X-RAYS

PRODUCTION AND PROPERTIES OF X – RAYS

BASIC INTERACTION OF X-RAY WITH MATTER

• For an x-ray examination, the part to be examined is kept between the x-ray source and an x-ray film. Thus the x-ray beam emitted by the machine traverse through the part to be examined to reach the film, carrying useful information that is recorded as a image on the film. While passing through the patient.
• Some x-rays are differentially transmitted through the patient carrying information. Some photons are absorbed and least to exist.
• X ray photon can interact with matter in five ways of which the Photoelectric effect and Compton effect are important in diagnostic radiology.
  Photoelectric effect

• The effect is mostly produced when x-ray photos interact with inner shell electrons of a atom (KLM).
  Compton effect

• As an incident photon encountered a free electron of the outer shall of the atom, the photon travel in a new direction as scatter radiation.
• When an incident photon with energy slightly greater than the binding energy of a k shell electron encounter the scatter, the k shell electron is affected from its shell.
• The free electron flies off as photoelectron. Another electron from an adjacent or outer shell of another atom immediately fills in to the void created by an ejected electron. As this electron drops in to the created void, it gives off energy is the form of characteristic radiation.

TYPES OF X-RAY APPARATUS

Portable apparatus (70 - 90 Kv and 15-30 mA.)

• The advantages are
  • They are less in cost, and portable
  • They need little maintanence.
  • They can be operated from any 15 A electrical point .
• The disadvantages is

•  longer exposure time
•  predisposes to movement blur.
• Uses
• Suitable for x-raying of limbs
• For  small animals.

Mobile x-ray apparatus (125 kv and 300mA)

• They are mounted on wheels , and are cumbersome to use for restive animals.
• Uses
• Can be used for large animal and  for small animal practices

Fixed x-ray apparatus (120-200kv  and 300 - 1000mA )

• This machine requires transformer which have to be built in the room and special electric connection (3 phase).
•  This type of machines are suitable only for big institutions
• Highly  expensive .
•  Suitable for both large animal and small animal radiography.
  Properties of x-ray beam

• Invisible to eye
• Cannot be felt
• No Charge/Mass
• Not deflected by magnetic field
• Travel at speed of light
• Travel in  straight line
• They can penetrate objects of different  densities  and thickness
• Photographic effect - x-rays ionises photographic emulsions of silver halide  crystals on  film
• Fluorescent effect - zinc sulphide, calcium tungstate etc fluoresce when exposed to x-rays & emit green or blue light.
• Biological effect - x-rays ionises the atoms ,  causes Mutation of DNA, Cancers, Cataracts
  Collimation of X-ray beam

• To collimate or restrict the beam of X-rays as it releases  divergent rays.
• The purpose is
  • To prevent unnecessary radiations  
  • To reduce the scattered radiations.
• This is done by using cones or light beam diaphragms.

PARTS OF X-RAY MACHINE

• It consists of four main parts
• X-ray tube,
• Transformers,
• Tube stand and
• Control panel.

X-ray tube

• An X-ray tube consists of a large thermionic diode glass tube which has been evacuated to produce a high vacuum and in to which are sealed two electrodes, the cathode (-) and the anode (+).

•  The cathode (-) and the anode (+)  are placed 1 - 3 cm apart.
• The glass tube is made of borosilicate to with stand high temperature.
• The passage of a high kilo voltage electric current across the electrodes results in the production of X-rays.
• The glass tube is fitted in to an oil filled casing and the whole assembly is housed in a metal encased with lead covering with a small opening for the useful X-rays to exit after filtration.
• The vacuum in the tube creates a free flow for the electron beam and also prevents oxidation of cathode filament.
•   The oil in the tube helps to dissipate heat apart from acting as a electrical insulator.
• Cathode

• The negative electrode consists of tungsten filament with high melting point ( 3370 c) and a focussing cup(Ni/Mo) and it serves as the source of electrons.
• The tube current is measured in milli amperages and decides the number of electrons flowing per second from the filament to the target.
• Immediately prior to making an x ray exposure the filament is heated to create an electron cloud by a low voltage current.
• The tube current decides the quantity or intensity of the x rays produced.

• Anode
  • Anode is the target made up of thin sheet of tungsten embedded in a copper block, which obstructs the electrons and energy  is produced. The  99 % of it is converted in to heat, the heat produced at the target is rapidly transferred to the copper block and hence to the oil. The anode angle differs according to individual tube design and may vary between 10 deg and 20 deg and the size of the focal spot may vary from 0.3mm to 2 mm.
  • The x ray beam should arise from the smallest practical portion of the anode, termed as target or focal spot.
  • There are two types of anode - stationary and rotating.
    Transformers

• A auto transformer corrects the fluctuations in input voltage, step down transformer reduces voltage to the cathode, and the step up transformer produces a high voltage current for the production of x rays.
  Tube stand

• This is to support the x ray tube during the exposure.

Control panel

• This contains the  on and off switches , kilovoltage selector, milli amperage selector, the timer and exposure button.

PRODUCTION OF X-RAYS

• X rays are produced by energy conversion when a fast moving streams of electrons is suddenly hit  the target anode, electrons in K orbit are ejected and electrons in higher orbits give up some energy as characteristic  X-rays and fill the gap in K orbit.
• Most of the energy (over 99%) will be transformed into heat; the reminder of the energy will be converted into x-rays.
• As x-ray beam passes through the patient differential absorption takes place depending on the tissue density and shadowgraph is obtained.

• X rays are generated by two different process when high speed electrons lose energy in the target of the x ray tube due to radioactive  interaction.
  Characteristic radiation or Line radiation

• When the projectile electron interacts with the electron in the K shell of the target  atom, it results in the ejection of electron in the K shell if the energy of the projectile electron exceeds the binding energy of the ejected electron. This results in transient electron vacancy in the K shell into which an electron from the outer shell falls and this process continues till the atom becomes stable. This shifting of electrons results in emission of X-ray photon which possesses  an energy equal to the difference between the binding energies of the electrons involved. Hence the X-ray photon energy is characteristic  of the shells involved in an element and so called as characteristic radiation.
  Bremstrahlung radiation or Breaking radiation

• When the projectile electron approaches the nucleus of the atom avoiding the orbital electrons, it slows down, due to the opposite charges, and gets deflected  from its original course. During this the incident electron loses its kinetic energy, due to its slow down, and this loss of kinetic energy is emitted as X-ray photon.

• The X-ray produced by this type is called bremstrahlung or breaking radiation. The incident electron may also collide with the nucleus at times, converting all its kinetic energy to a single X-ray photon. 

FACTORS INFLUENCING PRODUCTION OF X- RAYS

FACTORS AFFECTING RADIOGRAPHIC QUALITY

• An good diagnostic radiograph is one is which there excellent details, correct density and the proper scale of contrast. The proper use of various radiographic exposure factors KVP, mA, Time and FFD are employed.
  Qualities of a radiograph are determined by Density, Contrast, Sharpness and Detail
  Density

•  It is a measure of the degree of blackness of the film.
• Radiographic density is affected by the subject density
•  Higher milli amperage produces more x-rays and thus more density and lower milli amperage results is less density.
•  Radiographic density varies directly with exposure time.
  Contrast

•     Radiographic contrast is the difference in density between the image of parts or structures on the radiograph.
•     Contrast is the difference between blacks, grays and whites.  
•     Radiographic contrast varies inversely with the kilovoltage.  
•     Secondary radiation and scattered radiations causes lack of contrast.
•     Improper development of film and use of warm developer cause lack of contrast.
•     To get good radiograph the following technique should be followed
  • Fastest exposure time possible (To prevent movement blur)
  • Higher kvp.
  • Constant distance
  • Constant milliamperage
  • Relative transparency of the of various structures
  • Type or speed of film
  • Intensifying screens
    Sharpness (Definition)
    The sharpness is indicated by the well defined demarcations between various structures that are recorded.
    Detail

• Detail is the degree of definitions of an object on a radiograph. The factors affecting the detail are:

• Shorter Focal , film distance. (FFD)
• Closeness of the object to the film.
• Use of intensifying screen.
• Movement of either the patient.
• Over exposure or under exposure.
• Focal spot size.

Viewing of the radiograph

• Radiograph should be viewed on a good, evenly lit viewing box, in a semi darkened room.
• When viewing radiographs of the dorsoventral or ventrodorsal or skull, the left side of the film should be facing the viewers right side and when viewing the lateral views it would be better that the anterior aspect should be directed towards the left side of the viewers.
•  To give radiological interpretation the viewer must have a comprehensive data of clinical and physical examinations and also have a knowledge of the range of radiological animal anatomy and for this a library of normal films taken in the standard position is an asset.

PRINCIPLES OF VIEWING AND INTERPRETING X - RAY FILMS

HANDLING, VIEWING AND INTERPRETATION OF X-RAYS

Handling

• Cassettes with exposed film should be opened in a dark room and the film is removed by holding the corners. The film is loaded in a suitable size cassette and stored in lead lined boxes.
• The loaded cassettes and the exposed film cassettes are kept with radio opaque surface upwards. Unexposed film boxes are always kept in lead lined boxes.
  Viewing

• Radiography should be viewed on a good evenly lit viewing box in a semi darkened room.
• Dorsoventral chest, ventrodorsal abdomen or skulls are viewed with a right side of the film facing the viewer’s left side.
• Lateral view radiographs are viewed by placing it facing left. Radiographs of extremities are viewed with lateral aspect on left side of the viewer.
  Interpretation

• The three important factors to be considered before interpreting a radiograph are
  • Case history,
  • Physical examination and
  • Correct radiographic technique.
    Radiographic diagnosis

• Radiographic diagnosis consists of two parts namely location of the lesion and classification of the lesion.
• Location of the lesion requires knowledge of normal radiographic anatomy, basic radiographic signs in terms of changes such as size, architecture, contour, density, position and function.  
  Classification of Lesion

• The lesions in the radiograph are classified as developmental, metabolic, traumatic, infectious, neoplastic, and degenerative.

RADIOLOGICAL PATHOLOGY OF THORAX  Cardiomegaly Outline of the heart becomes more rounded. Occupies a much larger area of the thorax. Trachea and major blood vessels are seen displaced. Posterior border of heart becomes straighter. Cardiac silhouette in contact with sternum and diaphragm. Bronchitis Slight increase in the radio-density of the bronchial tree Pneumonia Areas of increased density of lung substance. Areas of consolidation can be visualized Pneumothorax Collapse of the lungs. Presence of air in the pleural cavity Floating heart shadow Fluid in the pleural cavity Fluid shadow will be masking the structures in the thorax. Fluid level appears as area of increased density. Typical leafy appearance Diaphragmatic Hernia Disappearance of the normal diaphragm line. Displacement of lungs and visualization of part of GI tract in thoracic cavity. Tuberculosis Areas of opacity in lung parenchyma Recognition of cavitations and calcified nodules in the lung parenchyma or pleura.
RADIOLOGICAL PATHOLOGY  OF                      ABDOMEN

Gastric torsion

• Greatly distended gas filled organ occupying the major portion of the anterior abdomen. Compartmentalization of stomach.

Oesophageal foreign body

• Thickening of the oesophageal wall
• Increased density from that of the surrounding tissues.

Pyloric Obstruction

• Enlargement of the stomach
• Accumulation of fluids/material (accumulation of barium) in pyloric area.

Intussusceptions

• Sausage shaped mass with increased density
• Thin layer of gas outlining the layers of intussusceptions
• Barium enema- ‘coiled watch spring’ pattern.

Hydronephrosis

• Large mass with a smooth outline in the anterior abdomen filled with fluids, with appearance of homogenous density

Kidney calculi

• Small irregular dense areas roughly central to the kidney outline

Cystic calculi

• Radio opaque cystic calculi easily visualized slightly radio opaque calculi can be demonstrated by using penumo cystography.

Prostate enlargement

• Relatively dense mass just anterior and ventral to the pelvic brim in the position normally occupied by the bladder, which is displaced anteriorly.

Metritis and pyometra

• Slight thickening and enlargement of uterus- may be uniformly tubular or sacculated.
• Displacement of the colon.

RADIOGRAPHIC LESIONS - LIMBS

RADIOLOGICAL PATHOLGY OF BONES AND JOINTS

Radiographic signs of bone diseases

• Altered contour of the bone
• Altered size of the bone
• Decreased one density
• Change in trabecular pattern

Radiographic signs of joint diseases

• Widening or narrowing of the joint space
• Cystic changes
• Swollen joint capsule-soft tissue swelling

Osteoporosis

• Diminished density of the bone.

Small animals

• Hip dysplasia

• Bony exostosis, new bone formation involving acetabulum- thickened disorganized appearance of the femoral neck-remodeling and flattening of the femoral head.

• Hip dislocation
• Abnormal width of intra articular space.
• Long bone fractures
• Disruption of the continuity of a bone

CONTRAST RADIOGRAPHY - CLASSIFICATION, MATERIALS, INDICATIONS AND CONTRA INDICATION

CONTRAST RADIOGRAPHY - CLASSIFICATIONS

• Radiography is founded upon the principle that an object when exposed to an incident x-ray beam will absorb a part of the x-ray beam and a part will penetrate the object and interact with the film.
•  Radio dense objects absorb larger percentage of the x-rays than radiolucent objects resulting in less film exposure.
• In other words, the absorption of x-ray by the tissues of the body, and thus their radio density, depends upon the atomic weight of the principal substances of which the tissues are composed.  
  Density of various objects

• Barium - 56
• Bone - 14  
• Muscle, Organ, fluid
• Soft tissue 7.4  
• Fat - 6.3
• Gas (Air) - 1 to 2

• The differences in density (radiographic contrast) between bones, muscles, fat and gas form the basis of plain film radiography.  
•  Artificial methods of delineating such organs are required and so a suitable contrast medium is employed. The contrast medium may have either high atomic weight and provide positive contrast or a low atomic weight and provide negative contrast. Examples of positive contrast media re Barium sulphate, organic iodine compounds. Examples of negative contrast media area co2, o2 and N20 or atmospheric air.

•  The ideal criteria for the contrast media include
•  (1) Opaque to x-rays
•  (2) Pharmacologically inert
• (3) Very water soluble so that they can be injected at high concentrations
•  (4) Chemically stable
•  (5) Rapidly excreted by the kidneys
• (6) Low viscosity
•  (7) Low toxicity and irritancy.
   Ex: Conray, Urografin (Ionic agent);
            Iohexol, Iopamidol metrizamide (non-ionic)
            Agents excreated selectively through biliary system to study the gall    
            bladder, after absorption from alimentary system or intravascular    
            injection. Ex: Biligrafin.   
   

INTRAVASCULAR CONTRAST AGENTS AND CONTRAST RADIOGRAPY

 

CONVENTIONAL IONIC MEDIA
Generic name	Proprietary name
Meglumine iothalamate	Conray-280
Sodium diatrizoate	Urografin-370
NEW LOW OSMOLAR NON-IONIC MEDIA
Metrizamide	Amipaque
Iopamidol	Niopam
Iohexol	Omnipaque

Angiography

• The radiographic demonstration of the vascular system by the injection of a water soluble organic iodide compound into a suitable vessel. Specialized techniques
  • Arteriography-Arteries
  • Venography-Veins
  • Aortography-aorta
  • Portal venography–Portal vein

• Angiocardiography-Heart and vessels
• Cerebral angiography–Cerebral vessels

RADIOGRAPHY OF ALIMENTARY TRACT

Indications

• To reveal obstruction of the alimentary tract. Ex: Tumour or stenosis.
• To find out distorsion of the wall of alimentary tract such as enlargement. Ex: Dilatation of stomach or oesophagus.
• To find out displacement of the alimentary tract. Ex: Hernia.
• To reveal lesions in the wall of the alimentary tract. Ex: Neoplasms – Ulcer.
  Procedure

• No preparation is required. Take plain radiography and administer Barium sulphate paste about 50 to 100 Gms. Orally (Braium Swallow) and taken with lateral and ventrodorsal projections immediately after administration.
   

CONTRAST RADIOGRAPHY - URINARY SYSTEM AND SPINAL CORD

MYELOGRAPHY

Indication

• To outline the neural canal
• To demonstrate disc lesions and other space occupying lesions.
• Contrast agents used
• Oily fluid containing 40% iodine (Ex. Myodil).
• Water soluble: Metrizamide soluble. Iohexol, Iopamidol solution.

• Under general anaesthesia the contrast agent is injected into the sub-arachnoid space.

UROGRAPHY: (PYELOGRAPHY AND CYSTOGRAPHY)

Intravenous urography (Intravenous pyelography, IVP)

• Pyelography is used to demonstrate kidney shadow when it cannot be demonstrated in a straight radiography.
•  To get a rough indications about renal function.
• Contrast agents used

• Ionic contrast agents such as sodium Iothalamate (conray-420); Meglumine Iothelamate (conray-280);  Metrizamide have also been used.
• Dosage: To give better demonstration upto 600 mg to 1200 mg/kg. Body weight may be administered I/V usually 1 to 2 ml/kg. Body weight.
• Preparation: With hold food for 24 hrs. and water for 12 hrs. Empty the bowels with enemata.   
  Cystography

• Indications

1.      To recogrise radiolucent small calculi

2.      To demonstrate space occupying lesions in the bladder.

3.      To demonstrate abnormal prostate gland.

• Preparation: The G.I. tract should be empty. Iodine compund 10 to 20% about 40 to 100 ml. Are employed after catheterizing the bladder.