Use of computer in x-ray machine imaging

The digitization of the x-ray film image into electronic storage files involves the use of computer. The use of computer in diagnostic modalities provides an efficient basis for data reduction. With the aid of a microcomputer, one can generate a wealth of information concerning the pertinent body and the organ under examnation and is very help to know its medical characteristics. Methods of computer-aided digitization of x-ray images is very efficient. Advances in medical knowledge and technology have created new opportunities for disease specific diagnosis and treatment. The complexity of medical data at various levels of resolution has increased the need for system level advancements in clinical decision support systems that provide computer-aided analysis for diagnostics and treatment. The development of a computer-aided diagnosis (CAD) system for mass detection using advanced computer vision techniques that will be trained with retrospectively detected cancers on prior mammograms is very helpful. classify computer detections into three groups: malignant lesions, benign lesions, and false-positive computer detections. a computer-aided diagnosis system for breast cancer by combining the following three data sources: mammogram films, radiologist-interpreted BI-RADS descriptors, and proteomic profiles of blood sera.

Digital X-ray Machine

The traditional X-ray machines are expected to reduce in use as many large companies introduce new X-ray systems that replace x-rays films with sophisticated electronic images.
This change in radiology by the electronic revolution is pity nicer, for the simple reason that the pictures taken by X-ray film are so large and these may be in the range of 8 by 10 inches up to 18 by 24 inches of finely detailed images. But computers can finally handle the tens of millions of bytes of data needed to make and manipulate such big pictures.
The pictures produced by X-ray film or by digital x-ray machines (digital plates) appear at first glance to be roughly the same. Both of the images are produced when a stream of X-rays is shot through the body onto a sheet of film or a digital box. But with the radiographic films, the picture cannot be seen until the negative is developed, which usually takes at least a couple of hours in a busy hospital, and once taken, the image cannot be manipulated to enhance one part of the image at the expense of another. The huge film negatives must be stored in great film library rooms and shipped by mail or messenger to be viewed by other doctors.
Because digital information is inherently more flexible than an image embedded in a piece of film, therefore it will be some immediate advantages to digital X-rays. In both cases, the X-rays are absorbed by dense tissue, such as bones, so few rays get through to darken the film. Thus bones show up white. X-rays are not absorbed as much by tissue such as muscle, so the rays get through to make dark gray areas on the picture.
The main difference is how the X-ray patterns of white and gray are turned into images. Using film, chemicals in the emulsion darken when hit by X-rays. In digital systems, a chemical layer of cesium iodide first absorbs the X-rays and gives off light, then photodiodes made of amorphous silicon pick up the light and give off corresponding electronic signals that light up pixels on a video screen.
Parts of a Digital X-Ray Machine:
The digital X-Ray machine consists of an X-Ray tube and driver to source X-Ray. The X-Ray passes through the patient's body and the digital camera (located on the other side of the patient) captures the resulting image. The main base station controls the X-Ray tube, analyzes the image and displays the image on the CRT.
Digital Camera:
The digital camera converts the received image into digital signal and transfers the digitized image to the base station through a fiber optic link.
Main Base Station
The functions of the main base station includes Drive and control the X-Ray tube,Communicate with the digital camera system through Fiber, Store the pictures on the hard disk for image retrieval and processing, Interface to an operator console for overall system control and image manipulation, Analyze and enhance the image stored on the hard disk and display the enhanced X-Ray image on a CRT monitor.

The LatticeSC/M (System Chip/MACO) family of FPGAs combines a high-performance FPGA fabric, 3.8Gbps SERDES and PCS, 2Gbps Parallel I/Os, low-power 1V Vcc option, large embedded RAM, and embedded ASIC blocks to provide the highest performing FPGA in the industry. LatticeSC family delivers best in class solutions for high throughput standards like Ethernet, PCI Express, SPI4.2 and high speed Memory Controllers. LatticeSC is equipped with embedded memory, hierarchical clocking and clock management resources for high-end system designs. For low-cost, system-level integration, the LatticeSCM family offers MACO (Masked Array for Cost Optimization): up to 12 embedded structured ASIC blocks per device with a variety of pre-engineered IP blocks.

Linear Tomography

Tomography is a method of viewing a slice through the body. (Greek Tomos - slice).
In Linear tomoghraphy source of x-rays and film of x-rays moved in opposite directions at the same speed. Any point in the image plane will appear in the same position on the film. All other points image at different positions on film as source and film are moved and thus image blurred (e.g. point closer to source than image plane - dotted lines indicate path of X-ray photons). Depth resolution of approx. 1 mm possible. If the movement runs parallel to an elongated body structure (e.g. femur) there will be comparatively little blurring of the long edges even when not in the pivot plane. A circular instead of linear movement can help in such cases. Consider a rod connecting source (S) and film cassette (F), with pivot, P, at a variable point as in diagram. The slice through body in focus changes as pivot moves up and down. The thickness of the cut is controlled by the size of tomographic angle θ. The greater the value of θ the thinner the slice will be. This is because even structures very close to the pivot are blurred, since their image moves significantly on the film. If θ=0 it is a conventional radiograph.

Relative importance V and I in medical imaging

The x-ray tube characteristics and control parameters have significant importance in inquiring medical images.
· Contrast decreased as incident photon energy is increased
· Best contrast is found due to photoelectric effect which is function of atomic number z and directly proprotion to cube of z
· Scattering of electrons in x-ray tube causes image blurring
· High energy attenuation of electrons causes damage in quality of image and it may be due to ionization and over heating in x-ray tube
· It is normal pratcice that 20 - 100 keV used for diagnostic radiology in this range photoelectric effect and Compton scattering is pronounced.
· Greater than 100 keV are used when contrast between bone and surrounding structure not required (e.g. imaging lungs)
· High Z elements may be used to improve contrast e.g. injected NaI to investigate circulatory system or barium sulphate in gastro-intestinal system

voltage, current and Target material in X-ray tube

The x-ray tube voltages, current and Target material are very important in production of x-rays from tube, by changing these or one of them can change the quality and quantity of x-rays production. Here we will discuss the Effects of voltage, current and target material on x-ray spectrum one by one.
With the increase in x-ray tube voltages V, following effects are pronounced:
· spread of wavelengths increases
· intensity increases (as the total intensity is directly proportional to the square of V)
· peak in intensity shifts to higher energy side

When the x-ray tube current i is increased, following effects in other parameters of x-rays are noticed:
· rate of production of electrons at the cathode is increased
· intensity increases (because total intensity is directly proportional to i)
· maximum energy of x-rays remains unchanged
· intensity profile of x-ray beam remains the same

Changing the target material changes the atomic number, Z, so the following things can suffer from it.:
· x-ray intensity changes - the probability of a collision also changes because intensity is directly proportional to Z
· changes the characteristic lines of the x-ray spectrum because these lines are function of number of electrons, in shortly speaking, the atomic number of Target material Z.

Tungsten (Z = 74) is widely used as a target material because it has reasonably high Z number, and high melting point (3650 K)

Leakages of x-rays and Warning label

The control panel of an x-ray machine contains the main power supply switches, controls of different parameters, so it must be bear with the warning statements for example:
“Warning: This x-ray unit may be dangerous to patient and operator unless safe exposure factors, operating instructions and maintenance schedules are observed.”
X-ray control means a device which controls input power to the x-ray high-voltage generator and/or the x-ray tube. It includes equipment such as timers, phototimers, automatic brightness stabilizers, and similar devices, which control the technique factors of an x-ray exposure.
The leakage x-rays from the diagnostic x-ray machine and assembly be measured at a distance of 1 meter in any direction from the source must not exceed 0.88 milligray (mGy) air kerma (vice 100 milliroentgen (mR) exposure) in 1 hour when the x-ray tube is operated at the leakage technique factors. Compliance shall be determined by measurements averaged over an area of 100 square cm with no linear dimension greater than 20 cm.

Prepare history of patient with Care

Radiologist and x-ray technision must take care the patient with having history of patient or ask following question prior to expose the patient for an iamge.
Is the patient pregnant?
Do the patient have any allergies?
What medications do patient take?
Do the patient have any pre-existing conditions such as heart, blood, or kidney disease or diabetes?
What symptoms have the patient experienced recently?
History of any type of surgery of the patient ?

Dangers and Risks with X-ray machines

Human being have five sense by using them our judge and have notice about the things around us. But in the case of x-ray (type of ionization radiation) we can not find it. In contrast to heat, light, food, and noise, humans are not able to see, feel, taste, smell, or hear ionizing radiation. The only way to find them is the use of proper radiation monitoring equipments. Without the use of detectors we can know about the presence of x-rays like other radiations. So there are a lot many risk and dangers associated with x-rays in terms of radiation dose. The major sources and cause of danger are due to unnecessary exposures both to patients and to the radiation technician are discussed below.

1. The primary beam of x-rays generated from x-ray tube is the most hazardous as it could be a source of direct high exposure. The Exposure rates at the port or opening of x-ray tube may be in the order of of 4 exp5 R/min.
2. The Leakages and scatter of the primary beam through cracks in ill fitting or defective equipment is also a high source of exposure and sometimes it can give a very strong beam of high intensity.
3. There are hazard resulting from the penetration of x-ray beam through shutters or tube housing. Adequate shielding is necessary to minimize theses leakages and proper design is unavoidable in such cases with concrete and lead walls, leaded glass, and plastic movable screens .
The effects of x-ray exposure depends upon the duration, time of total exposure, acute dose, energy of x-rays interms of high voltages applied to machine, intensity of x-ray beam interms of mAmps applied to x-ray machine, which part or organ of body is exposed, and Total Dose.

What are the basic uses of Tomography

The Tomography is actually a type of image processing and image acquiring technique which gives a better cross sectional view of an obeject without cutting it into pieces. The image produces is called a tomogram. A Tomogram shows a single plane of an object in very specific detail sometimes one can find that kind of detail with other conventional techniques or modalities. Usually people take tomography only for the use of medical imaging. Yes, tomography is mainly used in medical science, but it is not the whole story, Tomography is used in various fields of science and engineering. In medicine it is used to create a cross section of the body to reveal underlying medical conditions. similarly other branches of science also utilize tomography, including biology, geology, oceanography, archeology, and materials science. In archeology, Tomography is used to ensure the integrity of specimen under examination or research. Geologists use it to look at cross sections of rock and other materials. Tomogram can be taken by the use of a number of different rays including X-rays, gamma rays, ultrasound, magnetic resonance.

How to reduce blurr in images

Body section radiography is a special x-ray technique which can be used to reduce the blurr in the shadows of superimpose structures to show clear view of principal structure under examination. It is important to learnt that this is not a technique to improve the sharpness of the radio-graphic image, but it is a process in which blurr of the image can be controlled (reduced). In the start of this process in very periods various names were adopted for it, but in 1962, the International commission on radio-logic units and measurements give it a name "TOMOGRAPHY", which includes all types of body sectional radio-graphs. Tomography is referred with follows well known names:

1. Tomography ; tomogram
2. Planigraphy ; planigram
3. Stratigraphy ; stratigram
4. Laminography ; laminogram

The main elements used in tomography are an x-ray tube, an x-ray film, and a rigid connecting rode which can rotate on a fixed fulcrum. The main idea behind tomography is that when x-ray tube moves in one direction, x-ray film moves in other direction (opposite to tube). Fulcrum is the only point in this system which remains stationary in whole the process. The tomography angle is the measure of amplitude of x-ray tube calculated in degree. Some times it is also called arc of tomography.

Imaging characteristics of Intensifier

Contrast:
Contrast is the brightness ratio of the periphery to the center of the output screen. The typical contrast ratios are 10:1 but 20:1 is more better, it can vary and depends on the manufacturer to manufacture. there are two factors tends to diminish contrast in image intensifiers.

1. The input screen does not absorb all photons in the x-ray beam, rest of them produce a background of fog that reduces the image contrast.
2. The retrograde light flow from the output screen. Normally the major component of retrograde light flow is blocked by the use of a thin layer of aluminum on the back of the screen. If the thickness of aluminum layer is not very thin then electrons can strike with it and photon emitted due to will again produce "fog".

Lag:

Lag is the persistence of luminescence after the x-ray stimulation is 'switched off". Its maximum value in old age machine was in between 20 to 30 msec.

Distortion:

When electric field is applied to focus the photoelectrons on output screen, all electrons donot behave according to needs. Some peripheral electrons donot strike the output screen where they ideally should. The result is an un-equal magnification which produces peripheral distortion. the same effect is observed in optical lens and termed as "pincushion effect". This distortion makes difficult to evolute the straight lines. Unequal magnification also causes un-equal illumination. A fall-off in brightness at periphery of an image is called "Vignettimg".

The centre of the image intensifier screen has better resolution, a brighter image, and a less geometric distortion.

The design of image Intensifier

When an x-ray beam passes through the patient, it enters the image intensifier tube. The main components of the tube are as follows:

1. Input Phosphor and Photo-cathode
2. Electrostatic focusing Lens
3. Accelerating Anode
4. Output Phosphor

Working Principle of an Image intensifier screen

The input fluoroscopic screen absorbs x-ray photos and converts their energy into light photons. these light photons strikes the photo-cathode to emit photo-electrons. A high potential difference is already applied which immediately drawn away these photo-electrons away from the photocathode. On the way towards anode these photoelectrons are further guided with the help of focusing electrostatic lens toward output fluorescent screen without having distorting their geometric configurations. On reaching the output screen the photoelectrons strikes on fluorescent screen to emit photons which form fluoroscopic image to the eyes of observer.

In short, the image is first carried out by x-ray photons, then by light photons, next by electrons, and finally by light photons in an image intensifier screen.

Fluoroscopic imaging in old age

Initially the fluoroscopic images were made with the use of x-ray tube and fluoroscopic screen. The material of fluoroscopic screen was copper activated zinc cadmium sulphide that emitted light in the yellow green spectrum. This was the reason why the term "green screen" came as a synonym for fluoroscope. For protection purposes of eyes of radiographers a lead screen was also used because they normally have direct stare into the screen. Before viewing the image on the screen radiologist make his /her eyes dark-adopted by wearing red goggles for 30 minutes prior to examination as the fluoroscopic screen were very faint. All these practices are obsolete now with the invention of image intensifier design.

X-Ray Film processing

There are many steps involves in image formation on an x-ray film, some of them are briefly discussed here. The light sensitive material in the emulsion is silver iodobromide crystal. Light exposure causes the grains in the emulsion to develop into an invisible latent image.
Development:
Development is a chemical process in which the latent image on film is amplified by a factor of millions to make a visible silver pattern. The basic chemical reaction in this process is reduction of silver ions. The developer is reducing agent. Time is fundamental factor in developing process. Normally now the developing solution contains two developing agents, Hydroquinone plus Phenidone or metol. The bromide ions released by the reduction of silver ions pass into the developing solution limits the life of developing solutions.
Fixing:
The silver halid in emulsion donot completely reduce to silver during developing process, rest of silver halid is removed from the film without damaging the image on the film.Thiosulfate in the form of sodium or ammonium salt is the common fixing agent. This is also called hype because early ages of nomenclature, the name given to Sodium thiosulfate was 'Hyposulfite of soda' and its short form become "hypo" for photographers. To decrease the swelling of gelatin, chromium or aluminum compound are used in addition to thiosulfate in fixing solutions.
Washing:
After developing and fixing the x-ray film is watched with water. With the passage of time x-ray film turns to brown, this is because of incomplete washing. In Incomplete washing of x-ray film the retained hypo reacts with silver of image to form brown silver sulfide.

double emulsion x-ray film

Cross sectional view of a double emulsion x-ray film

Physical characteristics of xrays Film

When an x-ray beam reaches the patient, it contains no information regading the patient body or tissue or organ etc. After passing through and having interaction with the tissues in the body of patient, it contain that information which a radiographer wants to know about. On this stage we are unable to get any viw from it unless until we transfer that information to suitable medium of veiwing by human eye. In normal practice, the most common method use to decode this information in attenuated x-ray beam is a ' photographic film'. This process involves, the energy of x-ray beam is converted into light by intensifying screens and this light is then used to expose the films.
Radiographic Films:
The x-ray film is photographic film consisting of a photographically active, or radiation sensitive emulsion that is coated on both sides of a transparent sheet of plastic which is called base sheet or simply base. A thin layer of adhesive material is used to make a good contact between film base and emulsion. Again some supercoating layers are used to protect the mechanical damage of emulsion which is delicate. The purpose of film base is to support the fragile photographic emulsion. The important characteristics of the film base are as follows:

1. It must not produce a visible pattern or absorb too much light when the radiograph is viewed.
2. The flexibility, thickness and strength of the base must allow for ease of processing or developing.
3. The base must have dimensional stability, the shape and size of the base must not change during the developing process or during storing.

Original x-ray plates are consisted of a glass plate with the emulsion coated on one side. The two most important ingredients of a photographic emulsion are gelatin and silver halid. Emulsion thickness varies with film type which in not thicker than 0.5 mil.

Luminescent Screen and Intensifying Screens

The x-rays Photons making the image on radio-graphic film can not be seen from human eye. The information passing through is converted to image by following methods;

• A Photographic emulsion can be exposed to x-rays directly,
• The energy of x-rays is converted to visible energy spectrum, and that light may be used to expose the films or this light can be view directly.

Fluorescence:

Luminescence refers to the emission of light by a substance by any kind of stimuli for example light, chemical reaction, ionizing radiation etc. But Fluorescence is a kind of Luminescence when light is emitted instantaneously. Fluorescence is used in radiology because the fluorescent material mostly inorganic crystal has ability to emit light when it is exposed to x-rays. with such kind of materials image intensifying screen are fabricated. The main purpose of these are to reduce the x-ray dose to patient and get the maximum results and a best image. The x-ray films used in intensifying screen has photosensitive emulsion on both sides.

In early seventies, Calcium Tungstate was used as phosphor in most of the screens, later own new other phosphor were also used to make the film faster, there are three main methods to make a screen fast,

• Thicker phospher layer
• High conversion efficiency of the phospher
• High absorption Phosphers

CaWO4 screen speed is mostly measured by the thickness of the phosphers.

Exposure Timer

There are many ways to control the lenght of exposure from x-ray machine. But the basic types of exposure timers are as follows:

1. Mechanical Timers
2. Electronic Timers
3. Automatic exposure control
4. Pulse counting Timers

Mechanical Timers:

The mechanical timers are very oldest kind of timer used to control the length of exposures. They have a mechanical setup and switches which were used to make and break the electrical connections of high voltages between electrical generators and that of x-ray tubes. They are now rarely used.

Electronic Timers:
The electronic timers are normally based on a RC circuit. The lenght of exposure is control by the charging and discharging of capacitor through a resistor. The time period required to charge this capacitor can be varied by varying the value of the resistor. Thus a capacitor with variable resistor and associated electronic circuit was enough to select a specific time of exposure.

Automatic exposure control or Photo Timers:
The automatic exposure control or photo timers are made to reduce the human error in the calculation of exposure time, as an operator can only guess the thickness of tissue by measuring the patient's thickness. But it could be incorrect. In Automatic control exposure technique, first high voltages are selected then mAs are selected according to the need of exposure. The heart of this method is a device which can detect the radiation and can give feedback to x-ray machine in the form of current for appropriate selection of parameters. There are three such devices that could be used for this purpose.

1. Photomultiplier detectors
2. Ionization chambers
3. Solid state detectors

X-ray Generators

An x-ray generator is the device that supplies electric power to the x-ray tube. The x-ray generators modifies the electric supply to the needs of the x-ray tubes. The x-rays tubes need electric supply for two reasons.

1. To boil out the electrons from the filament
2. To accelerate these electrons towards anode to produce x-rays.

Thus x-ray generators must have two basic electric sections and circuits to supply the electric energy to filament and to electrodes, they are called filament circuit and high voltage circuit.

Also most of the generators include a third circuit for the timer, which control the time of exposure to take an image.

The mechanism of the generator is , it have two main parts, a control panel or console and a transformer assembly. The control panel allows the operator to select appropriate Kvp,mA, and the exposure time for a particular radiographic examination. There is some suitable metering on the console to indicate the selection and actual values of all parameters. There are a button with two levels, one start the heating of filament and other start the exposure.

The other part of x-ray is transformer assembly which is a grounded metal box filled with oil. It contains a low voltage transformer for filament and a high voltage transformer for the high voltages. An important part of this section is a group of rectifiers for the high voltage circuit. The potential difference in these circuit may be in the range of 150,000V. Due to this high level of voltages, the transformer and rectifiers are always immersed in oil. This oil serve as an insulator and prevent sparking between various components.

The anode of the X-ray Tube

Anodes are positive electrodes of x-ray tubes and these are of two types:

1. Stationary anode
2. Rotating anode

For simplicity point of view lets discuss stationary anodes first. Moreover they are basic and conventional, many of its principles are also applied in other types of anodes.

Stationary anode:

A tungsten plate of usually square or rectangle in shape of 2-3 mm thick embedded in a large mass of copper forms the basis of stationary anode. The choice of tungsten material is due to several reason, some of them are listed below.

1. It has a high atomic number (74), which is more efficient to produce more x-rays,
2. It has high melting point 3370 C, so can sustain at high temperature.
3. Tungsten is a reasonably good material for the absorption of heat.