images,
• computerization of radiography,
• treatment automation
4

ROLES OF COMPUTER IN MEDICAL PHYSICS
 Database Management
 Radiodiagnosis
 Image Display
 Image Processing
 Digital Radiography
 Computer – Aided Diagnosis
 Imaging Modalities (e.g. CT, MRI, SPECT, PET)
Radiotherapy
 Computerised Treatment Planning
 Radiotherapy techniques
Dosimetry
5THE ROLE OF COMPUTERS IN MEDICAL PHYSICS. VICTOR EKPO. CMUL - LAGOS

DATABASE MANAGEMENT
The advantages of the computer include its ability to:
• Store large volumes of data.
• Retrieve data within the shortest possible time, with precision.
• Secure (confidential) data, using authentication and
authorization.
• Share data faster and easily, to people of interest.

Data may be:
• patient’s information (e.g. clinical history, radiographs),
• machine (e.g. calibration measurements, service history),
• staff records (payroll, research work), etc.

PACS
• Many radiographic centres now adopt a network called
Picture Archival and Communication System (PACS) .
• PACS connects different units, departments and hospitals
to a single computer network.
DATABASE MANAGEMENT

The PACS connects to the Radiology Information System (RIS), which is in turn
interfaced to a Hospital Information System (HIS).
Fig 3: Basic elements of
generic Picture Archival and
Communication System
(PACS)
(Image Source: Heggie JCP Applied
Imaging Technology)

• For modalities not using digital receptors but cassette films (e.g.
traditional x-ray), film images can be digitized using laser or charge-
coupled device (CCD) digitizers.
• A film digitizer is a device that scans the film with a light source,
measures the transmitted light, and forms a digital image depicting the
distribution of optical density (OD) in the film.
10

INFORMATION SHARING (contd.)
• This data can be transferred to workstations, remote
consoles, archival storage media and other computers within
or outside the Centre (teleradiology).
• Teleradiology helps provide radiological services to
smaller medical centres, as well as improve access
to specialty radiologists.

IMAGE DISPLAY
• The computer monitor serves as image display for radiographic
modalities, e.g. Ultrasound, Fluoroscopy.
• The computer (using colour monitors) is also able to enhance
interpretation of images by adding colour effects.

IMAGE DISPLAY (contd.)
VIDEO
Digital images can also be
converted into a video, by
aligning a set of succeeding
images in real time.
Fig 2: Real time ultrasound imaging.
Can now be shown in colour.
(Image Source: Pinterest.com)

IMAGE PROCESSING
• Image Co-Registration: Here, an image from one radiographic
modality (e.g. Computed Tomography [CT]) is superimposed
on an image from another modality (e.g. Positron Emission
Tomography [PET]) to form a better image outcome.
14

Fig: Image Co-Registration, using PET/CT
15
I II

IMAGE PROCESSING (contd.)
• Digital Subtraction: Whereas image co-registration adds
images from 2 different modalities to achieve one final
image, in Digital Subtraction, the computer subtracts
unwanted details from an image to achieve clarity.
• This is used in angiography (imaging of blood vessels).

• Spatial Filtering: A computer can also be used to reduce the
grainy appearance of the image (called quantum mottle) and
enhance quality of the image at the edges.

• Contrast Enhancement: The computer automatically maps
the data in such a way that optimizes the display of the
image, especially in enhancing areas of clinical
significance.
18

•3-D Reconstruction:
The computer achieves this using measurements of :
 Tissue linear attenuation coefficient
(for X-ray CT),
 Radionuclide concentration
(for SPECT/PET),
 Surface and volume rendering
(in Tomography).

DIGITAL RADIOGRAPHY
• Digital Radiography is fast replacing Film Screen
Radiography (use of screen-film cassettes).
There are 2 types of Digital Radiography Systems
• Computer Radiography (CR)
• Direct Digital Radiography (DR)

DIGITAL RADIOGRAPHY (contd.)
• CR uses Photostimulable Phosphor Plate enclosed in a cassette.
Image acquisition works in 2 separate steps:
Capture  then Read
21

• In DR, uses a new set of detectors that can capture and
read out simultaneously. It does not use cassette. DR
thus saves time and improves workflow, as it does not
require the loading of cassette, processing of film, and
cassette reloading.
22

DIGITAL RADIOGRAPHY (contd.)
• Digital Radiography provides better Contrast Resolution than
conventional Radiography, because of using techniques such as
slicing and windowing. Therefore, low contrast images are
better seen.
• However, it has poorer Spatial Resolution because of the limited
number of pixels used to view on a monitor at a time.
23

COMPUTER-AIDED DIAGNOSIS
• Using a software program, the computer is able to detect
areas of architectural distortions, microcalcifications and
abnormal masses, e.g. in early detection of lung and
breast cancer.
• This improves the sensitivity and specificity of the
radiographic image.
24

COMPUTERISED TREATMENT PLANNING
This involves the use of computers to determine the:
• Shape of Radiation Beam
Using configuration of Multi-Leaf Collimator settings on the
computer, radiation can be focused in such a way to maximum
dose to the tumour itself, and minimal dose to healthy tissues,
such as in 3D-CRT, IMRT.
RADIOTHERAPY

COMPUTERISED TREATMENT PLANNING (contd.)
• Dose Optimization and Distribution
The software calculates expected dose, and takes into
cognisance the SSD, TAR, Patient’s Surface/ Density/
Geometry, beam shape, intensity, and tissue
inhomogeneity.

• Inverse Treatment Planning
Used in Intensity Modulated Radiotherapy (IMRT).
The computer automatically develops the treatment
planning, given the Planned Target Volume (PTV), dose
required, and radiograph.
27

RADIOSURGERY (CYBERKNIFE & GAMMA KNIFE)
• The Gamma Knife incorporates 201 collimated cobalt-60 sources for
head and neck cancer treatments, while the CyberKnife incorporates a
miniature LINAC mounted on a robotic arm. Each aided by computer
algorithms to deliver precise high dose rates to target volumes.
CyberKnife Gamma Knife

COMPUTERS IN ULTRASOUND
• Digital systems are used in Ultrasound as display monitors
(e.g. digital scan converters), in image acquisition, image
processing and storage.
29

• Modern phased array transducer design for multi-
frequency transducer operation, allows computerized
beamforming where the centre frequency can be
adjusted in the transmit mode.
31

COMPUTERIZED BEAMFORMING
The Ultrasound beam can be focused at multiple transmit zones by using several pulses, for
different depths, transmitted at several times, steered to different angles.
32
Fig: Computer-controlled phased array beamforming

33
PHASED ARRAY BEAM SPHERICAL BEAM
Beam formed may be phased array or spherical beam (as used in
Ultrasound Computed Tomography).

COMPUTERS IN ULTRASOUND (contd.)
• Flow information and beamforming for array transducers can
be computationally designed.
• The imaging systems acquire and analyse the ultrasonic data,
and display the resulting images at real-time image rates (i.e.
faster than 30 frames per sec).
34

• Autocorrelation techniques are commonly used to
estimate flow velocities for colour flow imaging. To
minimize colour image noise, colour flow imaging
uses at least three pulses to estimate the flow
velocity for each pixel.
35

• 2D shows in greyscale.
• 3D provides colour and depth (3-D).
• 4D provides fast real-time ultrasound, which shows motion.
• HD provides very high resolution that makes it possible to
see physical facial features of the foetus.
36
21

ULTRASOUND CT (USCT)
• Using DSP, Ultrasound Computer
Tomography (USCT) produces 3D
images by lining several
ultrasound transducer arrays.
• Images can be constructed using
several algorithms, like the
Synthetic Aperture Focusing
Technique (SAFT).
37
Fig: Animation representing measurement procedure of
Ultrasound Computer Tomography System using
thousands of transducers

ULTRASOUND CT (USCT)
In breast diagnosis, the transducer aperture is usually a 18 x 26 cm semi-ellipsoidal
water-filled cavity at a resonance frequency of 2.5MHz.
(Image: Karlsruhe Institute of Technology (KIT), Germany)
38

USCT (contd.)
• Water is used as a low-attenuating transmission medium
between ultrasound transducers and object.
• Unlike conventional ultrasonography, which uses phased
array technology for beamforming, most USCT systems
utilize unfocused spherical waves for imaging.
39

ADVANTAGES OF USCT
• As transducers are not manually operated, the image
quality of USCT does not depend on the sonographer’s
performance or experience.
• USCT offers potentially increased specificity as
multiple breast cancer characteristic properties are
imaged at the same time.
40

• Using Digital Scan Converters, computers convert analogue
data (electrical signals from the transducer) to digital form
(numbers) and process them to display in pixels on a CRT
monitor.
• With computers, it is easier to achieve better axial and
lateral/spatial resolution.
41

42

IMAGING MODALITIES USING COMPUTER
ALGORITHMS
Most modern imaging modalities now use computer
algorithms in formulating radiographic images. This includes:
• Computed Tomography (CT),
• Magnetic Resonance Imaging (MRI)
• Single Photon Emission CT (SPECT),
• Positron Emission Tomography (PET).
43

COMPUTERS IN IMAGING MODALITIES(contd.)
• Computed Tomography [sometimes called Computed Axial
Tomography (CAT)] is a special x-ray equipment which uses an
array of digital detectors which scan through the patient from
different angles, producing transverse slices of tissues.
44

COMPUTERS IN IMAGING MODALITIES(contd.)
• It uses detectors with scintillators (emits visible light when
exposed to x-ray) and photodiodes (converts the visible light
into electrical signals). These electrical signals are then
computed and interpreted by computer algorithms to create
radiographs.
45

• CT provides far better images (better low contrast
resolution) than conventional X-ray, are better equipped
to avoid artefacts, can offer 3D imaging, and take
considerable shorter processing time.
46

DOSIMETRY
• Computers are used in a new Portal Dosimetry technique,
called Electronic Portal Imaging Device (EPID) – attached
to radio-machines, and transfers detector information to a
computer, where software is used to process information,
and monitor dose to patient.

• In the LINAC (for example), Computing Radiation Dosimetry
uses two ionization chambers (primary and secondary) to do
real-time measurement of dose, and terminates the beam when
the required dose is reached.
DOSIMETRY (contd.)

• If the primary dosimeter fails, the secondary dosimeter
automatically shuts down the radiation.
• This serves as an important radiation protection
measure to avoid accidents and overdose.
49

Video: Computerized Dosimetry & Radiation Protection using two Ion Chambers in LINACs (Video
Source: ELEKTA) 50

CONCLUSION
• Computers are a central part of medical imaging now and
the future.
• Thus, improvements with computer technology is most
likely to correspond to an improvement in the efficiency of
modalities and techniques of medical imaging.

REFERENCES
J. T. Bushbery, et al. The Essential Physics of Medical Imaging. 2nd ed. New York: Lippincott Williams &
Wilkins. 2002.
HD Ultrasounds: 4D Imaging (www.time.com/3805926/hd-ultrasounds-4d-imaging-of-your-unborn-child-is-
the-future/)
T. J. Hall, et al. Computers in Ultrasonic Imaging. Journal of Digital Imaging. Vol. 5 No. 1. 1992.
Hendee, W. R. Ritenour, E. R. Medical Imaging Physics. New York: Wiley-Liss. 2002.
Podgorsak, E. B. Radiation Oncology Physics: A Handbook for Teachers and Students. IAEA: 2005.
Huda, W. Review of Radiologic Physics. 3rd ed. Philadelphia: Lippincott Williams & Wilkins. 2009.
N.V. Ruiter, M. Zapf, et al. 3D Ultrasound Computer Tomography of the Breast (3D-USCT): A New Era.
European Journal of Radiology.
Heggie JCP, Liddell NA & Maher KP, Applied Imaging Technology, 4th Edition. 2001
52

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The Role of Computers in Medical Physics

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