AASCIT Journal of Health

2018; 5(1): 21-27

http://www.aascit.org/journal/health

ISSN: 2381-1277 (Print); ISSN: 2381-1285 (Online)

Keywords

Radiology Imaging,

X-Rays,

Radioactive,

X-Photon,

Nuclear Medicine,

CT-Scan,

MRI

Received: February 26, 2018

Accepted: March 15, 2018

Published: April 27, 2018

Physical Principles and Recent Advances of Medical Imaging Systems

Hamidreza Shirzadfar*, Mahtab Khanahmadi

Department of Biomedical Engineering, Sheikhbahaee University, Esfahan, Iran

Email address

*Corresponding author

Citation Hamidreza Shirzadfar, Mahtab Khanahmadi. Physical Principles and Recent Advances of

Medical Imaging Systems. AASCIT Journal of Health. Vol. 5, No. 1, 2018, pp. 21-27.

Abstract

In this paper, a variety of medical imaging systems including Ultrasonography,

MRI, Bone Densitometry, Optical Coherence Tomography, Arthrography, etc. are

reviewed and their advantages and disadvantages are also described. In addition to

these methods, new techniques in medical imaging such as Shear Wave

Elastography and Ultrashort Echo Time are also being reviewed. One of the most

important of these methods is radiology imaging. Radiology is one of a variety of

methods for imaging various parts of the body. Basically, the first assessment of the

patient is radiology. Radiology is a non-invasive and rapid method for diagnosis.

The basis of this method is the ionizer radiation rays. Radiology medicine is divided

into two parts: diagnostic and therapeutic. Radiology medicine based on the energy

used is divided into two types: radiology and nuclear medicine. The basis for the

function of radiology is X-rays and the basis for the performance of nuclear

medicine is radioactive material. Radiology is more dangerous than nuclear

medicine, and is not suitable for pregnant women and children. But radiology is

more accurate and faster than other methods. In addition to its advantages, this

method also includes dangers for the human body. Wilhelm Röntgen was the first

scientist to discover X-rays and record the first radiology image. This paper

describes the components of a radiology device, including a X-ray tube, a

collimator, a detector, and so on.

1. Introduction

Radiology is derived from the word Radius, which means radiation. Ionized rays

in radiology, for diagnosis and treatment [1]. Diagnostic radiology includes

Radiography, Computed Tomography, Mammography and Fluoroscopy, and so on.

Therapeutic radiology is also used for radiation therapy for the treatment of various

types of cancer which includes radiotherapy devices. Electromagnetic spectrum

used for radiology include X-rays, gamma rays, visible light and radio waves. X-

rays can be created by throwing an electron toward an atom [2]. X-rays are divided

into two types, Braking radiation and Characteristic radiation. In Braking radiation,

the electron crosses near the core, and then its speed and energy are changed and

converted to the X-photon. In Characteristic radiation when an electron is thrown

towards the core, it hits one of the electrons and removes it from the orbit. This free

space in the orbit causes energy difference and the release of the X-ray photon [3].

These two types of radiation are shown in Figure 1.

22 Hamidreza Shirzadfar and Mahtab Khanahmadi: Physical Principles and Recent Advances of Medical Imaging Systems

Figure 1. Two types of X-ray radiation [4].

2. Method

In the following, the X-ray generating device, the

radiology device, Nuclear Medicine method and Other recent

of Imaging Methods are described. Also, the advantages and

disadvantages of these methods are also described.

2.1. X-Ray Generating Device

X-ray generating device are different according to their

function. In general, all of them include: X-ray tube (Figure

2), high-voltage generator and control panel.

Figure 2. X-ray tube [5].

One of the important parts of this device is the X-ray tube,

which is an electronic vacuum tube equipped with a cathode

electrode and anode electrode which the cathode is the

negative pole of the tube and the anode is the positive pole of

the tube. The anode is in two forms, fixed and rotating [6].

The fixed type is the Target of Tungsten type which is for

imaging that does not require high power. In the rotating

anode, the Target is a rotating disk of Tungsten type which is

rotated by an electromagnetic induction motor. The reason

for using Tungsten is because it is thermic conductor and has

a high melting point. In an X-ray tube, the cathode infuses

and the electrons are thrown toward the anode, and the

electrons hit the target and X-rays are produced. A high-

voltage generator is designed to produce a potential

difference between the two sides X-ray tube. This part

includes: high-voltage transformer, filament transformer and

rectifier. The control panel is also for controlling the device,

which creates functions for the operator [7].

2.2. Radiology Device

Types of radiological devices include: X-ray tube,

collimator, high-voltage generator, detector, resonator,

control circuit, user's panel and processor device. The

collimator is beam size regulator that has lights and mirrors.

Detector of this device is a radiology film that has a base and

emulsion. These films are an old method for detection, and

today in most countries these images are digitally stored in

databases. Film cassettes have a plate called Grid that is used

to remove irregular beams. The processor is an automatic

device for creating radiology film. Radiological devices are

available in both portable and fixed form. The traditional

radiology has limitations which these limitations include:

time-consuming, high-noise images, low-quality images, and

inability to display at the same time in different locations [8].

Today, with the advancement of technology and the

development of computer systems, two technologies,

Computer Radiology (CR) and Digital Radiology (DR) are

used to detect radiological images. In the CR method, the X-

rays hit a plate of phosphorus, and then read by the scanner

and converted to digital data for computer with the ADC

converter. In the DR method, X-rays hit flat panel detectors,

converted to digital data by an ADC converter, and sent to

the computer for storage. The advantages of these two

technologies, compared to traditional methods, are that they

can be processed before and after recording the results also

have high resolution and high quality images. This

information can be transmitted to other locations by Tele

Radiology system at the same time [9]. One of the most

important uses of radiology is the examination of internal

organs of the abdomen and the digestive tract, diagnosis of

bone fractures, imaging of the lungs, teeth, jaw and face, as

well as the imaging and diagnosis of kidney stones. And also

radiology in therapy to remove tumors and cancer cells [10].

2.2.1. Diagnostic Radiology

Diagnostic radiology for the Diagnosis is a variety of

disorders in the human body, including Radiography,

Computed Tomography, Mammography and Fluoroscopy,

and so on. In radiography, X-rays are exposed to electrical

conditions, and can be diagnosed with various parts of the

body's disease. In simple radiography, external materials are

not required for imaging, but in some cases, the need for

contrast agents is required to detect some tissues.

Consequently, the contrast agents enter the body and then the

imaging is done. In the tomography technique, the X-ray tube

and the detector around the tissue are rotated, then the

imaging is done. Computed Tomography or CT scan,

transmits radiation to the patient's body and is received by

the detectors and convert to the signal and then sent to the

computer. These data are processed by the computer and

displayed. In this method, images are obtained based on the

difference in linear absorption coefficient of the body organ.

Computed Tomography is based on the scan movement, to

different types [11]. Mammography is a method for detecting

abnormal breast changes. In this method, the patient is placed

AASCIT Journal of Health 2018; 5(1): 21-27 23

on the front of the device and the imaging is done. Through

this method, can detect tumors or cancer cells in the breast

[12]. Fluoroscopy method is the simplest method of

radiology. In this method, the patient is placed behind the

fluoroscope and in a short time imaging is done. The

disadvantages of this method are the excessive transmission

of radiation to the patient. This method is used for respiratory

movements of the lung, aperture movements and heart

movements [13].

2.2.2. Therapeutic Radiology

The ionizing rays, by changing the instruction of the atoms

of the human body, causes biological effects in the body.

These rays can also cause cancer and can also treat cancer.

These rays destroy cancerous cells and tumors. These rays

are irradiated relative to the cancerous cell type and the

patient's body physics and measured the amount of radiation

and sent it to the patient according to the required amount

[14].

2.2.3. Advantages of Radiology

The first method for diagnosing diseases is the use of

radiology imaging. This method has a high speed and is very

efficient. This method is very useful in detecting, and the

images that it offers have high contrast and high resolution.

This method is very effective in detecting artery stenosis and

stenting. This method is less costly and easier than other

methods [15].

2.2.4. Disadvantages of Radiology

X-rays produced in this way and radiating to the patient's

body have dangers. These beams are a factor in changing

atoms in the body that cause cancer also cause disorder cell

function. Therefore, this method should not be used too

much. This radiation is very harmful to pregnant women and

causes a genetic mutation in newborns. Therefore, pregnant

women should not use this method as far as possible [16].

2.3. Nuclear Medicine

As previously mentioned, Radiology medicine based on

the energy used is divided into two types: radiology and

nuclear medicine. Imaging is done in nuclear medicine based

on nuclear properties and radioactive materials which the

radioactive radiation used is gamma rays. In nuclear

medicine, visual information is obtained from the metabolic

function of the body. Radiopharmaceuticals used for this

method include isotopes or drugs that are marked with an

isotope. These drugs are injected into the body by

intravaginal injection, subcutaneous injection, oral and

respiration [17]. Instruments used in nuclear medicine

include: Geiger-Muller Counter, Photomultiplier-Tube

(PMT), Absorption Probes, Scintillator Detector, Collimator,

and Dosage Meter. Each of the nuclear medicine devices has

a gamma camera, scanner and electronic circuit X and Y

[18]. Two devices used in nuclear medicine, MRI and CT

scan devices. The methods used for imaging in nuclear

medicine include: (PET) Positron Emission Tomography

[19], Single Photon Emission Computed Tomography

(SPECT), PET-CT, SPECT-CT, SPECT-CT-PET (Figure 3)

and PET-MR.

Figure 3. SPECT-CT-PET imaging system [20].

In the PET method, imaging is based on the detection of

gamma photons created by the destruction of positrons and

electrons. Its function is for neurological diseases and

oncology. Due to the number of crystals and electronic

components, it is more expensive than other methods, and the

number of centers with this method is very few because they

should be alongside an accelerator for isotopes [21]. The

SPECT method is like a PET method, but in the SPECT

method, other radioisotopes are used, and the half-life of

these radioisotopes is higher [22]. The SPECT images show

less detail than the PET method. The SPECT method is less

costly than the PET method, the number of these centers is

high [23]. In the PET-CT combination method, first the CT

scanner is located and then the PET scanner is located. In this

way, 2-dimensional and 3-dimensional images are displayed.

This method is used for neurological diseases, cancer, heart

attacks and epilepsy [24]. In the SPECT-CT method, first the

SPECT scanner is located and then the CT scanner is located.

In this method, the applied information from the SPECT and

the anatomical information from CT are obtained, and then

this information is combined together. In this combination

method, CT data is used to modify the SPECT data [25]. The

PET-MR method, the PET scanner, is located inside the MRI

device, and the imaging is done simultaneously. The pet's

device uses PMT. Because PMT is sensitive to the magnetic

field, in this combination method with MRI, other detectors

are used instead of PMT. These alternative detectors include:

Avalanche photodiode and silicon photomultiplier. The

function of nuclear medical devices includes bone scan, heart

scan, thyroid scan, lung perfusion scan, lung ventilation scan,

and brain perfusion scan [26].

2.4. Other Recent of Imaging Methods

Ultrasonography is one of the most common methods of

imaging. In this method ultrasonic waves are sent by the

probe to the patient's body, and then these waves hit the

target tissue and are reflected and received by the receiver

and an image is displayed on the monitor. This method is

most useful for examining the condition of the fetus, uterus,

and ovaries. This method is safe and does not pose a risk to

the fetus [27].

Bone densitometry is another method of imaging. In this

24 Hamidreza Shirzadfar and Mahtab Khanahmadi: Physical Principles and Recent Advances of Medical Imaging Systems

method, the severity of the bones of the body is measured.

This type of imaging is for people who are exposed to

osteoporosis [28]. Several methods are available, but the

most commonly used method is Dual Energy X-ray

Absorptiometry (DEXA). In this method, two x-ray tubes are

used for radiation to the bone. The higher the bone density,

the greater the amount of radiation absorbed. The beam

received by the detector is transferred to the computer, where

processing and calculation are performed. The reason is the

use of two sources for more accurate measurement. In this

method, two types of environmental scanners and central

scanners are used [29].

Magnetic Resonance Imaging (MRI) is another imaging

method. In this way, instead of X-rays, radio waves and

magnetic waves are used, and therefore they do not pose a

risk to the human body. The patient is placed in a magnetic

field and then the radio waves are emitted to the patient's

body. Then the reflected waves of the patient's body are

analyzed by the computer. Compared with the CT scan

method, this method is purely for imaging soft tissues such as

tendons, veins, nerves and cartilage in the body. But the CT

scan is more commonly used to examine bone problems. In

some cases, the drug is injected into the patient before doing

the imaging. In this method, the patient must remove all the

metal devices because they are absorbed by the magnetic

field. Therefore, people who have implants or pacemakers

cannot use this method [30].

Venography is one of the complementary methods of

radiology that the contrast agents are injected into the arteries

or veins [31]. Then x-rays are radiating to the body. With this

method, blood clots in the main vessels can be detected [32].

Myelography is also one of the complementary methods of

radiology. In this method, the contrast agent is injected into

the patient's spinal cord, and X-rays are irradiated. This

method is used to detect the pressure of the disk on the spinal

cord and the neural roots [33].

In Arthrography, a contrast agent is injected with the air

into the joints and x-rays are radiating to the body. This

method is used to detect cruciate ligament and meniscus

damage and rupture of the rotator cuff shoulder [34].

Shear Wave Elastography (SWE) is one of the newest

methods in medical imaging. Due to the fact that the

elasticity of the healthy and unhealthy tissues is different, it

is possible to detect unhealthy tissues on this basis. This type

of method is based on tissue consistency [35]. In this method,

the liver chronic masses are examined without the need for

sampling and non-invasive. This method can detect the

severity of tissue damage in hepatitis and liver fibrosis. This

method can also be used to evaluate malignant tumors in the

thyroid, breast, and prostate [36]. Diagnosis of fatty liver

with SWE method is shown in figure 4.

Figure 4. Diagnosis of fatty liver with Shear Wave Elastography method [37].

AASCIT Journal of Health 2018; 5(1): 21-27 25

THz imaging is based on terahertz waves. This method has

two fundamental types: Transmission Based and Reflection

Based. This method is used to diagnose skin cancer, breast

cancer and corneal moisture measurement. The Optical

Coherence Tomography method is a cross-sectional

methodology that is the basis of its optical interferometry.

This method creates 3-dimensional images [38].

Another method is Ultrashort Echo Time (UTE). This

method is one of a variety of MRI methods. The echo time is

the time between the frequency radio pulse and the peak sent

in the coil. This is a method for recording lung parenchymal.

Using this method, it can display complete lung anatomy and

detect pulmonary disorders. This method is without ionizing

radiation, so there is no danger and is therefore more

appropriate than CT scan [39]. This method creates 2-

dimensional and 3-dimensional images [40, 41]. The image

taken from the lungs, at different echo times, is shown in

Figure 5.

Figure 5. The image taken from the lungs with UTE method, at different echo times [42].

3. Result

Initially, a radiology device, including a X-ray tube, a

collimator, a detector, a high-voltage generator, resonator,

etc., was described. The X-ray generator is responsible for

producing x-rays using two anode and cathode electrodes.

The collimator also adjusts the size and radius of the beam

and radiology films are detectors of this device. Radiological

device in diagnostic and therapeutic fields. Radiology is

harmful for the human body because of the use of X-rays, but

more accurate and faster than other methods. In nuclear

medicine, imaging is performed based on nuclear properties

and radioactive material. Also, Instruments used in nuclear

medicine include: Geiger-Muller Counter, Photomultiplier-

Tube (PMT), Absorption Probes, Scintillator Detector,

Collimator, and Dosage Meter. Imaging based on nuclear

medicine involves various methods that each of them has

different advantages and disadvantages.

4. Discussion

Radiology method is based on X-rays and a nuclear

medicine method based on radioactive material. Radiology is

very dangerous for pregnant women due to the use of

ionizing radiation and causes a genetic mutation in the fetus.

The methods used for imaging in nuclear medicine include:

(PET) Positron Emission Tomography, Single Photon

Emission Computed Tomography (SPECT), PET-CT,

SPECT-CT, SPECT-CT-PET and PET-MR. An

Ultrasonography method is based on ultrasound that enters

the body by the probe. Bone densitometry is used to measure

the degree of bone hardness that is based on X-rays. The

MRI imaging method is based on magnetic field resonance s

that do not have the harm caused by ionizing radiation. In the

Shear Wave Elastography method, based on the elasticity of

the tissue, it can detect unhealthy tissue that is most

commonly used for liver disease. Ultrashort Echo Time is an

MRI imaging technique used to record parenchymal lung.

26 Hamidreza Shirzadfar and Mahtab Khanahmadi: Physical Principles and Recent Advances of Medical Imaging Systems

5. Conclusion

In this paper, types of imaging methods have been

investigated. One of the most important of these methods is

radiology imaging that is faster and more accurate than other

methods. But this method has some disadvantages due to the

use of X-rays. This method is very dangerous for pregnant

women and children. In nuclear medicine, nuclear properties

and radioactive materials are used. Radioactive material is

also harmful to the body, but its intensity is less than that of

X-rays. Methods that are based on the Magnetic field

intensification spend more time than the radiological method

but do not have the dangers of ionizing radiation. In this

method, all metal objects and objects that are sensitive to the

magnetic field should be away from the patient at the time of

imaging. These imaging methods are diagnostic and

therapeutic. These imaging methods are invasive and non-

invasive. Some imaging techniques require contrast agents to

display the tissue properly. All the methods described have

advantages and disadvantages each of which, according to

their function, are used in various diseases.

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