Radio unit 2 pt 3

robbypowell's version from 2015-04-24 10:54

conebeam ct

Question Answer
Who published “The use of cone-beam computed tomography in dentistry”? What is the point of this documentADA council of scientific affairs, Provide guidelines for CBCT use
Who must interpret a CBCT image?Dentist w/ appropriate training
What parts of a CBCT image must be interpreted?complete image (not just area of interest)
What 5 areas dealing with cone bean CT must dental students be educated in?When to take, How to take, Appropriate parameters, Rad Protection, & interpretation
When was computed tomography invented1972
When was the cone beam CT invented?1998
How are images captured by the cone beam CT?360 travel around head, 200+ planar images captured
What are the two unique features of the acquisition geometry of CBCT? What does this allow?Divergent cone-beam, single revolution
What positions can the patients be in in order to get a CBCT? What about a medical CT?CBCT seated, standing or lying down; med CT only lying down
What is the shape of the detector in cone beam CT? Why?FLAT (captures more scatter)
What are the exposure settings of a CBCT compared to medical CT? Compared to panoramic 2D radiographs?5mA & 120kV compared to med 90mA & 120kV (SIGNIFICANTLY HIGHER THAN PAN)
What are basis images?200+ planar images
What is a voxel?3d pixel (volumetric pixel)
What is the high and low spatial resolution of a CBCT? How does this compare to the line pairs of 2D radiographs?best CBCT = worst PSP
Why is CBCT used only to evaluate hard tissuecontrast resolution is low
What are the two types of peripheral CBCT artifacts? How can these be reduced?RADIOPAQUE STREAKING & SHADING ARTIFACT, reduce by INCREASING PROJECTION DATA
Why can’t we evaluate peri-implant bone on CBCT?artifacts
What is ring artifact? What causes it?lack of detector calibration
What width of bone is invisible on CBCT? Why?0.6 mm (b/c average of densities within space)
Why do lesions and tumors look worse on CBCT?exaggerates bone loss, b/c thinned sections don't show up
Why can’t CBCTs be used to detect caries?low contrast resolution
What is an implant guide?CBCT optimized implant guide for crown
Why are CBCTs useful in orthodontic and orthognathic surgery?Simulation, custom-made fixtures, 3-d printing
How many fractures of the jaw usually happen at a time? How can we best see them all?2, CBCT
What changes of the TMJ can be seen on a pan?ONLY MOST SEVERE
What developmental defect is easily evaluated using CBCT?Clefts
What might cause sinusitis that is easy to detect using CBCT?periodical component in maxillary sinus
How do we treat sleep apnea?airway opened
How does high resolution setting compare to the standard resolution setting in terms of radiation exposure?high resolution means more exposure
What is the one exception to smaller fields of view having smaller radiation exposure? Why?mandible has more than maxilla b/c mandible has salivary glands
Why does i-CAT have a lower CBCT radiation dose than a pan?because it is on the lowest resolution setting, which is rarely used
How much more radiation dose do children receive than adults?36% higher dosage

Among the manufacturers of CBCT units, what are the radiation exposure ranges for the following fields of view, and which company has the highest and lowest dosage for each

Question Answer
a. Large field of view3 - 17.58 X pan dosage (Galileos lowest, ProMax highest)
b. Medium5-16x pan dosage ( 3d ACCUITIMO highest, CS 9300 lowest)
c. Low0.3 - 10x ( CS 9300 lowest, 3d accuitimo highest)

advanced 2


Question Answer
What is digital subtraction? What is it normally used to observe? What else might it be used for?detects changes over time, usually bone height, but can be any change
Why is digital subtraction mostly used for research purposes?images are difficult to obtain
What is a customized jig? What is it used for?biteblock from impression material to ensure same bite relation
What is the only FDA approved handheld x-ray unit?NOMAD
What is the backscatter radiation shield of the NOMAD made from?Lead Acrylic
What is the diameter of the BID of the NOMAD? How does this compare to traditional wall mounted units? What about the focal spot size? Do these have clinical significance?6cm vs 8cm, 0.4mm vs 0.6 mm,
What are the three key manners in which the NOMAD must be used to ensure the clinician is not exposed to x-rays?perpendicular to operator, w/ shield close to BID, close as possible to patient
Why does the NOMAD have the same exposure level of x-rays if it has a longer exposure time than wall mounted unitsless kV and mA
What did the Dental staff doses with handheld dental intraoral x-ray units study determine?when used appropriately, NOMAD exposed staff to less radiation
What type of imaging are PSPs used forINTRA-ORAL (indirect digital media)
Why aren’t CCDs used much anymore?replaced by CMOS
When was the first CCD developed? PSP? CMOS?
Question Answer
What aspects of image acquisition of digital sensors are the same as analog film? What part is different?initial acquisition is the same, but then converted into digital image
The lower the number after the voltage is quantized in digital image acquisition, the ____ the color of the pixelDARKER
How is contrast resolution measured? What is it?BIT DEPTH
If I had a bit depth of 23, how many shades of grey would I have2 to the power of 23
That type of receptor has the lowest contrast resolution?PSP
What is spatial resolution? How is it measured?line pairs per mm
How do pixels affect spatial resolution?bigger pixels = less resolution
What is theoretical spatial resolution? Why is it impossible to achieve theoretical resolution?error in the system (electronic noise, diffusion of photons into scintillator, exchange across couplers)
What receptors have the highest spatial resolution? The lowest?Fim highest, PSP lowest
What 7 variables impact the spatial resolution of PSP?1. manufacturer 2. Construction 3. Scanner laser size (larger laser = higher spat res) 4. scatter of laser (more scatter = less spat res) 5. filtering of signal 6. digital manipulation of image 7. scan speed (high speed = low spat res)
What is the human eye’s spatial resolution? Contrast resolution?61 lp per mm, 60 shades of grey
What is detector latitude? What sensor has the highest?ability to produce diagnostic images over a range of exposure levels
What is the difference between active and physical size?active = image forming, physical = total size of detector
Why do direct digital sensors have active areas of less than 100%? How does the active area percentage change as the receptor gets smallerbecause they need space to store or transmit image
What percentage of the margins of a size 2 direct digital receptor is not active?25%
What is the active surface of a PSP?phosphor plate
What forms the latent image of a PSPelectrons trapped in phosphor plate
What causes the emission of visual light from a PSP? What color is this light?laser, blue-green light
Why can CMOS be used wirelessly? Why don’t we usually do that?low power usage; not used because of loss of signal
What is the problem with the decreasing size of pixels?requires greater exposure
If a PSP has white edges and discoloration, what should you do with it?REPLACE
For what reasons would we replace a PSP?phosphor rubbed off, disinfectant contaminated under phosphor
What three ways can we evaluate contrast resolution? What else can be measured with 2 of these?Step-wedge, Radiographic phantom, DDQAP (phantom & ddqap can measure spatial resolution)

What causes the following scanner errors, and what is the appearance of the resulting image

Question Answer
a. Belt slippingpsp moves through scanner too slowly = widened and elongated image
b. Photomultiplier rube filter light leakimage erased or with white streak
c. Vertical stripes (2 answers)carrier movement malfunction OR photomultiplier tube malfunction