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Radiation is defined as  a type of energy that comes from a source and travels through material or some space.
It is broadly categorized into two types:
  1. Ionizing Radiation: Ionizing radiation is radiation that can produce charged particles (ions) in materials that it strikes. The ionization resulting from protons, electrons, and gamma rays is either a direct or indirect (i.e., mediated through water) effect of particles or photons on DNA. 
  2. Non Ionizing radiation: Non-ionizing radiation refers to any type of electromagnetic radiation that does not carry enough energy per quantum to ionize atoms or molecules—that is, to completely remove an electron from an atom or molecule. 
Radiation can also be: –
  1. Particulate radiation
    1. Alpha particles
    2. Beta particles
  2. Electromagnetic Radiation
    1. Radio waves
    2. Microwaves
    3. Infrared waves
    4. Ultraviolet light
    5. Gamma radiation
    6. X - radiation
 Major Sources of ionizing radiation include
  1. Most nuclear processes (e.g., nuclear fission, nuclear fusion, radioactive decay),
  2. X-ray equipment,
  3. high-energy physics experiments, and
  4. Background radiation.
Type Mass Charge Comment
1). X-ray
2). Gamma ray
1). Electron (e)
2). Proton (p)
3). Neutron (n)
4). Alpha particle
9.1 X 10-31kg 2000 X e
2000 X e
2p+2n =8000 X e
X-rays and gamma rays do not differ except in the source.
Gamma rays are produced intranuclearly, and x-rays are produced extranuclearly (i.e., mechanically).

Exhibits a Bragg peak
Cannot be accelerated by an electrical field
Helium nucleus


  1. Wilhelm Conrad Roentgen, a German physicist, discovered X-rays on November 8, 1895.
  2. By 28th December 1895, he investigated properties of the rays and was awarded the first Nobel Prize for Physics in 1901.
Parts of X ray tube

  1. X-rays are produced whenever a stream of fast-moving electrons undergo rapid deceleration and these conditions prevail during operation of special thermionic vacuum tube called as hot filament or Coolidge X-ray tube.
  2. A typical X-ray tube is a thermionic diode consisting of a tungsten filament cathode, a tungsten target anode, an evacuated glass tube enclosure (Pyrex glass) and 2 circuits to heat the filament and to drive the space charge electrons to anode.
    in Mammography, the target is made up of molybdenum
    1. the electron beam is generated at cathode by heating the cathode, which releases electron by the process of thermoionic emission
    2. Intensity is proportional to (kVp)2.
    3. The quantity of X-rays produced depends on atomic number of target material, kVp and mA, while the quality depends on kVp only.
  1. Two basic mechanisms by which x-rays are produced at anode
    1. Continuous spectrum / Bremmstrahlung : Interaction of electron with nucleus.
      The accelerated electron on reaching the anode comes very close to a nucleus of tungsten, is deviated due to opposite charge of the nucleus. This deviation not just changes its direction, but leads to loss of some of its energy, which is emitted as a X-ray photon. Because the prior electron energy, its distance from nucleus, resultant deviation produced are all variable factors the Xrays emitted have variable energies. These energies when plotted give a continuous spectrum, hence the name.
    2. Characteristic spectrum :  Interaction of electron with inner shell electron.
      The electron beam strikes the inner shell electron of tungsten, such that it is thrown out of orbit. An electron void is created which makes the tungsten atom unstable. This void is filled by a oter shell electron jumping to the inner orbit. In doing so this jumping electron needs to lose some energy to reach the low energy level of inner orbit. This energy lost is emitted as X-rays. Because the difference in energy levels of orbits is fixed the Xray emitted have a discrete constant energy value hence the name. 

Increasing voltage (kV) decreases contrast and increases penetration. Increasing milliampere-seconds (mAs) increases contrast by increasing the background blackening.

  1. X-ray filters are sheets of metal (aluminum filters are commonly used) placed in the path of x-ray beam near the x-ray tube housing to absorb low energy radiation before it reaches the patient. They are simple and inexpensive. Their main function is to protect the patient from useless (low energy) radiation. They reduce skin exposures by as much as 80%. NCRP recommends an equivalent of 2.5 mm of aluminum permanent filtration for diagnostic x-ray beams of energy more than 70 kvp.
  2. Collimators: beam restricting device, restricts the path of X ray beam and reduces scatter radiation.
  3. Grids: Parallel lead lines, which absorbs scatter radiation and improves image quality.
  4. Intensifying Screens: these are made up of calcium tungstate or rare earth metals. these screens converts X-rays to light photon, as films are more sensitive to light and less exposure is required.
  1. The five basic ways that an x-ray photon can interact with atom/matter are:
    1. Photoelectric effectQ                                           
    2. Coherent scattering                     
    3. Compton scattering
    4. Pair production                                                     
    5. Photodisintegration
  1. Photoelectric interaction
  1. It predominates in diagnostic radiology.
  2. It predominates at lower energy.
  3. The innermost shell of an atom is called K shell, and the more peripheral shells are named consecutively L, M, N, and so forth. Q
  4. When an incident photon, with little more energy than the binding energy of K-shell electron, encounters one of these electrons, it ejects it from orbit and the photon disappears, giving up all its energy to electron. This electron now flies into space and is absorbed. Thus the atom is now left with an electron void on the K shell, which is filled up soon by as a electron from adjacent shell drops into K shell, giving up energy in the form of X-ray photon. This is photoelectric effect.
  5. This is similar to the production of characteristic spectrum radiation. But the difference is the target atom involved. In X-ray tube it is tungsten with large difference in its shell energy levels hence, emerging Xray beam has a significant amount of energy. In contrast when this occurs in body tissues the atoms involved are H, O, C with very low atomic numbers compared to tungsten. The difference in shell energies is also very low, hence the emerging beam has very little energy. It is immediately attenuated and is insignificant as such.
Extra Edge

Structures in the body that are very dense (such as those that contain calcium) attenuate a large amount of the x-ray beam; thus the x-ray beam is not able to reach the film and darken it, and such structures appear white on a radiograph. Conversely, structures that are not very dense (such as air) allow the x-ray beam to penetrate and darken the film; thus such structures appear black

  1. Compton Scattering : 
  1. It is the most common interaction occurring and leads to production of scatter radiation.
  2. It is interaction of Xray photon with outer shell electron. The Xray photon knocks off the outer shell electron, loses only a small part of its energy and is deviated.
  3. This deviation, if by small angles may reach the film and thus becomes scatter radiation adding noise to the film.
  1. X-RAY Films used in medical imaging
    1. Double emulsion/coated(duplitized) films Q: have emulsion, applied to both sides of the plastic base in order to increase sensitivity.
      1. General purpose conventional radiography films
      2. Intra-oral dental films
      3. Kidney surgery films
      4. Radiation monitoring films
    2. Single emulsion/coated films: have emulsion applied only to one side of its base. Their main advantage is high quality images..E.g. 
      1. Photofluorographic film
      2. Cathode-ray tube (CRT) photography                                                             
      3. Duplication film
      4. Subtraction film                                                                                                   
      5. Laser imaging film
      6. Mammography film                                                                                            
      7. Computed tomography (CT) film
      8. Radionuclide imaging film                                                                 
      9. Diagnostic ultrasound film
      10. Computed radiography (CR system) film
Types of Radiography
  1. Analog Radiography (Conventional SFS)
  1. Digital Radiography
    1. Digitizing conventional film
    2. Computed radiography (CR)
    3. Direct radiography (DR)
      It is one of the most modern imaging method in which selective window settings of some image enhance visualization of lung fields, mediastinum or bones as desired.
      1. Digitizing conventional film :Optic drum scanners/laser scanners can digitize conventional film radiographs.
      2. Computed radiography (CR)
        1. Phosphor plate CR (e.g. europium activated barium fluoride)
        2. Selenium detection CR → Excellent quantum efficiency considerable dose reduction possible.
        3. Large area, thin film transistor detector CR→ Rapid image, excellent resolution. 
Extra Edge

Although it is most mature radiographic technology and uses conventional radiographic equipment but employs reusable photostimulable phosphor or selenium plate (europium- doped barium fluorohalide) instead of conventional film cassette. Q


The phosphor plate can be reused once latent image has been erased by exposure to whole light.
  1. Major advantages of CRS: -
    1. Linear photoluminescence dose response, which is much greater than that of conventional film.
    2. Post processing of images possible.
    3. Advantage of image archiving and transmission.
    4. Excellent resolution
  • Direct radiography (DR)
  Computed Radiography(CR) Digital Radiography (DR)
Steps Required Prepare room
Load cassette
Position patient
Position tube
Perform exposure
Transport cassette
Process cassete
Assess image quality
Wrap up appointment with patient.
Prepare room
Position patient
Position tube
Perform exposure
Image is sent to viewing station
Assess image quality
Wrap up appointment with patient.
Image Acquisition Process A PSP plate within the cassette is exposed.
Latent image is captured in the plate as electrons in the phosphor are excited when exposed to radiation.
Cassette is placed in a reader to capture and analyse image data.
Laser and analog to digital converter translates signal to digital binary code.
Built in image capture plates used (No cassette required)
Large area, flat panel detectors with integrated TFT readout mechanisms, Integrated PSP plate scanning mechanism, or optic lens used to translate the analog image to digital image.
Image Quality Opportunities to improve image interpretation and diagnostic strength.
Potential for lower image noise and lower radiation exposure with appropriate system adjustments.
Opportunities to improve image interpretation and diagnostic strength.
Potential for lower image noise and lower radiation exposure with appropriate system adjustments.
May offer potential for better image quality with lower radiation dose than CR.
Potential Advantages Unlimited manipulation and positioning of image receptor for cross table projections is possible (useful in trauma) Relatively faster workflow due to elimination of cassettes.
Shorter turnaround time for viewing image.
Freeing of staff time.
Potential Disadvantages Slower, more complex workflow.
Possibility of repetitive motion injuries due to long term cassette handling
Higher costs.
RIS stands for the radiology information system and HIS stands for hospital information system. The RIS manages patient scheduling and tracking, examination billing, and receipt, display of radiology reports. 
  1. Picture archiving and communication system (PACS)
    A picture archiving and communication system (PACS) Q aims to replace conventional analogue film and paper, clinical request forms and reports with a completely computerized electronic network whereby digital images are viewed on monitors in conjunction with the clinical details of the patient and associated radiological report displayed in electronic format.
    1. In Medical imaging, picture archiving and communication systems (PACS) are computers or networks dedicated to the storage, retrieval, distribution and presentation of images. The medical images are stored in an independent format.
    2. The most common format for image storage is DICOM (Digital Imaging and Communications in Medicine).
      Types of images
    3. Most PACSs handle images from various medical imaging instruments, including ultrasound, magnetic resonance, PET, computed tomography, endoscopy, mammograms, etc
  1. PACS replaces hard-copy based means of managing medical images, such as film archives.
  2.  It expands on the possibilities of such conventional systems by providing capabilities of off-site viewing and reporting (distance education, telediagnosis).
  3. Additionally, it enables practitioners at various physical locations to access the same information simultaneously, (teleradiology).
  4. With the decreasing price of digital storage, PACSs provide a growing cost and space advantage over film archives.
  5. A PACS allows to store volumic exams and to reconstruct 3D images PACS is offered by virtually all the major medical imaging equipment manufacturers, medical IT companies and many independent software companies.
  6. A feature common to most PACS is to read the metadata from all the images into a central database. 
PACS stands for picture archiving and communication systems. These are the systems used by digital radiology departments to store, network, and view imaging studies. 

Contrast Studies:
Barium Studies
Barium studies form one of the still most commonly used radiological procedures.
  1. Barium swallow: dysphagia (to rule out stricture or mass)
  2. Barium meal: abdominal pain (to rule out gastric or duodenal ulcer disease)
  3. Small bowel follow-through: diarrhea or constipation (to rule out Crohn's disease or other small bowel pathologic conditions)
  4. Barium enema: rectal bleeding (to rule out a polyp or mass).
    1. Barium sulphate is inert and best for examination of GI tract, except in few settings like TO fistula and bowel perforation.
    2. However, compared to barium sulfate, the major advantage of aqueous contrast agents is their rapid absorption from the interstitial spaces and peritoneal cavity.
    3. This property makes them uniquely useful for examining patients with suspected TO fistula and perforation of a hollow viscus. No permanent deleterious effects from the presence of these aqueous contrast materials in the mediastinum, pleural cavity, or abdomen have been shown.
Extra Edge

Contraindications to barium studies of the upper GI tract include known or suspected perforation (use water-soluble agent) Q and the inability of the patient to swallow (use nasogastric tube).


Iodinated Contrast Media ( Iodine : particle ratio)
Ionic/ high osmolar: Na and meglumine salts of diatriazoate, iothalmate, urograffin, gastrograffin(3:2)

Non Ionic
  1. low osmolar: iohexol(3:1)
  2. Isoosmolar: iodixanol ( visipaque)(6:1)
Type of Iodinated contrast  Iodine particel ratio Osmolality concern e.g Comments
Ionic monomers 3:2Q High Osmolar Contrast Media (HOCM) Triiodinated benzoic ring with salts of Sodium and meglumine.
-Diatrizoate     -Iothalamate
-Metrizamide -Ioxithalamate
- Conventional.
- Not much preferred.
- Used for MCU (urethrographies), HCGs, etc.
Ionic dimers 6:2 or 3:1 LOCM -Ioxaglate - May be preferred
Non-ionic monomers 3:1 LOCM -Iohexol        -Iomeron
-Iopamidol   -Ipromide
-Ioversol       -Xenetix
- Most Preferred
- Safer than ionic contrast (especially in cases of renal failure).
Non-ionic dimers 6:1 LOCM -Iodixanol
-Much preferred
-The best for a case of patients with associated renal disease.
Contrast reactions:
  1. Idiosyncratic anaphylactoid reactions(DOC is adrenaline )
  2. Non-idiosyncratic reactions
Contrast Induced Nephropathy (CIN)
Contrast-induced nephrotoxicity (CIN) is a sudden deterioration in renal function following the recent intravascular administration of iodinated contrast medium in the absence of another nephrotoxic event.
There are no standard criteria for the diagnosis of CIN; criteria used in the past have included percent change in the baseline serum creatinine (an increase of variously 25% to 50%) and absolute elevation from baseline serum creatinine (e.g., an increase of variously 0.5 to 2.0 mg/dL). One of the most commonly used criteria has been an absolute increase of 0.5 mg/dL
The exact pathophysiology of CIN is not understood. Nephrotoxicity of contrast media is likely to be due to
  1. Decreased renal perfusion due to renal vasoconstriction (low BP, peripheral vasodilatation )
  2. Glomerular injury-manifests as proteinuria.
  3. Tubular injury-due to osmolarity, chemotoxicity, ischaemia.
  4. Contrast media precipitation of Tamm Horsfall protein that blocks tubules.
  5. Swelling of renal tubular cells causing obstruction
    Both osmotic and chemotoxic mechanisms may be involved, and some investigations suggest agent-specific chemotoxicity. 
    Symptoms: Usually asymptomatic. Creatinine peaks in 3-5 days. In severe oliguric patients: peaks in 5-7 days
Risk factors for CIN:
  1. Pre-existing renal impairment (S.creat > 1.3 mg/dl,GFR < 60 ml/min)
  2. Dehydration
  3. CHF
  4. Use of nephrotoxic drugs (NSAID, Aminoglycosides)
  5. Hypersensitivity disease (Multiple Myeloma)
  6. Hypertension
  7. Hyperuricemia (as in active gout)
  8. Proteinuria (> 0.5 gm/dl)
  9. DM, Age > 70 years
Prevention of Contrast induced nephropathy in high risk patients
  1. Avoidance of Iodinated Contrast Medium: In high risk patient it is best to avoid use of iodinated contrast media and the possibility of obtaining the necessary diagnostic information from another test, not using iodinated contrast medium (e.g., ultrasonography, magnetic resonance imaging), must be considered. In some clinical situations where the use of intravascular iodinated contrast medium may be necessary the lowest possible dose of contrast medium to obtain the necessary diagnostic information should be used.
  2. Contrast media selection: Increased osmotic overload on the diseased kidney is considered to be the major etiology of CIN so; these can be significantly reduced by substituting LOCM for the very hypertonic HOCM.
  3. Hydration: Adequate hydration is considered to be the single most effective way to prevent CIN. The ideal infusion rate and volume is unknown, but isotonic fluids are preferred (Lactated Ringer’s or 0.9% normal saline). One possible protocol would be 0.9% saline at 100 ml/hr, beginning 6 to 12 hours before and continuing 4 to 12 hours after intravascular iodinated contrast medium administration. Oral hydration has also been utilized, but with less demonstrated effectiveness. Pediatric infusion rates are variable and should be based on patient weight. 
  4. Sodium bicarbonate: It has been found to be useful in prevention from CIN according to some studies.
  5. N Acetyl Cystine: The role is controversial. There is evidence that it reduces serum creatinine in normal volunteers without changing cystatin-C (cystatin-C is reported to be a better marker of GFR than serum creatinine). This raises the possibility that N-acetylcysteine might be simply lowering serum creatinine without actually preventing renal injury. N-acetylcysteine should not be considered a substitute for appropriate pre-procedural patient screening and adequate hydration.
  6. Diuretics: Mannitol and Furosemide: There is no reported benefit and neither mannitol nor furosemide is recommended for CIN risk reduction.
  7. Other Agents: The evidence for other theoretically renal-protective medications, such as theophylline, endothelin-1, and fenoldopam is even less convincing. Use of these agents to reduce the risk of CIN is not recommended
Patient on metformin:
Remember: Metformin + Chronic Renal Insufficiency + I/v contrast = Lactic Acidosis
Category 1 Category 2  Category 3
Normal renal function with no known co-morbidities
No reason to discontinue Metformin
Normal renal function with known co-morbidities +, then suspend Metformin for 48 hrs
If the patient had normal renal function at baseline, was clinically stable, and had no intercurrent risk factors for renal damage (e.g., treatment with aminoglycosides, major surgery, heart failure, sepsis, repeat administration of large amounts of contrast media), metformin can be restarted
Renal dysfunction then suspend Metformin for 48 hrs & restart only if repeat KFT is normal

Iodinated contrast studies
  1. Sialography
    1. It is used to diagnose stones (sialolithiasis), chronic or recurrent inflammation, and tumors in parotid and submandibular glands.
    2. It is contraindicated in acute sialadenitis (parotitis) for fear of exacerbating the condition. Q
      Note: The parotid glands are the only salivary glands that contain lymph nodes.
  2. Urethrography
    1. Retrograde Urethrography/ Ascending urethrography
      1. Direct retrograde examination is appropriate, particularly if the anterior urethra is of paramount interest. Q
      2. Although an uncommon procedure in the female, examination of the male urethra by this technique is frequently done to evaluate urethral trauma or obstruction secondary to inflammatory disease or neoplasm.
      3. Opacification of the male urethra in retrograde fashion allows visualization of the anterior urethra but is usually accompanied by relatively poor filling of the posterior urethra because of the resistance encountered at the external sphincter. The anterior urethra will be well defined and distended and the level of the external sphincter clearly identified.
      4. ionic water soluble contrast material, like sodium and miglumine salts of diatriazoate or iothalamte are ideal contrast material.
Retrograde urethrography depict the membranous and anterior urethra better & is preferred approach for assessing inflammatory lesions & diverticuli.
  1. Voiding Cystourethrography / Micturating Cystourethrography/ Descending urethrograpy
    1. The primary indications for cystourethrography are to evaluate the presence of vesicoureteral reflux and to investigate abnormalities of the bladder neck and the posterior urethra.
    2. Functional assessment of bladder contractility and micturition is also possible using this technique. When radiographic complete assessment of the urethra is of primary concern, cystourethrography should be used in conjunction with a retrograde urethral study. Acute infection of the lower urinary tract is a contraindication to the procedure.
  • Indications:
    To demonstrate the various abnormalities in the neck of bladder and urethra: Q
  1. Recurrent UTI especially in children
  2. For complete assessment of cases of bladder diverticuli
  3. For demonstration of VUR
  4. For demonstration of bladder contractions and the control of micturition

Voiding cystourethrogram or micturating cystourethrogram demonstrates the prostatic urethra to best advantage as it is better distended than the membranous & anterior urethra. Q

  1. An MCU is indicated in all boys under 1 year of age with UTI.
  2. Any child who requires imaging of kidneys & or urinary tract for whatever reason, with the exception of trauma cases, should undergo a USG examination as the first investigation.
  3. MCU is however the definitive method of assessing the lower urinary tract. 
  4. It is necessary also in all boys to assess by MCU when there is any suspicion of urethral pathology.
  5. Congenital abnormalities affect both anterior & posterior urethra, the most common being hypospadias, which has little radiological importance.
  6. Posterior urethral valves is one of the most common GUT congenital abnormality in males causing obstructive uropathy. 
  7. USG usually strongly suggest the diagnosis & may detect complication like urinoma. This should however be followed by an MCU especially for confirmation and follow up.

In a male patient with pelvic trauma, the urethra should be evaluated with a retrograde urethrogram before placement of a bladder drainage catheter.

  1. Hysterosalpingography (HSG)
    1. Definition: Visualization of the uterine cavity and Fallopian tubes by using negative contrast media (normal saline in hydrosalpingosonography) or positive contrast media (Echovist in sonosalpingography and the iodinated water soluble contrast agent [diatriazoate] in HSG).
    2. Ideal time to perform HSG: Between 7th and 10th day of menstrual cycleQ, for following reasons:
      1. No risk of early pregnancy
      2. Isthmus is most easily distensible
      3. Tubal filling occurs readily.
    3. Indications for HSG:
      1. Infertility
      2. Recurrent miscarriage
      3. Congenital abnormalities
      4. Post-uterine and/or tubal surgery
      5. Abnormal uterine bleeding
      6. Evaluation after major pelvic trauma and/or surgery
      7. Prior to artificial insemination and in vitro fertilization, for tubal patency (other tubal patency tests are laparoscopic chromopertubation, CO2 insufflation and hydrosonosalphinography)
    4. Contraindications for HSG
      1. Pregnancy
      2. Acute endosalpingitis
      3. Bleeding
      4. Immediate pre and postmenstrual phases
      5. Recent untreated pelvic infection
      6. Tubal or uterine surgery within last 6 weeks
      7. Contrast medium sensitivity
      8. Recent D and C procedure
      9. Severe renal or cardiac disease
      10. Migrated IUCD.
  2. Myelography
    1. It is the radiographic investigation of the spinal canal for the diagnosis of space occupying and obstructive lesions and requires the contrast agent to be injected into the SUBARACHNOID spaceQ (which lies between pia mater and the arachnoid mater) usually following a lumbar puncture.
    2. Either a negative contrast agent like air or oxygen is used or more usually a positive non-ionic water-soluble low-osmolar, organic iodine compound. 
    3. Oily preparations like iophendylate (Myodil, Pamtopaque) is abandoned as it is known be toxic and causes chronic adhesive arachnoiditis. Amipaque (metrizamide) has replaced myodil (iophendylate) however best is nonionic media – Iohexol (Omnipaque) which commonly used today. Q
    4. Replaced by MRI.

Radiation Units

  1. Radiation units
    1. Conventional Units
      1. These are such units as the "three Rs":
        1)  Roentgen,                       
        2)   Rad                
        3)   Rem.
      2. New/ SI Units
        1) Coulomb’s /kg,               
        2)  Gray                 
        3)  Sievert
  1. Exposure Dose
    1. The unit of radiation exposure is the Roentgen (R), defined as an amount of x-rays or gamma rays that will liberate a charge of 2.58 x 10-4 C/Kg of air, under standard temperature and pressure; this quantity can be measured directly in an air chamber.
    2. The SI unit for radiation exposure is Coulombs/Kg.
    3. As a measure of exposure, Roentgen is independent of area or field size.
  2. Absorbed Dose
    1. The unit for measurement of the amount of energy deposited in tissue is the ‘rad’ or radiation absorbed dose. The unit rad is defined as the radiation necessary to deposit energy of 100 ergs in 1 gram of irradiated material.
    2. The SI unit for absorbed dose is Gray. One Gray is the amount of radiation necessary to deposit 1 joule of energy in 1Kg of material.
    3. 1 Gray= 100 Rads OR 1 Rad= 1 cGy.into a given mass of tissue.
  3. Dose Equivalent
    - They are quantities that can be measured and expressed in terms of the more fundamental physical quantities like energy.  Dose Equivalent, in the unit, sievert (Sv), is a quantity that expresses the relative biological impact of the radiation by including a radiation weighting factor (wR).  The relationship is:

 Dose Equivalent (Sv) = Ab Dose (Gy) x wR

The value of the radiation weighting factor (wR) is a characteristic of each specific type of radiation.

  1. Effective Dose
    Effective dose is becoming a very useful radiation quantity for expressing relative risk to humans, both patients and other personnel.  It is actually a simple and very logical concept.  It takes into account the specific organs and areas of the body that are exposed. The point is that all parts of the body and organs are not equally sensitive to the possible adverse effects of radiation, such as cancer induction and mutations. 
    For the purpose of determining effective dose, the different areas and organs have been assigned tissue weighting factor (wT) values.  For a specific organ or body area the effective dose is:
 Effective Dose (Gy) = Absorbed Dose (Gy) x wT

Extra Edge:
  1. The cell is vulnerable to radiation in the stage of mitosis (M), less so during synthesis (S) and relatively insensitive during resting periods.
  2. G2M interphase followed by M is when the cell is radiosensitive. Q
  3. Radiosensitivity of a cell also depends on its histological type and oxygenation of the tissues.
Radiation Side Effects
Radiation effects are classified as:
  • Acute or chronic
  • Involving somatic tissues or genetic information
  • Be directly proportional to dose i.e. deterministic (certainty) effects, or not directly proportional to dose i.e. stochastic effects.
  1. Somatic
    1. Certainty or deterministic effects
      1. Related with certainty to a known dose of radiation
      2. Dose threshold exists
      3. Severity is dose related
    2. Stochastic effects
      1. Random events without threshold
      2. Probability increases with dose
      3. Severity may not be dose related
  2. Genetic – are stochastic by their nature. 
  3. Somatic Deterministic effects
    1. Acute total-body irradiation - The data regarding the acute effects of total-body irradiation on humans come primarily from Japanese survivors of the atomic bomb, Marshall Islanders exposed to fall out radiation, victims of a few nuclear installation accidents, such as Chernobyl (in Ukraine) and patients in radiation therapy. Clinical manifestations depend on the total-body dose.
    2. At doses in excess of 100 Gy to the total body, death usually occurs within 24 to 48 hrs from neurologic and cardiovascular failure. This is known as the cerebrovascular syndrome. Because cerebrovascular damage cause death very quickly, the failure of other systems do not have time to develop.
    3. At doses between 5 and 12 Gy, death may occur in a matter of days, as a result of the gastrointestinal syndrome. The symptoms during this period may include nausea, vomiting and prolonged diarrhea for several days, leading to dehydration, sepsis and death.
    4. At total-body doses between 2 and 8 Gy, death may occur several weeks after exposure and is due to effects on the bone marrow, which results in the hematopoietic syndrome. The full effect of radiation is not apparent until the mature hematopoietic cells are depleted. Death from the hematologic damage occurs at about 20 to 30 days after exposure and the risk of death continues over the next 30 days. Clinical symptoms during this period may include chills, fatigue and petechial hemorrhage. The threshold for this syndrome is 1 Gy. 
Somatic/Acute/deterministic/non-stochastic effects
  1. Immediate effects (short term)
    1. Skin erythema
    2. Radiation sickness
    3. Acute radiation syndrome/sickness
  2. Delayed effects (long term)
    1. Radiation dermatitis                                                      
    2. Basal and squamous cell carcinoma skin
    3. Constrictive pericarditis                                                              
    4. Myocardial ischemia and fibrosis
    5. Radiation pneumonitis                                                
    6. Peritubular fibrosis in kidney
    7. Oesophagitis, gastroenteritis and colitis                    
    8. Intestinal ischemia, ulceration and atrophy
    9. Cataract                                                                            
    10. Retinal damage
    11. Radiation necrosis of brain                                          
    12. Transverse myelitis
    13. Infertility
  1. Chromosomal mutations                                                              
  2. Leukemias and tumors
  1. Threshold doses for some deterministic effects in case of acute total radiation exposure 
    1. 0.2 Gy – increase of number of the chromosomal aberration in bone marrow and lymphocytes
    2. 0.3 Gy – temporary sterility for man
    3. 0.5 Gy – depression of haematopoiesis
    4. 1.0 Gy – acute radiation syndrome
    5. 2.0 Gy – detectible opacities
    6. 5.0 Gy – visual impairment
    7. 2.5 – 6.0 Gy – sterility for woman
    8. 3.5 – 6.0 Gy – permanent sterility for man
    9. 3.0 – 10.0 Gy – skin injury
  2. Threshold doses for some deterministic effects in case of radiation exposure for many years
    1. 0.1 Gy – detectible opacities
    2. 0.2 Gy – sterility for woman
    3. 0.4 Gy – visual impairment
    4. 0.4 Gy – temporary sterility for man
    5. 0.4 Gy – depression of haematopoiesis
    6. 1.0 Gy – chronic radiation syndrome
    7. 2.0 Gy – permanent sterility for man

Radiation Protection


-Gieger Muller counter
  1. ALARA stands for As Low As Reasonably Achievable radiation dose. 
  2. The most often used and the best dosimeter is TLD (Thermo-luminescence dosimeter). The chemical content of TLD is lithium fluoride.
  3. Lead aprons (0.5 mm of lead) will reduce the intensity of scattered radiation by 90% and should be worn by all the workers associated with X-ray procedures regularly.

The basic principle of radiation principle is ALARA (As Low As Reasonably Achievable radiation dose). Q


  1. The permissible dose from man-made sources should not exceed 5 rad/year.
  2. Of the man made sources, the X-rays constitute the greatest hazard.
  1. QLatest AERB recommendations for maximum permissible dose for various groups are:
    1. Occupational exposure (Radiation workers)  → 100 mSv / 5 year( annual eq- 30 msev).
    2. Public (in general) → 1 mSv / year.
    3. Pregnancy  → 2mSv for declared term on the surface of her abdomen.
Examination Effective total dose (mSv)
Lumbar spine
Upper GI series
Barium enema
CT chest
CT abdomen
CT head
Bone Scan
2.8 to 4

Mammography uses lower kV (for higher image contrast) and higher mA (for shorter exposure times) compared with the technique for chest and abdominal examinations.
Medial-lateral oblique (MLO) and craniocaudal (CC). The direction of the x-ray beam is defined by the name of the view. For example, in CC views, the x-ray beam enters the cranial portion of the breast, traverses the breast, and exits on the caudal side of the breast onto the film. By convention, metallic markers indicating view type are placed closest to the axilla-laterally on the CC view and superiorly on the MLO view.
Compression views are often obtained to determine whether a density "presses out," meaning that on a compression view it is found to have represented a superimposition of normal breast tissue rather than an actual mass. Magnification views are obtained to better visualize calcifications or to better characterize a mass.
The American College of Radiology recommends that women begin getting mammograms at age 40 and annually thereafter.
Radiation does a woman receive from a routine screening mammogram is 0.2 rads (2 mGray) for two views of one breast

  1. US is an imaging technique that uses sound waves, generally in the range of 2 million-20 million cycles per second (2-20 MHz), well above the frequencies audible to humans or animals.
  2. A handheld transducer is applied to the body. This transducer both sends US waves into the body and receives reflected sound waves.
  3. The transducer's information is communicated via cable to the US scanner, and the data are rendered on a monitor.
  4. Ultrasound is inexpensive, quick, reliable and noninvasive and is an excellent initial investigation for a wide range of clinical problems. It is technically demanding and requires an experienced operator to maximise the potential of the examination.
  5. Despite the advances in technology, there are still problems with gas (which reflects sound completely) and obese patients, who are often unsuitable for ultrasound.
    Medical sonography employs frequencies between 2MHz and 20 MHz. Q
  6. By the virtue of piezoelectric effect in the ultrasound probe, one form of energy (electric energy) is converted in to another form (sound energy) the body /organs parts are imaged.
  7. It works on pulse echo principle and B-mode is used for transmission during all routine including abdominal ultrasonography.
  8. QReal-time B-scans allow body structures which are moving to be investigated.
    The piezoelectric effect occurs in a number of natural crystals including quartz, but the most commonly used substance is a synthetic ceramic, lead zirconate titanate.
  9. Percentage of the beam reflected at the tissue interface depends on, the tissue’s acoustic impedance and the angle of incidence of the beam.
  1. Methods of Display
    1. A – Mode (AMPLITUDE) : Amplitude of the returning signals is plotted in a graphical form against their distance from transducer / depth.
  1. B- Mode (BRIGHTNESS) : The amplitude of returning signals is given grey scale value based on a scale and is represented in the display to form a image of the scan plane.
  1. M-Mode (MOTION) : Detects any rhythmic motion occurring in the scan plane without any amplitude considerations.
  1. Regions with many acoustic interfaces reflect a lot of sound returning to the transducer. These are termed echogenic or hyperechoic and by convention are viewed as bright areas. Regions with few acoustic interfaces do not reflect many sound waves. These are termed hypoechoic and are viewed as dark areas.
  2. Lower US frequencies penetrate to greater depths, whereas higher US frequencies generally provide higher resolution. For a general examination of the abdomen, which requires large depths to see the liver, pancreas, and spleen, a 3- or 5-MHz transducer is a good choice. For a superficial examination, such as the scrotum or thyroid, a 10-MHz transducer is often used.
  3. Endovaginal probes are commonly used for gynecologic examinations and for evaluation of early pregnancies. They are usually 7.5-MHz probes. Endorectal probes are available for prostate imaging. They are generally in the range of 9 MHz.
  4. Posterior acoustic enhancement refers to the increased brightness seen beyond objects that transmit a lot of sound waves. Since fluid-filled cysts transmit a great deal of sound, the area beyond cysts often displays posterior acoustic enhancement.
  5. Posterior acoustic shadowing has the opposite effect-decreased brightness seen beyond objects that reflect a great deal of sound.
  1. Gallstones, which are echogenic, reflect a lot of sound, and shadowing is often seen in the tissue beyond the gallstones.
  2. Ultrasonography is investigation of choice for:
    1. Hydrocephalus in infantsQ
    2. CHPSQ
    3. Gall stonesQ
    4. Acute cholecystitis (although theoretically HIDA scan is best)
    5. Screening for Rotator cuff injuries (Best initial investigation) Q
    6. Renal colic in pregnancyQ
    7. Minimal ascites Q
    8. Obstetrics indications
    9. DDH
  3. TRUS (Transrectal ultrasonography)
  1. Transabdominal Ultrasound does not have the spatial resolution needed for identifying intraprostatic disease, for which transrectal or transurethral approach is necessary.
  2. TRUS is an excellent adjuvant to physical examination, it does not serve as a screening investigation. However, the combination of Digital Rectal examination (DRE) & serum PSA level is more sensitive then TRUS.
  3. But once suspected, prostatic carcinoma is most effectively confirmed by TRUS-guided needle biopsy.
    The staging accuracy of TRUS does not match the accuracies attainable by MRI, especially Endorectal coil MR.

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