CT midterm

Question Answer
what is the process of obtaining info to create images called data acquisition
what part of the CT machine controls data acquisition, processing, image viewing and display, and storage of data system console/computer
what does DAS stand for data acquisition system
what are the 3 functions of the DAS amplifies detector signal, converts analog signal to digital, and transmits digital signal to computer
what DAS method is used in gen 1-4 scanners slice by slice/step and shoot/axial/translate-rotate, table moves to imaging location and remains still while the X-ray tube rotates, prevents winding up of high voltage cables and creates PERPENDICULAR SLICES
what DAS method is used in gen 6 scanners SDCT helical/spiral/volumetric, continuous movement of the patient/table through the gantry as the tub stayed on rotating in one direction around the patient creating a volume of data instead of a single slice, the slices are at a slight tilt
what DAS method is used in gen 7 scanners MDCT helical/spiral/volumetric, same as SDCT but more than 1 row of detectors is being used
what 3 things does informed consent consist of describing the procedure, explaining the risks/benefits/uncertainties, the patient's acceptance or nonacceptance of the procedure
is informed consent required by all states no
informed consent may be used too indicate a patient's ______ of the procedure and its complications understanding
informed consent must be obtained for what 2 things biopsy or drainage procedure
describe a patient who can and cannot give informed consent can – appropriate age and of sound mental capacity and gives it voluntarily….. cannot – if intoxicated, unconscious, or sedated or forced into signing something
what 2 lab tests test for kidney function and give their normal values BUN – 7-25 mg/dl… creatinine – .6-1.7 mg/dl
what 2 lab tests test for blood clotting factors and give their normal values PT – 11-14 sec…. PTT – 25-35 sec
what is the normal level for a lab platelets test 150,000-400,000 mm^3
what factors go into a GFR test race, sex, age, creatinine level… only good for that moment
what determines beam width in MDCT # slices/rotation x slice thickness
the beam width and detector width are ______ in SDCT equal
what restricts the path of the X-rays and reduces scatter and helps to define slice thickness in SDCT collimators
what type of collimators is before the patient and only allows the passage of X-rays in the selected slice, helps determines patient dose pre patient collimators
what type of collimator restricts unwanted X-rays from entering the detector assembly and helps to define slice thickness and reduces scatter from entering the detectors post patient collimators
what is the controlling factors of slice thickness in SDCT collimators
what is the controlling factor of slice thickness in MDCT collimators and detector width/configuration
what restricts the passage of low energy X-rays and allows passage of higher energy X-rays, helps create a uniform beam intensity which helps minimize artifacts filters
do filters help to lower patient dose yes
what is used to capture the X-ray beam from the patient and convert it into a signal which can then be turned into a binary code detector
what detectors is packed closely together with no interspaces, compressed gas, 60-87% efficiency, only detects X-rays entering the long axis, USED IN 3RD GEN SCANNERS xenon gas detectors
what detectors come in various widths, are 99-100% efficient, not packed closely together, detect X-rays at various angles, and require a small gap between detectors to avoid crosswalk between detectors, USED IN 3-4 AND ALL NEW GENS solid state detectors
what detectors are USED IN 6TH GEN that is a single row of detectors, anatomy covered = since increment x # of slices single detector row system
what detectors are USED IN 7TH GEN that is multiple rows of detectors, can be variable or uniform arrays, allows for more slices per gantry rotation multi detector row system
what type of effects are for which the probability (rather than severity) of the effect occurring depends upon dose… low dose is better, late effects as they occur years later, probability of effects increase as dose increases, no dose threshold stochastic effects like leukemia, cancer, hereditary effects
what type of effects are the effects for which the severity of the effect (rather than probability) increases w increasing dose for which there is a threshold dose, below the threshold dose these effects do not occur deterministic/nonstochastic effects like skin erythema, pericarditis, cataracts, nausea, CNS damage, sterility, death
what type of computers handle data composed of constantly varying electrical currents/impulses, operate on continuous physical qualities, has varying amplitudes analog computers
what type of computers handle data composed of definition quantities of current, operate on digital data, has 2 distinct amplitudes, can reads 1s and 0s, in binary format digital computers
what are devices used to enter info into the computer for processing called like keyboards, mouse, camera, CT detectors, MRI coils input devices
what are devices used to display info generated in a computer called like video monitors, graphic displays, printers, voice output output devices
who developed the math of image reconstruction by back projection, won Nobel Peace prize in 79 w Hounsfield, studied nuclear physics Cormack
who is the father/inventor of CT, worked for EMI on radar systems and computer tech, his first invention only imaged brains, 1971 pt w suspected brain lesions scanned 1st time ever, shares nobel peace prize w cormack Hounsfield
who developed the 1st whole body scanner in 74, revolutionized scanning bc it allows for more than just scanning heads, studied dang near everything Ledley
what is the MSAD (multiple scan average dose) total dose is the central slice radiation does plus the scatter overlap
the MSAD will be greater than the CTDI if there is overlap
the MSAD will be less than the CTDI if there are gaps
the MSAD will be equal to the CTDI if there are no overlaps or gaps
what is the formula for MSAD CTDI (slice thickness/patient table increment)
what is the CTDI (CT dose index) calculation of the dose when there are no overlapping or gapped slices, measurement of exposure per slice and independent of scan length
thinner slices have greater penumbra = greater _____ dose
what is the DLP (dose length product) accounts for the irradiated length of the scan
the DLP value is affected by variance in the patient ______ anatomy
what is the formula for DLP CTDI x scan length
how much of the radiation dose for the population is from CT scans 67%
name some things that increase patient dose inc. in mas, inc. in kvp, pitch less than 1, larger patients, repeating scans, beam geometry/collimation, detector efficiency, slice width/spacing, poor filtration, not properly using collimation
CT dose is more ____ than general radiography uniform
why is CT dose more uniform than general radiography because the CT beam is heavily filtered before entering the patient and because CT exposure comes from all directions which creates a more uniform exposure
body scans are _____ uniform than head scan because the uniformity of the dose decreases as the SFOV and patient thickness increases less
if you are able to use a _____ to protect from scatter radiation shield
what are some ways to reduce radiation from CT dose reduce extra images, use automated tube current modulation, adjust mAs after you've adjusted kvp, avoid inc. kVp, increase pitch, limit use of thin slices,
what are some ways to reduce radiation from CT dose for a pediatric patient limit mAs, angle tube away from eyes, routine maintenance checks, use correct slice thickness, scan without overlaps, use immobilizers to reduce rescanning, customize exams based on body part, shield
what are the 3 types of artifacts physics based, patient base, equipment induced
what is a distortion/error in an image that is unrelated to the subject being studied, any discrepancy between the recommend CT #s int he image and the true attenuation coefficients of the object artifact
what type of artifact is when a patients anatomy is out of the SFOV , causes anatomy outside of SFOV to contribute to the attenuation and hardens the beam but is ignored in image recon process, LEAVES WHITE AREA OF SHADING OR STREAKS out of field artifacts
is it easy to fix out of field artifacts and how can you fix them no it's not easy because you can't shrink a patient, and to help control it ensure all anatomy is inside SFOV, use proper centering and utilize proper SFOV
what type of artifact results from motion patient motion artifacts
what type of motion artifact can be controlled by the patient like swallowing or breathing voluntary motion
what type of motion artifact is what the patient cannot control like peristalsis or cardiac motion involuntary motion
what appearance does motion artifact have shading or ghosting, streaking or blurring
what type of equipment induced artifacts looks like concentric rings that occurs because of a bad detector, occurred in 3rd gen scanners ring artifacts
how can you reduce ring artifacts recalibrate bad detector and if that doesn't work call service
what type of artifact is an increase in the mean energy of the beam as it passes thru the pt, beam is harder bc lower energy photons are absorbed by the tissues leaving the higher energy photons to be captures by the detectors beam hardening artifact
what does beam hardening artifact look like dark bands or streaks or periphery looks lighter than the center (cupping)
what results from the mathematical averaging go a voxel of tissue attenuations, more than one tissue is contained in the voxel partial volume averaging
what type of artifact i when a dense object lies to the edge of a FOV and only a few views are obtained in a 360 degree rotation, too few views are obtained to accurately describe the object partial volume artifact
how can you reduce partial volume artifacts use thinner slices
what type of artifact is star shaped streaks on the image, there is no transmission of info to the detector thus a white area will appear on the image metallic artifacts
how can you reduce metallic artifacts inc. kvp to penetrate metal (only reduces.. doesn't remove it), remove external metal objects, reduction software, use gantry tilt or scanning ranges to avoid metal
what is the general rule of thumb for imaging pregnant women unless the benefits outweigh the risks, don't scan women in the 1st trimester
can a pregnant woman continue to breastfeed after having CT contrast yes because the amount of contrast that the infant would ingest is VERY SMALL compared to what was injected
what is the HU for bone 1000
what is the HU for water 0
what is the HU for air -1000
what is the central value of the WW that is set equal to the CT # of the tissue os interest window level
what is the range of CT #s that determines how many shades of gray will be presented on an image window width
when do you want a wide WW when imaging bone, long scale contrast/low contrast
when do you want a narrow WW when imaging soft tissue, short scale contrast/high contrast
what type of data is from the detectors the has not been assigned a HU raw data
what type of data is processed raw data that has been assigned a HU image data
what type of data do we save in PACS image data
what is the mathematical method of estimating the value of an unknown by using known values on either side interpolation
when does interpolation occur before filtered back projection in a spiral image
what is the ratio of the distance the table travels per 360 degrees rotation in 6th gen scanners, the formula = I/S (table increment/slice thickness) pitch
a pitch of 1 means the table speed is _____ to the slice thickness equal
a pitch greater than one means that data is being ______ missed
a pitch less than one means that _____ is occurring oversampling
what is the formula for pitch in 7th gen scanners beam pitch = table increment/#slices per rotation x slice thickness… P=I/BW
increasing pitch will ____ scan times but sacrifices image noise decrease
increasing the pitch will _____ the dose to the patient decrease
what type of artifact may occur if the pitch is raised too much streak artifact due to not having enough points to sample from
how do you test for slice thickness accuracy use a phantom that has a step wedge, ramp or spiral and contains objects with known measurements, performed semiannually
what parameters does a slice thickness test have to be within to be considered accurate for a slice 5mm or larger, plus or minus 1 mm in difference… for a slice less than 5 mm, plus or minus .5 mm in difference
what is the purpose of performing a CT tube warmup to prevent thermal shock
_____ size determines spatial resolution pixel
the smaller the pixel the ____ the spatial resolution greater
what is the formula to determines pixel size FOV/matrix
what is a picture element pixel
what makes up a matrix pixels
what modality has the largest matrix mammo
what modality has the smallest matrix nuc med
what are that advantages of MDCT the reconstruction of an image can be made anywhere in the block of data, you can recon the overlapping images, slice thickness can be changed retrospectively, more images per 360 degree rotation
what beam geometry does 7th gen scanners use cone beam
what beam geometry does 6th ten scanners use fan beam
what is the difference between filtered back projection and iterative reconstruction FB – uses raw data & puts a filter on it to enhance/suppress certain things in the image, more specific w what it focuses on than ASIRASIR – lower dose & an algorithm & it starts w an assumed image then computes proj. to update it, enhances everything
what is a similarity between filtered back projection and iterative reconstruction both are prospective reconstructions
what prospective recon process applies a correction filter to accentuate the edges of the attenuation info of the raw data and allows for the exact rep of the object scanned filtered back projection
what prospective recon process uses noise profiles to extract additional image clarity and suppress noise, has a very low patient dose (almost 50% less) and doesn't use the actual beam attenuation profiles from the patient like filtered back projection ASIR
what is it called when you manipulate both raw and image data after the scanning has taken place post processing
what uses only RAW DATA to create pixels that are then used to create an image image reconstruction
what uses IMAGE DATA to produce images in different planes or to produce 3D images image reformation
multiplanar reformation is uses what type of data to produce new slices in a different orientation image
what software program creates a 2D image from a 3D data set, used commonly in angiography maximum intensity projection
describe what parameters would produce good spatial resolution small slice thickness, small DFOV, large matrix, small pixels, small pitch, least amount of patient blur possible
describe what parameters would produce good contrast resolution and decrease noise higher mA/dose, larger pixel size, thicker slices, standard algorithms, avoid bone algorithms, less noise, smaller patients, smaller matrix
what is a point to point fluctuation in the CT # within a uniform material, speckled appearance of the CT image caused by insufficient photons reaching the detectors, grainy appearance noise
the factors that influence contrast resolution also influence noise
what is the ability to distinguish between similar tissues and between a structure that varies slightly in density from its surroundings contrast resolution/low contrast resolution
what is the ability to resolve small objects that are very close together and the ability to discriminate objects of varying densities a small distance apart against a uniform background spatial resolution/detail resolution

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