Advanced Imaging Modalities Question And Answers

Advanced Imaging Modalities Essay Questions

Question 1. Define digital radiography. Briefly, describe the components of an intraoral digital radiography unit (RVG) and its image reconstruction technique.
Answer:

Digital radiography Definition: Digital radiography (DR) is defined as a diagnostic imaging technique that uses an image receptor called sensors to convert the image to digital analog that can be analyzed and stored in a computer.

Digital radiography Principle:

• When an X-ray beam strikes the sensor, an electronic charge is produced on the surface of the sensor which is then digitized.
• The data received by the sensor are translated to the analog form and transferred to the computer where it is transformed to digital form by an analog-to-digital converter (ADC).
• The image is displayed within 0.5-120 seconds and can be manipulated to enhance the appearance of the interpretation.

Digital radiography Components:

• A sensor is used to capture the image. Charge-coupled devices (CCDs) and the complementary metal oxide semiconductor (CMOS) are used in dentistry for intraoral imaging.
• A pixel (picture element) is a term used to describe a two-dimensional square area or cell on the silicon detector (sensor) that stores the electrons released radiation. The pixel corresponds to the silver halide grains in the X-ray film.
• The computer digitizes, processes, and stores information received from the sensor. The software stores the information in electronic format.
• It converts the electronic signals from the sensor into a range of gray shades to visualize on the monitor. The computer recognizes the pixels in a numerical form. The array of numbers for each pixel is between 0 and 255 (a total of 226 shades) which constructs the pixel grayscale resolution.
• The software manipulates the pixels to enhance contrast and density without additional radiation exposure.

Digital radiography Procedure:

• Sensor preparation: Sterile sensor should be placed intraorally similar to the conventional film placement. The sensors need to be wrapped with a disposable sleeve for infection control as they cannot withstand heat sterilization.
• Sensor placement: The sensor with a bite block attachment is placed in the oral cavity to aim the beam and sensors accurately. Paralleling or bisecting technique is used for exposure.

Magnetic Imaging Resonance

Digital radiography Advantages:

• The low radiation dose for the patient
• Image reconstruction capabilities
• Wider latitude
• Elimination of processing
• High signal-to-noise ratio.

Digital radiography Disadvantages:

• Higher initial cost
• The unknown lifespan of the detector.

Application in Dentistry:

• 3-D display of periodontal bone defects
• 3-D reconstruction of pulp canals to visualize.
  • Lateral canals and
  • Canal shapes
• To detect arthritic changes in condyle by surface reconstruction of TMJ
• A 2-D and 3-D visualization of anatomic structures for presurgical determination of implant sites.

Read And Learn More: Oral Medicine and Radiology Question And Answers

Question 2. Discuss the principle, technique, indications, advantages, and disadvantages of computed Tomography in detail.
Answer:

Computed Tomography Introduction:

• Computed tomography is a method of body-section radiography by which images of a layer within the structure is produced, while the images of structures above or below the plane of interest appear blurred.
• Sir Godfrey Hounsfield demonstrated the first computed tomography (CT) unit, in 1970.

Computed Tomography Principle:

• A collimated X-ray is focussed on the patient, the resultant rays are received and measured by a detector which transmits this information to a computer.
• The computer analyzes the signal and displays it on a monitor. For three-dimensional image construction, a three-dimensional array called a voxel (volume element) is useEach voxel has height, width, and depth.

Computed tomography Components:

• CT unit consists of an X-ray detector made up of crystalline cesium iodide (CsI) or cadmium tungstate (CdWO4). Thousands of these detectors are placed at 360° around the patient.
• The X-ray generator (gantry) revolves around the patient, and the detector is stable. Each detector is separated from the next by an interspace material.

Computed Tomography Image Quality:

• Spatial resolution is the ability to detect separate objects spaced very closely together. CT has a spatial resolution of about 15 line pairs/centimeter which is equivalent to an object size of 0.3 mm.
• CT has an excellent low contrast resolution and even slight differences in tissue density can be detected.

Computed Tomography Interpretations:

• Hyperdense dense lesions appear white
• Hypodense—low-density lesions appear dark
• Destructive and nondestructive nature of the lesions.

Magnetic Imaging Resonance

Computed tomography Advantages:

• CT allows image visualization in all dimensions—coronal, sagittal, or axial.
• CT is noninvasive, accurate, and painless.
• CT is helpful in revealing a detailed view of osseous structures.
• In traumatic cases, it is useful in revealing internal injuries.
• Eliminates superimposition seen in conventional extraoral radiography.

Computed tomography Disadvantages:

• Radiation dosage is very high →10 msv
• In TMJ disorders like articular disc derangements, articular discs are not seen clearly
• Very fine soft tissue details are obscured by bony structures in CT
• Beam scattering caused by metallic objects including implants will produce streak artifacts.

Question 4. Discuss the principle and clinical application of ultrasonography in oral diseases.
Answer:

• Ultrasonography (USG) is a specialized ima¬ging technique where sound waves with vibratory frequencies of 1-20 MHz are used for diagnostic purposes.
• A high-frequency transducer (7.5-10 MHz) is used for the diagnosis of oral lesions.

Ultrasonography Types:

1. B-mode ultrasonography: Reveals the lesion and its borders as a black and white image.
2. Color duplex ultrasonography: Reveals the tissue movements and blood flow.
3. Doppler ultrasonography: Differentiates the vessels.

Ultrasonography Principle:

• Scanners used in USG generate electrical impulses that are converted into high fre¬quency sound waves by a transducer and subsequently transmitted into tissues. Some waves penetrate the tissues, and some are reflected back to the transducer depending on the acoustic impedance of the tissues.
• Only the reflected waves (echoes) are reconverted to electrical energy, amplified, processed, and presented on a screen.

Ultrasonography USG Reading: Reading is based on echogenicity (the ability of a surface to echo or return a signal).

• Hyperechoic structures are “brighter” than their surroundings.
• Hypoechoic structures are less “bright” than their surroundings.
• Anechoic structures appear black. (No echoes).
• Isoechoic structures have the same den¬sities as its surroundings.

Calcified masses appear hyperechoic whereas clear fluid and blood appear as anechoic

Role of USG in the diagnosis of oral and maxillofacial regions:

• To analyze the normal and abnormal anatomical structures
• To diagnose:
  • Salivary gland diseases
  • Lymphadenopathy and lymphadenitis
  • Subcutaneous diseases
  • Tongue lesions
  • Fine needle aspiration biopsy (FNA).

Ultrasonography Advantages:

• Noninvasive, nonionizing
• No known deleterious bioeffects
• Rapid procedure
• Less expensive and easily reproducible
• Real-time guidance for needle aspiration
• Unaffected by metal artifacts such as dental restorations
• May be repeated as often as necessary.

Advanced Imaging Modalities Short Notes

Question 1. Image detectors used in intraoral digital radiography.
(or)
Intraoral sensors.
Answer: In intraoral digital radiography, a small sensor is used for recording the image instead of the radiographic film. (CCDs) and (CMOS) are the two detectors used for intraoral imaging.

Intraoral digital radiography Charge-coupled Devices:

• Charged coupled devices is a solid-state detectors comprising a radiosensitive silicon chip. The silicon CCD is divided into picture elements called pixels. The pixel is a small repository pack where the electrons released from the radiation exposure are store
• Pixel is the digital substitute for halide crystals in the X-ray film. The CCD is 640 x 480 individual pixels in size. When X-ray photons strike the CCD, an electronic latent image is produced which is transferred to the computer and displayed as a visible image on the screen.

Complementary Metal Oxide Semiconductor: They consist of a metal oxide semiconductor structure (silicon or silicon coated with phosphors).

The CMOS differs from CCD in the way that:

• The pixels are read
• It has 25% greater resolution
• Low cost and greater durability.

Question 2. Describe the types of digital imaging.
Answer:

Types of Digital Images:

1. Direct digital imaging:

• A sensor with a fiber-optic cable linked to the computer is placed into the patient’s mouth and exposed to X-radiation. The sensor receives the image and then transmits it to the computer.
• Within seconds of exposure, an image appears on the screen. The software is then used to enhance and store the mage.

Magnetic Imaging Resonance

2. Indirect Digital Imaging:

• Scanning the conventional radiographs: Uses a CCD camera and a computer. The CCD camera scans the available manual radiograph, digitizes and then presents it on the computer monitor.

• Storage phosphor imaging: It is a wireless imaging system and is also referred to as photostimulable phosphor imaging (PSP). A flexible, reusable phosphor-coated plate is placed into the mouth and exposed to x-radiation. After exposure, the PSP plate is removed and positioned in an electronic processor where a laser scans the plate. An image is generated and transferred to the computer.

Laser scanning takes 30 seconds to 5 minutes hence this type of digital imaging is less rapid.

Question 3. Discuss the advantages and disadvantages of intraoral digital imaging.
Answer:

Intraoral digital imaging Advantages:

• Superior grayscale resolution: Digital imaging uses up to 256 gray shades with the comparison of 16-25 gray shades of conventional imaging. So density and contrast enhancement is an important advantage.
• Reduced exposure to X-ray: The sensitivity of CCD reduces the radiation exposure from 50-90% to that required for conventional e-film.
• Image viewing: Chairside viewing of the image on the computer monitor within a moment after exposure.
• Elimination of film and darkroom
• Effective patient education tool: Patients can view the images along with the dentist which facilitates rapport and increases the patient’s understanding of diseases.
• Increased effectiveness: Image storage and professional communication are easier.

Intraoral digital imaging Disadvantages:

• Initial set-up cost
• Sensor size and thickness: This may cause discomfort or elicit the gag reflex.
• Infection control: The sensors are vulnerable to heat sterilization and hence require disposable plastic sleeves for infection control. These sleeves need to be changed between patients every time.
• Wear and tear: The PSP receptors are prone to wear and tear and hence limited longevity.
• Legal issues: The use of digital images as evidence in lawsuits is questionable.

Question 4. Describe subtraction radiography.
Answer: In dentistry, to detect small changes at the bone level like interproximal bone loss in periodontal diseases, temporal subtraction is used.

Question 5. Scintigraphy
(or)
Nuclear medicine
(or)
Radionuclide scan.
Answer:

• Nuclear medicine or scintigraphy is a technique that uses a carrier molecule to deliver a radionuclide or radiopharmaceutical agent or isotopes to target tissue to measure the Junction of that tissue.
• Radionuclide or isotope in an organism behaves identically to their stable counterparts because both are indistinguishable.
  It is the only technique that can detect and quantifies the biologic activity of cells in a tissue or organ. The common nuclide agent used is technetium (Tc).
• For bone studies, such as scan for metastatic tumor lesions, 99mTcMDP are used.
• For salivary tissues, 67Ga, 125I, and 18F are usePatients are imaged at various times after the radionuclide injection.
  Salivary glands are imaged after 30 minutes while bone scans are carried out after 2 hours waiting period
• This waiting period allows the cessation of normal metabolic activity before the isotope scans abnormal activity.

Question 6. Describe the equipment and technique in cone-beam computed tomography.
Answer: Cone-beam computed tomography (CBCT) is specially developed to evaluate maxilla-facial complex in three-dimensional imaging.

Cone-beam computed tomography Principle:

• A pyramidal or cone-shaped X-ray beam is directed towards an X-ray detector on the other side of the patient’s heaMultiple 2D projection images are captured in the selected field of view (FOV) according to the region of interest (ROI).
• Since one exposure completely covers the entire FOV, only one rotational motion of the gantry is adequate to capture the required information for image reconstruction.

Mechanism of CBCT:

• Production of X-rays
• Image detection
• Image reconstruction
• Image display.

Cone-beam computed tomography Technique:

• During CBCT rotation, a single exposure is made at specific intervals and provides projection images, called basis or projection images. The entire image series is known as the projection data
• Reconstruction software programs introduce the algorithms to these projection data to create a three-dimensional (3D) volumetric data set that provides the secondary reconstruction images in three orthogonal planes (axial, sagittal, and coronal).

Question 7. What are the advantages of using CBCT in dentistry?
Answer:

• CBCT equipment is low­priced than the CT machine.
• It provides high­contrast images and is hence useful in the imaging of the craniofacial bones.
• Rapid scan time leads to reduced artifacts.
• Produces images with high resolution in the range of 0.09 mm–0.4 mm.
• Radiation dose is less when compared to conventional CT.

Advanced Imaging Modalities Multiple Choice Questions

Question 1. The number of possible grayscale combinations/pixels is known as the bit depth of the image.

1. Voxel
2. The gradient measure of image
3. Sequence depth of image
4. The bit depth of image

Answer:  4. Bit depth of image

Question 2. The formula used to detect the number of possible grayscale combinations per pixel is.

1. N ²
2. 2N²
3. 2N
4. N ²

Answer: 3. 2N

Question 3. A transducer in ultrasonography is made up of.

1. Quartz crystal
2. Monoclinic crystals
3. Electron crystallography
4. Piezoelectric crystals

(Note: A transducer in ultrasonography is made up of piezoelectric crystals like lead zirconate titanate).

Answer: 4. Piezoelectric crystals

Question 4. The smallest element of a three-dimensional image is.

1. Voxel
2. Pixel
3. Tesla
4. Polygons

Answer: 1. Voxel

Advanced Imaging Modalities Viva Voce

Question 1. What is an analog image?
Answer: When X-ray photons hit the radiographic film, the details registered on the film is known as an analog image. Analog images consist of continuous spec¬trum of gray shades between the extremes of white and black.

Question 2. What is a digital image?
Answer: A sensor collects the analog details and converts it to a digital image in the computer processing unit. When an X-ray beam strikes the sensor, an electronic charge is produced on the surface of the sensor, which is digitized. The digital image is composed of picture elements called pixels. Each pixel has a discrete gray value.

Question 3. What is a sensor?
Answer: A sensor is a small detector placed in the mouth instead of radiographic film, to capture an image in digital radiography.

Question 4. Name a few image techniques that do not use radiation.
Answer: Ultrasonography, MRI, thermography.

Question 5. What is split-screen technology?
Answer: It is a unique feature on a digital radiography system that allows the operator to view and compare multiple images on the same screen. This feature is helpful for comparison and evaluation of the progression of caries or periodontal diseases.

Question 6. MR or MRI contrast materials.
Answer:

• Ferromagnetic
• Paramagnetic [Lanthamide-Gadolinium diethylenetriamine pantothenic acid (Gd- DTPA)]
• Super magnetic.

Question 7. What is thermography?
Answer:

• It is a diagnostic method in which small electronic probes called thermistors, liquid crystals or infrared scanners are used to record temperatures in various structures and detect abnormal conditions.
• Abnormal conditions like inflammation or malignant tumors are associated with abnormal blood flow and result in different temperature patterns.

Question 8. What is real-time imaging?
Answer: Imaging techniques that allow the perception of motion are known as real-time imaging.

Question 9. Name a few radionuclide tracers.
(or)
Name some radioisotopes used in nuclear medicine.
Answer: Iodine (¹³¹I), gallium (⁶⁷G), Technetium 99m (^99mTc), selenium (⁷⁴Se).

Question 10. What is the coronal axis?
Answer: It is an imaginary vertical plane that separates the body into anterior and posterior halves and runs perpendicular to the ground.

Question 11. What is the sagittal axis?
Answer: It is an imaginary axis that divides the body into the right and left half, and runs perpendicular to the ground and through the middle of the body.

Question 12. What is an axial plane?
Answer: It is an imaginary horizontal axis that divides the body into superior and inferior aspects and runs parallel to the ground.

Question 13. What is DICOM?
Answer: The acronym DICOM refers to Digital imaging and communication in medicine. The universal format for handling, storing, and transmitting three-dimensional images is called as DICOM data.

Question 14. State a few differences between CT and CBCT.
Answer:

Advanced Imaging Modalities Highlights

• Advances in radiographic technology substi¬tuted film mages with a filmless radiographic system known as digital imaging in 1987. Similarly, two-dimensional images are complemented by the development of three-dimensional digital imaging which allows the viewing of oral and maxillofacial structures to provide accurate diagnostic information.
• Nonionizing imaging techniques that use ultrasound and magnetic field are also playing a great role in this er also, to enhance the structural and functional details, the use of radioisotopes and contrast agents plays a considerable role.