NEET MDS Lessons
Radiology
Radiation Biology
-X- and g -rays are called sparsely ionizing because along the tracks of the electrons set in motion, primary ionizing events are well separated in space.
Alpha-particles and neutrons are densely ionizing because the tracks consist of dense columns of ionization.
X-rays, gamma rays, electrons, and protons are all low LET forms of radiation in that their density of ionization is sparse. In general, they penetrate tissues deeply and result in less intracellular radiation injury.
High LET forms of radiation, such as heavy nuclear particles (e.g. fast neutrons), penetrate tissues less deeply and cause more radiation injury to biologic material.
Cells are most sensitive to Radiation when:
- they are undifferentiated.
Exceptions to this Law:
- lymphocyte
- Oocyte
X-rays and gamma rays show latent injury that is residual tissue damage even after the initial radiation reaction is subsided.
Proteins tend to be more radiosensitive than carbohydrates and lipids.
Most radiosensitive tissue-small lymphocyte
Most radioresistant tissue- brain
Embryonic, immature or poorly differentiated tissues are more easily injured by radiation, but they also show greater recovery properties.
All cells show increased susceptibility to radiation at the time of mitotic division and if the cells are irradiated during the resting phase, mitosis is delayed or inhibited.
- In general, cells are most radiosensitive in late M and G2 phases and most resistant in late S.
- for cells with a longer cell cycle time and a significantly long G1 phase, there is a second peak of resistance late in G1
- the pattern of resistance and sensitivity correlates with the level of sulfhydryl compounds in the cell. Sulfhydryls are natural radioprotectors and tend to be at their highest levels in S and at their lowest near mitosis.
- To produce its effect. Oxygen must be present during the radiation exposure or at least during the lifetime of the free radicals (10-5 sec).
- Mandible is more ssceptible to radiation injury than maxilla due to the denser structure and poorer blood supply.
- Salivary glands though an organ with a low turnover rate, was unusually sensitive to radiation
- Liposarcoma tumors are the most radiosensitive soft tissue tumors
- Exophytic tumors are usually more easily controlled with radiation while infiltrative and ulcerative lesions are more radioresistant.
The infiltrative and ulcerative lesions are more likely to be larger than clinically apparent and contain a larger proportion of hypoxic cells.
Bisecting angle technique
Bisecting angle technique is a method used in dental radiography to obtain radiographs of teeth and surrounding structures. This technique involves positioning the X-ray beam perpendicular to an imaginary line that bisects the angle formed by the long axis of the tooth and the film or sensor. Here are the general guidelines for angulations when using the bisecting angle technique:
Anterior Teeth
- Maxillary Central Incisors:
- Vertical Angulation: +40 to +50 degrees
- Maxillary Lateral Incisors:
- Vertical Angulation: +40 to +50 degrees
- Maxillary Canines:
- Vertical Angulation: +45 to +55 degrees
- Mandibular Central Incisors:
- Vertical Angulation: -15 to -25 degrees
- Mandibular Lateral Incisors:
- Vertical Angulation: -15 to -25 degrees
- Mandibular Canines:
- Vertical Angulation: -20 to -30 degrees
Posterior Teeth
- Maxillary Premolars:
- Vertical Angulation: +30 to +40 degrees
- Maxillary Molars:
- Vertical Angulation: +20 to +30 degrees
- Mandibular Premolars:
- Vertical Angulation: -10 to -15 degrees
- Mandibular Molars:
- Vertical Angulation: -5 to -10 degrees
Key Points
- Positioning: The film or sensor should be placed as close to the tooth as possible, and the X-ray beam should be directed perpendicular to the bisecting line.
- Patient Comfort: Ensure that the patient is comfortable and that the film or sensor is properly stabilized to avoid movement during exposure.
- Technique Variability: The exact angulation may vary based on the individual patient's anatomy, so adjustments may be necessary.
Age Groups and Radiographs
-
Age 2:
- Anterior IOPA's: 2
- Posterior IOPA's: 4
- Bitewings: 2
- Total Films: 12
-
Age 8:
- Anterior IOPA's: 8
- Posterior IOPA's: 4
- Bitewings: 2
- Total Films: 14
-
Age 8 (another entry):
- Anterior IOPA's: 8
- Posterior IOPA's: 8
- Bitewings: 2
- Total Films: 20
Summary of Total Films by Type
-
Anterior IOPA's:
- Age 2: 2
- Age 8: 8
- Age 8 (another entry): 8
- Total Anterior IOPA's: 18
-
Posterior IOPA's:
- Age 2: 4
- Age 8: 4
- Age 8 (another entry): 8
- Total Posterior IOPA's: 16
-
Bitewings:
- Age 2: 2
- Age 8: 2
- Age 8 (another entry): 2
- Total Bitewings: 6
Overall Total Films
- Total Films for Age 2: 12
- Total Films for Age 8 (first entry): 14
- Total Films for Age 8 (second entry): 20
- Grand Total Films: 12 + 14 + 20 = 46
Common Problems in Film Processing
1. Light Radiographs
- Causes:
- Under Development:
- Temperature too low
- Time too short
- Depleted developer solution
- Under Exposure:
- Insufficient milliamperage
- Insufficient kVp
- Insufficient exposure time
- Film-source distance too great
- Film packet reversed in the mouth
- Under Development:
2. Dark Radiographs
- Causes:
- Over Development:
- Temperature too high
- Time too long
- Accidental exposure to light
- Improper safe lighting
- Developer concentration too high
- Over Exposure:
- Excessive milliamperage
- Excessive kVp
- Excessive exposure time
- Film-source distance too short
- Over Development:
3. Insufficient Contrast
- Causes:
- Improper processing conditions (under or over development)
- Depleted developer solution
- Contaminated solutions
4. Film Fog
- Causes:
- Excessive kVp
- Improper safe lighting
- Light leaks in the darkroom
- Contaminated developer solution
5. Dark Spots or Tines
- Causes:
- Contaminated solutions
- Film contaminated with developer before processing
- Film in contact with tank or another film during fixation
6. Light Spots
- Causes:
- Insufficient washing
- Film contaminated with fixer before processing
- Film in contact with tank or another film during development
7. Yellow or Brown Stains
- Causes:
- Insufficient washing after fixation
- Depleted fixer solution
- Contaminated solutions
8. Blurring
- Causes:
- Movement of the patient during exposure
- Movement of the X-ray tube head
- Double exposure
- Misalignment of the X-ray tube head (cone cut)
9. Partial Images
- Causes:
- Top of film not immersed in developing solution
- Film in contact with tank or another film during processing
10. Emulsion Peel
- Causes:
- Excessive bending of the film
- Improper handling of the film
11. Static Discharge
- Causes:
- Static discharge to film before processing (results in dark lines with a tree-like image)
12. Fingerprint Contamination
- Causes:
- Fingerprint contamination during handling of the film
13. Excessive Roller Pressure
- Causes:
- Excessive roller pressure during processing can lead to artifacts on the film.
Digital Radiology
Advances in computer and X-ray technology now permit the use of systems that employ sensors in place of X-ray ?lms (with emulsion). The image is either directly or indirectly converted into a digital representation that is displayed on a computer screen.
DIGITAL IMAGE RECEPTORS
- charged coupled device (CCD) used
- Pure silicon divided into pixels.
- Electromagnetic energy from visible light or X-rays interacts with pixels to create an electric charge that can be stored.
- Stored charges are transmitted electronically and create an analog output signal and displayed via digital converter (analog to digital converter).
ADVANTAGES OF DIGITAL TECHNIQUE
Immediate display of images.
Enhancement of image (e.g., contrast, gray scale, brightness).
Radiation dose reduction up to 60%.
Major disadvantage: High initial cost of sensors. Decreased image resolution and contrast as compared to D speed ?lms.
DIRECT IMAGING
- CCD or complementary metal oxide semiconductor (CMOS) detector used that is sensitive to electromagnetic radiation.
- Performance is comparable to ?lm radiography for detection of periodontal lesions and proximal caries in noncavitated teeth.
INDIRECT IMAGING
- Radiographic ?lm is used as the image receiver (detector).
- Image is digitized from signals created by a video device or scanner that views the radiograph.
Sensors
STORAGE PHOSPHOR IMAGING SYSTEMS
Phosphor screens are exposed to ionizing radiation which excites BaFBR:EU+2 crystals in the screen storing the image.
A computer-assisted laser then promotes the release of energy from the crystals in the form of blue light.
The blue light is scanned and the image is reconstructed digitally.
ELECTRONIC SENSOR SYSTEMS
X-rays are converted into light which is then read by an electronic sensor such as a CCD or CMOS.
Other systems convert the electromagnetic radiation directly into electrical impulses.
Digital image is created out of the electrical impulses.
1. Postero-Anterior (PA) View of Skull
- Head Position: Centered in front of the cassette; canthomeatal line parallel to the floor. For cephalometric applications, the canthomeatal line is 10° above the horizontal, and the Frankfort plane is perpendicular to the film.
- Projection of Central Ray: Passes posterior to anterior, perpendicular to the film.
- Important Features:
- Used to examine the skull for disease, trauma, and sinuses.
- Best for viewing the coronoid process; a PA view with a 10° tilt is called the Caldwell projection.
2. Lateral Skull or Cephalometric View
- Head Position: Left side of the face near the cassette; midsagittal plane parallel to the film.
- Projection of Central Ray: Directed towards the external auditory meatus, perpendicular to the film and midsagittal plane.
- Important Features:
- Assesses facial growth.
- Reveals soft tissue profile.
- Surveys skull and facial bones for disease and trauma.
3. Water's Projection
- Head Position: Sagittal plane perpendicular to the film; chin raised so the canthomeatal line is 37° above horizontal.
- Projection of Central Ray: Passes through the maxillary sinus.
- Important Features:
- Also known as Occipito-mental projection (variation of PA view).
- Best for demonstrating zygoma fractures, paranasal sinuses, and nasal cavity.
- Shows the position of the coronoid process between the maxilla and zygomatic arch.
4. Submentovertex (SMV) View
- Head Position: Head and neck extended backward; vertex of the skull at the center of the cassette.
- Projection of Central Ray: Directed towards the vertex of the skull.
- Important Features:
- Also called BASE, FULL AXIAL, or JUG HANDLE VIEW.
- Best for viewing the base of the skull and zygomatic arch fractures.
- Contraindicated in patients with cervical spondylitis.
- For viewing zygomatic arches, exposure time is reduced to one-third of that used for the skull.
5. Reverse Towne's View
- Head Position: Canthomeatal line oriented 25-30° downward.
- Projection of Central Ray: Directed towards the occipital bone.
- Important Features:
- Frankfort plane vertically oriented and parallel to the film.
- Best for viewing condylar neck fractures.
- Condyles are better visualized if the patient opens their mouth widely.
6. Lateral Oblique Mandibular Body Projection
- Head Position: Tilted towards the side being examined; mandible protruded.
- Projection of Central Ray: Directed towards the first molar region.
- Important Features:
- Demonstrates the premolar and molar region.
- Best for viewing the inferior border of the mandible.
7. Lateral Oblique Mandibular Ramus Projection
- Head Position: Tilted towards the side being examined; mandible protruded.
- Projection of Central Ray: Directed posteriorly towards the center of the ramus.
- Important Features:
- Often used for examining third molar regions of the maxilla and mandible.
- Provides a view of the ramus from the angle to the condyle.
Radiographic films used in Dentistry
1. Intraoral Periapical (IOPA) Film
- Size 0:
- Dimensions: 22 x 35 mm
- For: Small children
- MPD (Maximum Permissible Dose) for whole body: 0.1 Rem in 1 year
- Size 1:
- MPD for gonads/bone marrow: 0.5 Rem in 1 year
- Size 2:
- Dimensions: 24 x 40 mm or 32 x 41 mm
- For: Anterior projections and adults
- MPD for gestation period in relation to the fetus: 5 Rem
- MPD for skin: 0.5 Rem in 1 year
- Radiation Exposure:
- Mean exposure from one IOPA: 300 mR
- Mean exposure from improved dental X-ray techniques: as low as 110 mR
2. Bitewing Film
- Size 0:
- For: Very small children
- Size 1:
- For: Children
- Size 2:
- For: Adults
3. Occlusal Film
- Size:
- 3 times larger than size 2 film (57 x 76 mm)
- Used for capturing larger areas of the dental arch.
4. Screen Film
- Size:
- 8 x 10 inches
- Used for extraoral projections in conjunction with an intensifying screen.
Additional Information
- Erythema Dose: The amount of radiation necessary to produce a noticeable skin reaction, typically 300-400 R.
- ALARA Principle: Stands for "As Low As Reasonably Achievable," emphasizing the importance of minimizing radiation exposure.