Equipment FeaturesMobile X-ray equipment is equipment which can be moved from one place to another and used at the patient’s bedside, as obvious solution to providing facilities

for: 1 -In-patients who could not leave their beds, especially those who cannot be

moved away from their ward.2 -Surgeons who required X-ray control guidance during the course of their work in

the operation theatre.

These days may bedridden patients in need of radiography are now transferred safely from their ward to the imaging department, where they can be examined with

all the efficiency that the department can offer .These facilities include full radiation protection: for the patient, of course, but also for other personnel who otherwise, in the hospital ward, could have bee at risk.

Therefore their use should be restricted .

Despite these points, the service of mobile X-ray equipment can be in demand all day especially in a busy hospital and with complicated stution patient. Study of the principal features of their construction and operation is necessary, as always, for

correct and safe use .

X-ray Equipment:

Units fall broadly into two groups:1-Portable Units.

2-Mobiles Units.

The broad distinction between the two being the difference in power output and the ability to transfer equipment .

Portable units are small and light in weight, which normally can be dismantled and carried, usually by one person, and have relatively low radiation output ,

while Mobile x-ray units are bigger and heavier than ‘Portable’ units which is movable but because of its weight and size can only be wheeled along flat surfaces to place where required, they are usually have higher radiation output.

Portable units feature: Advantages :

1 -light weight. 2- Standard power supply. Disadvantages :

1 -Low output. 2- Lack of stability. 3 -Lack of precision.

Components: 1- Oil-Filled lead lined tank:

In order to make the equipment simpler, lighter, less expensive and easy to carry, it is usually constructed with:

a-X-ray tube Self-rectified. Stationary anode .

B- High-tension transformer.C-Filament transformer.

This is described as a tank construction and the whole enclosure is called the tubehead.

2 -A small control unit: It has;A-Rheostats: to vary the mA ad kV.B- Timer (S). C- Exposure switches.Output: The maximum output is usually 80 kVp and 20 mA.

.Mobile units feature: Capable of being moved ethier manually or motorized drive.

Advantages :1-great stability .2 -high output .

3 -wide range of kV and mA selection.4-the control panel and the high tension generator (with full-wave rectification) all are

carried by strong machine base, away from the tube which have an advantage to greatly increased the x-ray output.

5-Has a rotating anode.6-Flexiable tube movment.

Disadvantages :1 -heavy in wieght .

2 -needs espeical maintanance .

Output: Up to 300 mA and maximum of 125 kVp.

. Mobile units Classification:They are classified by two ways:

. By output:1.Low power mobiles : these operate at max. x-ray current (mA) of 10 to 30 with a range of 40 to 90 kVp. Example: Dental, war x-ray equipment.1.Average power mobiles : these operate at a range x-ray current (mA) of 50 to 60, 100 to 150 mA with a range of 40 to 90 kVp, 95 kVp. Example: for skull, limbs.3- High power mobiles : these operate at max. of 300 mA, at a max. 125 kVp. Example: for CxR, abdomen, skull, pelvimetery, IVU, pediatrics.

. By power supply:

1.Main supply equipment. 2.Capacitor discharge equipment.

3.Battery powered equipment.

Main-Supply equipment .Advantages & disadvantages:

Energy may be drawn for X-ray exposure directly from the mains voltage supply. This is convenience if there is no need for the energy to be carried around within the mobile unit. But cable resistance and supply variation at different locations where the unit is used can raise difficulties affecting image quality.

Special Features: This kind of equipment must have a robust connection cable. This encloses 3

low resistance conductors, each with a relatively large cross-sectional area. Two of the conductors carry the current, which the generator draws when an

exposure is made. The third provides a safe, reliable connection to earth .

The cable must be long enough (2 meter) for equipment to be used in most locations.

. Advantages & disadvantages:

1. Small in size and light in weight, because there is no H.T.T. 2. This unit has the advantage of storing energy in the form of electric charge for later

use for X-ray exposures. Therefore, it can be used in places where there is no electricity, or no a convenient mains outlet socket, or there is electrical power but not adequate

(not enough to operate the X-ray unit), or suffers ‘drops’ in its values.3. The unit has the advantage of providing high X-ray output (usually high mA). The

given kVp is from 30 or 40 up to 100 to 125 kVp and 500 mAs.4. Shorter exposure time.

5. It has no timing control device since only the kVp has to be selected, so the mAs depends on the kVp. As the kVp in the capacitor discharge falls the mAs does so. 6. Simple in operation, it can be supplied by any voltage from 60V to 220V (so we

shouldn’t worry from voltage fluctuation).7. Provides consistently reliable output and results (uniform wave).

8. Capacitor discharge is usually limited so that the drop in kVp is only 35% on heavy exposure.

9. The disadvantage that it has is the limitation in exposures. Few times of exposure needs capacitor charge.

Capacitor discharge equipment

.The work of the capacitor:

)Charging stage( :After the radiographer connect the unit to the mains and selects a kVp value, the switch operated to charge the capacitor to the required kVp (G1 & G2 will be connected), via the high tension generator, then the capacitor acts as a store or source of energy.

)Discharging-exposure stage :(by pressing the exposure switch the X1 & X2 will be connected then the capacitor will discharges electrons through the X-ray tube and produce X-ray exposure.

Primary C ontrol

Generator C ircuit

C apacitor C ircuit

X-ray Tube

G1

X1

G2

X2

Ready

C harge

X-ray

.Special Features:

1-Charging circuit contains solid-state rectifiers (selenium types) and capacitors these two acts as energy storing elements and as voltage multipliers (raise voltage to higher kV values, instead of the high-tension transformer).

2-The size of the capacitor determines the maximum output (mAs); this is called Capacitance Value (C.V.). For example; if the typical C.V. for charging capacitor is 1.0 the typical mAs are between 0.4-60 mAs. After every exposure we do the mAs will be reduced.

3-Its tube has rotating anode and grid-controller.

Battery-powered generator:

This is called also cordless mobile unit . This unit use batteries as a source of energy for X-ray exposure.

Advantages:1-This machine can be used freely, provides wide range of satisfactory kVp & mAs.

2-This machine could be recharging less frequently that the capacitor one. Some machine allows you to take up to 500 exposures without re-charging.

.Disadvantages:

It needs special care and maintenance.

.Special Features:This kind of machine usually uses 2 batteries of car kind 12V . All batteries are sealed for safety. Charging is achieved by connecting the generator to the mains at times when it is not required for radiography. These batteries are also used as a motor for the unit wheels that makes the driving of the machine much easier. The batteries need regular care and maintenance. If the machine is well maintained, it could last up to two years of their working life. This care and maintenance includes:The unit should be left connected to the mains power supply of (200v or 115v) :

–Every night. – During weekends . –At all times when the unit is not being used.

Naked flames or lighted cigarettes should not be held near the batteries when they are being charging up (because of the risk of the hydrogen gas explosion).

The acid level in the batteries should be checked every 2 weeks. Its proper recommended level is 6.0 mm. If the level drops below this, distilled water (only) must be added.

Mobile Image intensifier units“C” arm unit:

Mobile image intensifiers are designed primarily for use in any case needs screenig image or immediate X-ray visualisation especially in:

a- The operation room with:Orthopedic patiets (for reducation and fixation of the fractured femoral neck).Urinary cases (e.g. remove renal calculi).Biliary system cases (e.g. remove gall stons)

b- The intesive care departments For:

1-Introducation of cardiac catheters.2-Implatation of cardiac pace-maker.

.Advantages:1-Immediate localization and manipulation of fractures, calculi ad catheters under

direct vision.2-Fewer radiographs are needed to provide the required information, so a

reduction in patient and operator radiation dose will occur.3-Reduced operation time can be achieved, which requiring less anaesthetic and

more efficient use of theatre operating time.

.Disadvantages: Very close control must be kept on the length of fluoroscopy which should be

kept as minimum as you can to avoid accumulating dose. The methods used to limit the exposure time include:

1-The use of fluoroscopic time display and alarm. 2-The use of pulsed fluoroscopy.

.Equipment Special Features:1-The tube head (X-ray tube & collimator) is mounted on the end of the “C”

shaped arm. The X-ray tube has a dual focus, commonly 0.6 mm for fluoroscopy and 1.2 mm for radiography. It has two collimator, one to restrict the beam size to the intensifier input phosphor size, and the additional one to collimate X-ray field size.

2-Image intensifier & TV camera are mounted on the opposite end of the “C” arm .3-The “C” shaped supported arm is mounted on a vertical column to provide:

a-Vertical movement. b-Rotation about the fixing to allow a vertical or horizontal beam to be used, or

angles between.4-The vertical column is mounted on the mobile base. The mobile base carries the

control unit and the H.T generator behind the vertical column, thus making use of its weight as a counterbalance for the ‘C’ arm. All movements of the column must have secure mechanical lockers. The wheels on the base must be large to allow easy movement.

5-TV monitor trolley: A separate trolley carrying the TV monitor which required so that the monitor image can be viewed from the most convenient position for the operating surgeon.

6-Power supply: 13 Amp 240-volt main. For fluoroscopy a maximum of 3 mA is provided, for radiography 30-40 mA with a kV range of 50-90.

.Methods of recording the image:

1-by video-tape to record the moving images.2-by radiography either by the cassette holder, which provided on the face

of the intensifier, or by storing images during fluoroscopy and transfer it to X-ray films.

NOTE: Care must be taken in setting up this equipment to ensure that the X-ray

tube is as far as possible from the patient to minimize the patient dose especially patient’s skin; If the focus-skin distance is short the dose received by the patient will be high and the image quality will be poor which occur because of the high object-phosphor distance and enlarged image.

Work with ‘C’ arm Equipment in the Operation Room:

Undertaking radiography in conditions other than the controlled ones of the X-ray department has a psychological effect on the radiographer especially in the operation theatre. This work has an emergency nature, and the time factor is important. The aim usually in surgical procedures is to be as quick as is consistent with efficiency; the prolonging the length of time during the patient is under anesthesia will increase the patient risk, so the radiographer should be calm and fast. Using X-ray machine in the operation room involves three risks:

1-Risk of importing infection into the operation theater from other places in the theater or in the hospital. Cleaning the machine surface before and after usage by sterilized or antiseptic solution in alcohol base can reduce this risk; this unit can be cleaned easily because of its manufacturing feature. The other way of reducing this risk is by placing a plastic cover on the places of the unit that may touch the sterilizing area during every procedure.

2-Risk of explosion this risk could occurred by using ignitable anesthetic gases during exposure which

sometimes produces sparks, these sparks could be produced from the unit wheels or from the electrical parts of the control panel. This risk had been eliminated by:a- Using non-ignitable anesthesia gasses.

b- Special conducting wheels. c- Special spark-proof X-ray units and electrical plugs are used.

3-Radiation risk to everyone in the theatre. The radiation protection is the responsibility of the radiographer before starting any

exposure. This can be reduced by:a-Wearing lead apron and TLDs, radiographer and the staff in the room must wear lead apron either during fluoroscopy or during taking radiographs.

b-Using the inverse square law with staff by standing at maximum distance and outside from the path of the radiation source.

c-Collimation the radiation beams on the required area of the patient. d-Minimize the screening time as possible as you can.

e-Giving clear instructions to staff before any exposure is made.

Special concerns:

1-In many modern theatre suites it is normally that you find a special room for the X-ray equipment and for processing facilities. The first thing that the radiographers must be concerned with is their own personal preparation before entering an aseptic controlled area. The radiographer should change cloths and wearing the theatre uniform and wear (Shoe cover, hair cover, mask and washing hand).

2-Before a unit is removed from its store and after it is placed in the theatre, it should be tested. This procedure should be done before the surgical procedure .

3-The processing equipment should be switched on and tested .

4-All needed accessory equipment should be available (e.g. cassette holder).

5-Always the examination request should be checked before starting the preparation.

Work with Mobile Equipment in the Ward:

General concerns:Examinations are normally complicated by a variety of situations, which include:a-The patient’s medical condition; degree of consciousness and cooperation.b- The patient’s treatment restrictions:

1-Life support system.2-Drips (I.V. line).

3-Chest or abdominal drains.4-ECG.

c-Physical restrictions : 1 -Room size and layout.

2 -Equipment size and shape. 3 -Access to adequate power supply.

Special concerns:

The first step towards success is:

1-Fully understanding of the received request, so that the exact nature of the X-ray examination and the reason for it are both understand.

2 -Correct equipment and cassettes (cassette size, speed and number) are obtained, to avoid unnecessary delay and disturbance.

3-With serious illness patient the radiographer should ask for in-charge nurse or medical staff help, to avoid unintentional patient’s injury or mistakes.

Standard Procedure for Success Result:a- When the radiographer arrived to the patient ward he should first report to the nurse in-charge, this will enable the radiographer to find out in which part of the ward is the patient to be X-rayed and examination to be done. This also enables the radiographer to explain the procedure to the nurse and receive any special patient’s concerning information, which will help the radiographer to assess any further help.

b- It is kindness for the radiographer to go in to see the patient without the equipment and with smiling approach, to give the patient explanation of what is to be undertaken. This few minutes has a great effect on removing the patient’s fear and achieving full cooperation, this is also will enable the radiographer to assess the patient’s capability for cooperation and any physical difficulties presence.

c- Now the radiographer should place the equipment in an appropriate place, then the cassette should be placed with help and care. The tube should be positioned and a radiograph is taken.

d- The radiographer should preserve the patient’s privacy by pulling around the bed curtains.

f- After the radiographer has finished, the patient should return back to his position and made him as comfortable as possible.

g- The equipment should be put away with the tube column and tube head locked in a position, which prevent any dangers before it is taken from the ward.

h- We should separate the exposed film from the unexposed one.

Patient Special Conditions & Solution:

Patient with Oxygen Therapy: a The oxygen is supplied from cylinder or through a piped supply to the

patient’s bedside, and it is administered to him in one of three ways:1-By enclosing him in an oxygen tent.

2-By oxygen mask fitting over his mouth and nose.3-By tubes inserted up his nasal passages

b- There are two important points to remember when doing radiography on patients who are having oxygen:

1-The risk of fire and explosion. So in order to avoid this risk the oxygen supply should be switched off.

2-In case of very ill patient who is oxygen dependent, the patient and positions should be ready before the oxygen supply cut off, so that this is done for the shortest possible time and avoid any harm to the patient.

C- These should be done under the nurse supervision.

Patient with Intravenous Infusion:a- In some cases as part of the patient’s treatment it may be necessary to give him fluid or blood by a method other than oral administration. This is may be because of disability of the patient take any thing through his mouth or due to severe fluid loss.

b- The radiographer has no responsibility for altering or sitting the rate of flow of an intravenous infusion set, but while dealing with such a patient he should observe certain points:

1-If the needle become dislodge from its site in the vein and a swelling occur around the needle site this can indicate the needle is in the tissue then the in-charge nurse must be reported immediately.

2-If the infusion stops because of tubing kinked the radiographer should straight the tubing then call the in-charge nurse.

3-If the infusion stops then make sure that bandages and clothing on the limb are not tight, then call the in-charge nurse.

4-If the infusion stops because of the needle maybe against the vein wall, so the radiographer should straightening the limb then call the in-charge nurse.

5-If the infusion stops because of the head of the pressure is too law then the radiographer should raise the bottle, then call the in-charge nurse.

6-If the infusion stops because of blockage in the tube by a clot, this should be aspirated by a medical officer using sterile syringe.

c- During the X-ray equipment movement, the radiographer must notice the position of the infusion stand and avoid any strike

Patient with Tracheostomy:

A tracheostomy is a surgical opening in the upper trachea and a tube is passed, keeping the patient’s airway open and having an easy access to the patient trachea. This happened usually because of:

1-To overcome any obstruction in the upper airway route (e.g. mouth obstruction).

2-To allow secretions to be removed from the trachea and bronchi easily by suction tube (in patient who can’t cough effectively).

3-To improve effective ventilation of the lung.

4-To prevent the inhalation of the food, fluid and secretions by a patient whom has paralysis of the muscles involved in swallowing.

5-In unconscious, paralyzed and traumatic injury patient .

-These patients can’t speak, so communication skills technique should be concerned with this kind of patient (pencil and a writing pad should be provided).

-These patients need regular suction of the accumulate lungs secretions by the nurse in charge.

-The patient should be positioned in semi-erect of his back, to avoid any uncomfortable position.

-The radiographer should avoid any obstruction of the tube airway.

Patient with Nasogasteric Tube: -It is a tube passed through the nose and reaches the stomach, this tube used for

patient’s feeding. -The radiographer should avoid any dislodge or tension on the tube.

Patient with Drainage System: -It is a length of plastic tubing inserted into whichever cavity it is required to drain

and has a plastic bag at the end to measure the draining fluid (e.g. urine drainage system).

-The radiographer should avoid striking it or compressing or kinking the tube during moving the X-ray equipment or during the movement of the patient.

Patient with Traction: -It is used usually for fracture treatment (e.g. correct overriding bone fragment).

This can be achieved by applying weight. -The radiographer should avoid any releasing weight. He should be aware of the X-

ray equipment position. -The radiographer should avoid any movement of the effected limb.

Sterilization and Sterile -To sterilize anything for surgical purposes means to make it free from all

living organisms.

-Surgical procedures in hospital carry risk of infection for the patient.

-Methods of preventing infection are based upon the fact that the bacteria cannot effectively travel by themselves. Bacteria can be spread by a carrying media from one person to another in the following ways:

1-By direct contact: e.g. surgeon who has bacteria on his clothes or hands may transfer these organisms directly to his instruments, then to the patient via the operation wound. This can be prevented by not only use instruments and dressings which is have been made free from living organisms by sterilization, but also wear sterile gowns over his theatre cloths and sterile gloves on his hands. Anyone assisting the surgeon should follow the same precaution.

2-By aerial carriage: dust or droplet may carry infection (bacteria) through the air. The most important but not obvious aerial way is by droplet infection. This happened when the bacteria transferred into an operation wound by fine particles of moisture carried by the surgeon breath from his nose and mouth. These bacteria haven’t harms to the carrier (carriers fell well) but could be harmful to others. This can be prevented by wearing a mask which covers both mouth and nose and is designed to act as a barrier.

3-By Food and Water carriage: food and water are often vehicles for the transport of bacteria. This can be done by contamination of the food and the water by dirty hands or by exposing food to air for long time. This can be prevented by hands washing of the people who handle food, they should wear gloves also, and wrapping of foods also has a major rule to exclude infection.

4-By insect carriage. -During surgery direct contact and aerial spread by droplet infection are the most

likely ways for bacteria to be carried to the patient. -Any small mistake should be avoiding, and if it does occur it should not be ignored

or passed over.

4-By insect carriage:.

-During surgery direct contact and aerial spread by droplet infection are the most likely ways for bacteria to be carried to the patient.

-Any small mistake should be avoiding, and if it does occur it should not be ignored or passed over.

-Bacteria are microscopic organisms, which live, reproduce, and die. In order to live they require the following:A-Food-protein, carbohydrate, and mineral salts taken from tissue cells.B-Moisture.C-Oxygen.D-Suitable temperature (37°-38°C).E-Suitable PH.

-Aseptic technique could be achieved by disturbing one or more of the above conditions; this could kill or stop the growth of these organisms.

Methods of Sterilization:•Sterilization by Heat:

-Since heat kills all form of bacteria it is the method of choice, unless it cannot be used because it will prove damaging to the material which is to be sterilized.

-In order to kill all kinds of bacteria (resistible bacteria) it is necessary to achieve higher temperatures and longer periods of exposure than other

kinds .

-Heat can be applied to sterilization in the following ways:

Sterilization by Boiling.

Sterilization by Steam under pressure.

Sterilization by Dry Heat.

Sterilization by Boiling:- Boiling in plain water has traditionally used as a means of sterilization.- Boiling for 2 minutes destroys organisms, but the usual practice is to extend the boiling time to 5 minutes to give added safety.- Before boiling the articles for sterilization, they should be washed by soap to remove any barium, mucus, pus, blood etc, with which they may be stained.- The water level in the sterilizer must be high enough to cover all the articles which are in it.- The period of 5 minutes should be timed only after the water has come to a ‘full rolling boil’.- It must be remembered that once they have been sterilized, articles must be handled with sterile forceps and must not be allowed to make contact with unsteriled surfaces.

Sterilization by Steam under Pressure: -Sterilization by steam under pressure is the most efficient procedure. It carried

out in apiece of equipment called an autoclave. Articles put in autoclave are subjected to the action of steam at pressures above atmospheric pressure and temperatures above the boiling point of water.

-In hospital, large autoclaves are found in sterilization department. In order to make use of such autoclaves, the articles which are to be sterilized must be packed into a suitable container. This container usually made of nylon film and special paper bag which has perforations at its side, these perforations open during high pressure and heat and allow the steam to fully penetrate the interior. and they are then closed under normal heat condition.

-The modern autoclave equipment is very effective. It is a high-pressure & high vacuum equipment reaches higher temperatures more quickly, and sterilization is achieved in very much shorter times than would be possible in the past.

-There are two methods to check the efficiency of an autoclaving process, the first one is by placing special tape on the surface of each container before the process and check the color of this after the process (dark color means effective sterilization took place), the second method is done from time to time which called the bacteriological tests. This test can be done by placing a small glass tube into on of the container; this tube has a bacteria in it which can be tested after the process to determine the efficiency of this process.

Sterilization by Dry Heat:

- Moist heat is more penetrating and effective than dry heat, but hot dry air (or alternatively infra-red rays) can be used for efficient sterilization in an oven. This method is suitable for fragile glass ware such as test-tubes and syringes.

Sterilization by Gamma Radiation:

- Gamma radiation, like heat, is a physical method of sterilization. Exposure to these electromagnetic radiations of very short wavelength is lethal todisease-producing organisms. It has the advantage that the penetration character of the radiation enables it to be used to sterilize articles after they have been packaged. It may be used to sterilize articles which cannot be exposed to heat.

Sterilization by Chemical Disinfection:-Chemical disinfectants and antiseptics have certain limitations in use. This method

is less effective than any other sterilization method by heat. An efficient way of achieving complete sterility is to expose the organisms to a great enough heat for a long enough time, but obviously this is not possible with all materials and all equipment at all time.

-This chemical sterilization has two actions to the bacteria:Kill bacteria (bactericidal agent):

If we want to kill bacteria in the articles we must put these articles in greater strength chemical agent-like formalin for a long time. This method is used to store instruments which had been previously sterilized by heat.Inhibit the growth of bacteria (bacteriostatic agent):

If we want to inhibit the growth of the bacteria, we should put the articles in the chemical agent with great strength for less time, usually 20 minutes.

-This method usually used if heat could not be employed, although there is no method of chemical sterilization which is completely effective in the sense that it will

kill all organisms .-Some special concerns should be aware during the process of using this method:

1 .All articles must be cleaned with soap and water before putting it in the agent. This to remove any mucus, pus, blood, etc.

2.The container holding the disinfectant solutions must be itself sterilized before putting the solution agent.

3.The solution agent must be totally covered the articles.

Central Sterilization Supply Department: -Establishing this department in a hospital is very essential and has great

advantages. This department supplies all departments of the hospital by daily and ready sterilized equipment. This removes from the wards and special departments such as the X-ray department the need to operate their own sterilizing system. The nurse and worker are freed from the tasks of sterilization, which will give them the chase to spend their time in direct care of patient.

-In order to use the central supply department, the ward or department in the hospital send its daily requirements of sterilized equipments needed then they will receive this inn suitable packs-such as nylon film, and metal cylinders (for syringes)-these equipment being returned to the central supply department after use.

-The modern tendency is towards making disposable equipments as much as they can; this means these equipments will be used once and then discarded. The material which they usually use to produce disposable equipment is Aluminum foil, and plastic. Aluminum foil bowls, trays, syringes, forceps, urinals, needles, and paper dressing towels are all examples of disposable equipments used recently. Using this kind of equipment is important to save time and labor and an increase in patient’s safety.

Note: it is important to stressed that continuous care is necessary in the handling of sterile

equipment .The radiographer should avoid any direct contact with the sterilized equipment by his hands; the radiographer should handle it by sterilized forceps or by wearing gloves even if his hands have been cleaned by soap, all equipment must be kept sterilized. If any contamination occurs, even the slightest, to the equipment must not be then be used, it must be destabilized at whatever cost in time and effort may be necessary.

Tomography-Conventional radiography is a two-dimensional image of all the structures

between the x-ray tube and the film. This result in the superimposition of the images derived from structures at all levels of the body in the path of the x-ray beam. The image of the structure in one layer of the body can be obscured by superimposition on it of images of structures in layers above and below it.

-Tomography is a technique whereby images of the structures in any selected layers are recorded sharply while images of structures outside the selected layer are blurred.

-The general principle method of tomography is throughout the exposure

movement occurs causing images from the unwanted layers to move relative to the film and are therefore unsharp, while images from the selected layer are kept stationary relative to the film and are recorded

sharply .-Tomography involves the synchronized movement of any two of the three

elements, the x-ray tube, the film and patient, while the third element remains stationary. If there is movement of the patient only during the

exposure this is called autotomography.

Autotomography mandible moving during exposure.

Tomography X-ray tube & film move during exposure.

With Arrested Respiration.

With Gentle Respiration.

Principles of Tomography:

-A tomographic image can be produced by the patient remains stationary while the X-ray tube and film move. This is the most common method used .

-For all tomographic method, the two moving elements are linked so that they move in coordination .

As the X-ray tube moves over the patient, the projected images of structures on different levels of the body will move with different velocities; the near the structure is to the X-ray tube the faster its image will move.

Due to the linked movement of the X-ray tube and film, the film moves at the same velocity as images of structures only at the level of the pivot therefore only these images are recorded on the same part of the film throughout the movement.

Images of structures on all other layers move at a different velocity to that of the film and are not recorded on the same part of the film throughout the movement and are therefore blurred.

It is therefore possible to record sharp images of structures on one layer of the body only, free from obscuring images from other layers .

-The x-ray tube is connected to the cassette and pivoted at B. -When the x-ray tube moves from T1 to T2 during the exposure,

Images of layer B move at the same velocity as the film and are recorded on the same part of the film throughout the exposure.

-The images are sharp.-Images of layer A move faster than the film and are therefore

blurred. -Images of layer C moves slower than the film and are therefore

blurred.

Depth of Layer: -The height of the pivot above the table top is variable so that any level in the

patient can be selected for tomography. This pivot can be raised or lowered above the table top to the required level in the patient body (variable pivot). The height of the pivot above the table is indicated on scale.

Types of Tomographic movement: Basically there are two categories of tomographic movement:

1.linear movement. 2 .Multidirectional movement:

a-Circular M.b-Elliptical M.c-Spiral M.d-Figure of eight M.

e-Hypocycloidal M The Linear m. is the simple, easy to obtain and satisfactory for many kinds of

examinations.

Line-to-Line Movement: it is the simplest form of tomographic movement, which includes line to line. The X-

ray tube and film move in lines parallel to the table top. The FFD changes throughout the movement, being smallest at the midpoint of the movement. Line to line movement is often confined to one direction only.

Arc-to-Arc Movement: The X-ray tube and film move in arcs, the center of the rotation being the pivot.

Throughout the movement the film remains parallel to the table top and the focus-to-film (FFD) distance is constant. The advantage of this kind of movement is the complete effect of blurring out of the superimposed images, which the linear movement has less blurring effect.

Exposure Angle: The exposure angle is the angle which the tube moves during the exposure. For

linear, circular, and elliptical movements there is usually a choice of exposure angle ranging from about 2 to 40 degrees but for spiral, figure of eight or hypocycloidal movements the exposure angle is usually greater than 30 degrees. These large angles are associated with long exposure times, i.e. not less than about 3 seconds and this is a factor to be taken into consideration when choosing the type of movement to use.

Thickness of Layer: Only images of structures at the level of the pivot and parallel to the film are

recorded on the same part of the film throughout the movement (look figure A). If the exposure angle is small (e.g. less than 0.6 mm) the images of structures outside this object plane move relative to the film, but these images will be recognizable images, because of the thick layer that has been recorded.

The amount of relative movement of the image and therefore the thickness of the layer depends on the exposure angle. The greater the exposure angle the thinner the layer.

Layer of thickness also depends on the distance of the structure above or below the pivot. Images of structures above the pivot are blurred more than those below the pivot, i.e. the structures close to the object plane can be more easily ‘blurred out’ if they are on the tube side of the patient, thus the layer is thinner above the pivot than the below (look figure B).

-The following graph shows how the thickness of the layer varies with exposure angle. At the larger angles there is little change in layer thickness with change in exposure angle. But at the smaller angles small change in exposure angle causes a large change in layer thickness.

Simultaneous Multi-Sectional Tomography: -In this technique, several layers of the body can be recorded using one

tomographic exposure. A film situated at the level of the lower attachment of the connecting rod will record sharp images of structures at the level of the pivot, but in addition, films placed at lower levels will record sharp images of structures on layers

lower than the pivot (Fig 1) . -Advantages of this technique are that:

It reduces radiation dose to the patient.It reduces examination time.

Capability to take many radiographs in the same position and in the same phase of respiration.They are more comparable than films taken with sequential exposures.

-Intensifying screens: to compensate for the attenuation of the X-ray beam by the successive screens and

by the reduction in intensity due to the inverse square law, the screens have an increase in speed from above downwards, i.e. a graduated change from the slowest screens nearest the X-ray tube to the fastest screens furthest away from the tube. With the correct choice of screens, all films will be comparable in terms of density. Each pair of intensifying screen carries a number which appears on the radiograph so that after processing the films can be placed in their correct order and marked with their correct layer height.

Image Quality: Generally the quality of a tomographic image, in terms of its sharpness and

contrast, is not as good as that of a standard radiographic image. Contrast: As the layer being thinner the contrast being more lower, because

thinner layers need more blurring effect to take place to get rid of the large superimposition area around the interested object, i.e. contrast is further reduced by the superimposition on the tomographic image of the blurred images of structures outside the chosen layer. To improve contrast, particular attention should be paid to the control of scattered radiation by collimating the X-ray beam to the smallest possible field and also by reducing the kV factor which will still give effective penetration.

Sharpness: As with a standard radiographic image, unsharpness can be due to patient movement, focal spot size and intensifying screens, but in addition the tomographic movement and long pivot-to-film distance can introduce a source of image unsharpness. Because tomographic movement has an affect on the image sharpness we should be aware of the following; tomographic exposure can be long (up to 6 seconds) therefore immobilization of the patient in a comfortable position is essential, where involuntary movement can occur, a short exposure time is necessary, we should also avoid any vibrational movement of the X-ray tube or the film.

Practical Considerations:

Localization of the depth of the layer required:Often the approximate depth is known from past experience or from record kept of similar examinations, or by measuring the depth especially for superficial structures.

Radiation Protection: We can reduce the radiation dose to the patient by applying the following:

The position and depth of the interested object should be accurately localized to avoid any repeated exposure.

The position of the interested object should be as parallel as you can to reduce the number of layers needed for a complete record of the structure.

In skull tomography when the radiation is directed towards the patient’s eyes we should protect the patient lens by position him on prone position or by placing lead sheet on the eyes.Good collimation is good for radiation protection and image quality .

Tomographic procedure:Good understanding of the patient request and selecting the tomographic movement required before starting are very important.

Previous films are important if available for easy object localization (to know the extent and the depth of the structure).

Knowing the exposure time and the patient condition are important to avoid any repeated radiograph.The exposure factors are set, with the required exposure time.

After the patient has been explained the procedure, the patient should be positioned on the table an immobilized.Center and collimate the X-ray beam to the interested region.The exposure angle and the pivot are set.The cassette is being placed on the tray.The patient is given the last instructions before the exposure is made.

After processing the film the radiographer should check the positioning, exposure, contrast and localization to determine if any further radiographs are needed.

If initial localization of the depth of the layer is uncertain, it might be advisable to take first a thick layer (small exposure angle) or to use multi-sectional cassette to

locate the structure .