Digital Radiology

Advances in computer and X-ray technology now permit the use of systems that employ sensors in place of X-ray films (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 films.

DIRECT IMAGING

- CCD or complementary metal oxide semiconductor (CMOS) detector used that is sensitive to electromagnetic radiation.

- Performance is comparable to film radiography for detection of periodontal lesions and proximal caries in noncavitated teeth.

INDIRECT IMAGING

- Radiographic film 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. 

DENTAL X-RAY TUBE

The dental X-ray tube is surrounded by a glass envelope that houses a vacuum.
The glass prevents low-grade radiation from escaping. The vacuum insures the protection of the equipment from catastrophic failure. Production of X-rays generates enormous amounts of heat; the vacuum prevents the risk of combustion and ensures the proper environment for conduction of electrons.

There are two separate energy sources, one that powers the energy potential between the cathode filament and the anode, and the other being
the controls for the cathode filament. The latter essentially is the on and off switch of the X-ray unit.

The cathode filament is heated which causes electrons to be emitted.

These electrons are then accelerated by the electrical potential of the circuit.

Between the two points is a tungsten target.
When electrons strike the target, X-rays are produced.

HALF-VALUE LAYER

- Property of a material whereas the thickness (mm) reduces 50% of a monochromatic X-ray beam.
- Half-value layer of a beam of radiation from an X-ray unit is about 2 mm of aluminum (Al).

PRIMARY RADIATION

- Is the main beam produced from the X-ray tube. 

SECONDARY RADIATION

- Produced by the collision of the main beam with matter which causes scatter.

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

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

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.

RELATIVE RADIO SENSITIVITY OF THE TISSUES

Radiosensitive (2500 r or less kills or seriously injures many cells)

Lymphocytes and lymphoblasts
Bone marrow (myeloblastic and erythroblastic cells)
Epithelium
Germ cells (testes and ovary)

Radioresponsive (2500-5000 r kills or seriously injures many cells)

Epithelium of skin and many appendages.
Endothelium of blood vessels
Salivary glands
Growing bone and cartilage.
Conjunctiva, cornea and lens of eye
Collagen and elastic tissue(fibroblasts themselves are resistant)

Radioresistant (over 5000 r are required to kill or injure many cells)

Kidney
Liver
Thyroid
Pancreas
Pituitary
Adrenal and parathyroids
Mature bone and cartilage
Muscle
Brain and other nervous tissue.

The numbers represent the minimum damaging doses; a gray and a sievert represent roughly the same amount of radiation:
• Fetus--2 grays (Gy).
• Bone marrow--2 Gy.
• Ovary--2-3 Gy.
• Testes--5-15 Gy.
• Lens of the eye--5 Gy.
• Child cartilage--10 Gy.
• Adult cartilage--60 Gy.
• Child bone--20 Gy.
• Adult bone--60 Gy.
• Kidney--23 Gy.
• Child muscle--20-30 Gy.
• Adult muscle--100+ Gy.
• Intestines--45-55 Gy.
• Brain--50 Gy.
 

Induction Agents in Anesthesia

Induction agents are medications used to initiate anesthesia, allowing for the transition from consciousness to an anesthetized state. The choice of induction agent depends on various factors, including the type of surgery, patient characteristics, and the desired speed of onset and recovery. Commonly used induction agents, their characteristics, and their applications.

Common Induction Agents

1. Propofol

   • Classification: Intravenous anesthetic
   • Onset: Rapid (30 seconds)
   • Duration: Short (5-10 minutes)
   • Advantages:
     • Smooth induction and emergence.
     • Low incidence of postoperative nausea and vomiting.
     • Provides sedation and amnesia.
   • Uses: Preferred for outpatient surgeries and day care procedures due to quick recovery.

2. Thiopental

   • Classification: Barbiturate
   • Onset: Rapid (30-60 seconds)
   • Duration: Short (5-10 minutes)
   • Advantages:
     • Effective for rapid induction.
     • Provides good cardiovascular stability.
   • Disadvantages: Can cause respiratory depression and has a longer recovery time due to redistribution.
   • Uses: Historically used for induction, particularly in emergency settings.

3. Etomidate

   • Classification: Non-barbiturate hypnotic
   • Onset: Rapid (30-60 seconds)
   • Duration: Short (5-10 minutes)
   • Advantages:
     • Minimal cardiovascular and respiratory effects.
     • Provides good hemodynamic stability.
   • Disadvantages: Can cause adrenal suppression with prolonged use.
   • Uses: Preferred in patients with cardiovascular instability or those at risk for hemodynamic changes.

4. Ketamine

   • Classification: Dissociative anesthetic
   • Onset: Rapid (1-2 minutes)
   • Duration: Moderate (10-20 minutes)
   • Advantages:
     • Provides analgesia and sedation.
     • Preserves airway reflexes and cardiovascular stability.
   • Disadvantages: Can cause hallucinations and emergence delirium.
   • Uses: Useful in pediatric patients, emergency settings, and for patients with asthma or reactive airway disease.

5. Sevoflurane

   • Classification: Inhalational anesthetic
   • Onset: Rapid (induction time varies based on delivery method)
   • Duration: Variable (depends on duration of administration)
   • Advantages:
     • Pleasant odor and rapid onset.
     • Minimal airway irritation.
   • Disadvantages: Requires inhalational delivery, which may not be suitable for all patients.
   • Uses: Commonly used for induction in pediatric patients and outpatient surgeries.

6. Isoflurane

   • Classification: Inhalational anesthetic
   • Onset: Moderate (depends on delivery method)
   • Duration: Variable (depends on duration of administration)
   • Advantages:
     • Provides good muscle relaxation and hemodynamic stability.
   • Disadvantages: Can cause respiratory irritation.
   • Uses: Often used in neurosurgery and for patients with specific cardiovascular concerns.

Factors Influencing the Choice of Induction Agent

1. Patient Factors:

   • Age, weight, comorbidities (e.g., cardiovascular or respiratory issues), and previous reactions to anesthetics.

2. Surgical Factors:

   • Type and duration of the procedure, anticipated blood loss, and the need for rapid recovery.

3. Desired Effects:

   • The need for analgesia, amnesia, and hemodynamic stability.

4. Setting:

   • Outpatient vs. inpatient procedures, emergency situations, and the availability of monitoring equipment.

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

1. Maxillary Central Incisors:
   • Vertical Angulation: +40 to +50 degrees
2. Maxillary Lateral Incisors:
   • Vertical Angulation: +40 to +50 degrees
3. Maxillary Canines:
   • Vertical Angulation: +45 to +55 degrees
4. Mandibular Central Incisors:
   • Vertical Angulation: -15 to -25 degrees
5. Mandibular Lateral Incisors:
   • Vertical Angulation: -15 to -25 degrees
6. Mandibular Canines:
   • Vertical Angulation: -20 to -30 degrees

Posterior Teeth

1. Maxillary Premolars:
   • Vertical Angulation: +30 to +40 degrees
2. Maxillary Molars:
   • Vertical Angulation: +20 to +30 degrees
3. Mandibular Premolars:
   • Vertical Angulation: -10 to -15 degrees
4. 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.