CT Registry Flashcards
Computed Tomography uses what
X-Rays to image individual slices through the body
X-Rays are directed
Into a localized section of the patient
How is an image seen (simple)
Detected signals are constructed into an image
CT system console controls what
Information about the pt
specific imaging parameters
post-processing techniques
filming and arching instructions
CT Console information goes…
To the Host computer, translated into systems machine language then to scan controller.
Scan Controller controls what
Responsible for timing and operation of pt table, gantry and high voltage generator
How is information from the scan controller sent
Electronic signals are converted into analog (continuous) waveform. DAS converter accomplishes this.
What does the Gantry contain
CT X-Ray tube
Detectors
The technique that allows the user to select the range of pixel values used in a 3D ct reformation is termed
Thresholding
A voxel’s dimension may be decreased by
Decreasing the section width
What may cause abnormal findings and will reduce the density of the liver?
Fatty Infiltrate
Patients whose posterior descending artery branches from the right coronary artery, and whose left posterior ventricle branches arise from the left circumflex artery, are said to be
Codominant
What does it mean to be Codominant
7% of the population is said to be codominant, meaning that the posterior descending artery (PDA) is supplied by the right coronary artery (RCA) and the left posterior ventricular branches arise from the left circumflex artery (LCA)
The articulation between the distal tibia and the fibula is called the
Syndesmoisis
For MDCT identified areas of calcium must demonstrate relative attenuation values greater than
+130 HU
1st generation scanner produced what type of x-ray beam:
Thin “pencil beam”
How many detectors did a 1st generation ct use
One detector
How did the tube/detectors assembly work/move in a 1st generation scanner
Across the patient then rotated by 1 degree
Total scan time for 1st generation ct
5 mins per image
Anatomy scanned on 1st generation
Head
2nd generation scanners produced what type of x-ray beam
Fan Beam
How many detectors did a 2nd generation use
Multiple @30, in a straight line called an array
How did the tube/detector assembly on a 2nd generation scanner work/move
Across the patient, then rotated by 5 degrees
Total scan time on a 2nd generation scanner
20 seconds per image
3rd generation scanners produce what type of x-ray beam
Fan Beam
How many detectors will a 3rd generation scanner have
Multiple detectors along an arc
How does the tube detector assembly move/work on a 3rd generation
The tube/detector assembly rotates around the patient.
Total scan time on a 3rd generation
Faster than 1 second per image
Most scanners today are based on what generation of CT scanner
3rd
4th generation scanners produces what type of x-ray bea
Fan Beam
How many detectors will a 4th generation have
Multiple detectors encircle the patient and do not rotate
How does the tube/detector assembly move/work on a 4th generation
Only the tube rotates around the patient.
Total scan time on a 4th generation
Faster than 1 second per image
The Slip Ring transfers the following information between stationary components and the rotating gantry
Electrical power
Scanning instructions
detected signals
Multirow detectors collect information from _____ and how does this affect the scanned anatomy
Multiple anatomical slices in each rotation.
Anatomy can be scanned faster without increasing the slice thickness or varying the pitch
MDCT
Multi-row Detector Scanners
MSCT
Multi-array Scanner
MDCT Systems use what type of x-ray beam
Cone Beam
Describe an electron beam CT scanner and it’s use
Alternative design that has no x-ray tube
Very fast scan times making it suited for cardiac and coronary artery imaging.
What is fusion imaging and what is most commonly associated with it
Comparison of two imaging modalities yielding co-registered images.
PET/CT scanners
What does PET stand for
Positron Emission Tomography
PET images are sensitive to changes in…
Metabolism associated with malignant tissues
What is the value of overlaying PET images with High-Resolution CT images
Best to associate a change in metabolism with a specific structure.
How is cone beam CT associated with oncology
Cone beam CT is being used in the oncology department in order to verify patient positioning prior to receiving radiation therapy.
CT Colonography images are best displayed in what window settings:
“lung-type” -400L/1600W
____ is a term that refers to an excessive amount of nitrogenous materials in the blood and is a symptom of renal failure.
Azotemia
AKA uremia Azotemia
How do you determine the linear dimension of each pixel?
DFOV/Matrix size
*convert cm-mm /add zero to end of cm
What measuring unit is used to quantify effective dose?
Sieverts
What does Effective Dose Mean
ED approximates the relative risk from exposure to ionizing radiation and is based on the radiosensitivity of a given tissue type.
Phantom measurement of the uniformity of a CT system is performed primarily to assess the negative effets of
Beam Hardening
As low-energy x-ray photons are absorbed when the beam passes through the patient, the average photon energy of the beam increases along the path and may result in a loss of system uniformity. This is known as
Beam Hardening
The type of hemorrhage that occurs between the skull and outer layer of the dura in traumatic brain injury is referred to as
Epidural Hematoma
The type of hemorrhage that occurs between the dura matter and the inner layer of meninges known as the arachnoid is called
Subdural Hematoma
Increased section width or increased table speed will play a roll in increasing
Pitch
An increase in Pitch is the result of
An increase in section width or increase in table speed
The process of scanning a phantom device of known density to improve the accuracy of CT attenuation measurement maybe referred to as
Calibration
What type of artifact manifests as a streaking effect at areas of extremely-high-density interfaces
Edge Gradient
The soft center of each inter-vertebral disc is called the
Nucleus Pulposus
How do you calculate DFOV (display field of view)
Pixel dimension X matrix size
ex: 320 matrix, 0.75 mm x 0.75mm pixel dimension
320X.75=240/24cm
A high-osmolar contrast material has an average osmolality of
1000-2400 mOsm/kg Water
Operator’s console
Key point of interaction between the technologist and the imaging system
Host computer
Primary link between technologist and the other components of the imaging system
Gantry houses
X-Ray tube
Detectors
Slip Rings
High voltage generator
Patient table
Controlled by software according to tech instruction.
Patient coordinates “Axis”
X: Left to Right
Y: Anterior to Posterior
Z: Head to Feet
Tungsten Atomic Number
High 74
The average CT value for blood is @
+45
Pulmonary nodes assumed to be benign have an average density within what range?
+164 and higher
The normal range for the International Normalized Ratio (INR) for Prothrombin Time (PT) results in
-0.8- -1.2
INR stand for and is what
International Normalized Ratio
INR compares a patients PT with a control sample for more accurate results.
An increase in Sample Frequency results in
an Increase in Spatial Resolution
Describe the relationship between Slice Sensitivity Profile (SSP) and dose profile
Dose profile is always HIGHER than SSP
High resolution CT examinations of the temporal bones and internal auditory canal should include
Thin sections (1-2mm) Small targeted DFOC (less than 10cm) High Resolution algorithm (kernal) for reconstruction
A good display field of view (DFOV) for a thorasic spine would be:
15 cm
Calculate beam pitch
Total # of sections (detectors) multiplied by the detector dimension, then divide the table movement by answer above.
What measuring units Quantify absorbed dose?
Greys
*absorbing x-rays give shades of gay (Greys)
The approximate inherent filtration of the CT x-ray amounts to an aluminum equivalent of
3.0mm
What term describes a condition in which cerebral ischemia is caused by systemic hypertention
Vasovagal reaction
What phase of renal contrast enhancement provides maximum sensitivity for parenchymal lesions?
Nephrographic
70-90 seconds after injection
Multiplanar reformations (MPR) images along the long axix of the optic nerve would be best described by which of the the following anatomic planes?
Oblique Sagittal
The ability of CT system to reduce involuntary motion artifacts and provide CT images free of motion artifact is determined by which of the the following components of image quality
Temporal resolution
Temporal resolution=stop motion/no blurring
What mathematical functions may be used to quantify the spatial resolution of a CT scanner
PSF (Point Spread Function)
MTF (Modulation Transfer Function)
LSP (Line Spread Function)
In multislice CT (MSCT) the beam of pitch is equal to the table feed per rotation divided by the
Total collimation
A decrease in matrix size will
Decrease Noise
The Iliac artery bifurcates at
L5-S1
Pathway of blood
- From Superior & Inferior Vena Cava’s (and coronary sinus) to-
- Right Atrium, through the tricuspid valve to-
- Right Ventricle, through the Pulmonary Semilunar Valve to-
- Pulmonary Trunk, Rt and Lt pulmonary Arteries to lungs, from lungs to-
- Heart, through Plumonary Veins to-
- Left Atrium, through bicuspid (mitral) valve to-
- Left Ventricle, through aortic semilunar valve to-
- Ascending aorta
Collimation restricts x-rays to only the selected cross-sectional region. How does this affect the pt.
It minimized the dose to the pt and reduces scatter.
Pre-patient collimation is a factor indetermining the slice thickness in _____ dectector CT, but NOT in _____ detector CT
Single-row
Multi-detector
In order for an x-ray photon to generate a signal, it must
- enter the detector
- collide with a detector atom
- produce a measurable event
What type of detectors are the most prevalent type used on today;s CT scanners?
Solid State
What happens when a photon strikes a solid state material/detector?
It emits a flash of light which is converted into an electrical impulse by a photodiode.
How do you calculate acquired slice thickness on a MDCT scanner?
The thickness of the x-ray beam is divided by the total number of slices acquired in a single rotation.
What is the primary function of the array processor?
Reconstruction of the projected attenuation raw data into CT images
In radiology, a network refers to
A number of interconnected digital devices that need to share information
How many bits are in a byte?
8
Which stage following renal contrast enhancement provides maximum sensitivity for parenchymal lesions?
Nephrographic (70-90 minutes after injection)
*PN (like PM-time of day)
The ability of an object to attenuate the x-ray beam is assigned a value known as the
Linear attenuation coefficient
An increase in detector pitch does what
Raises the rate at which the patient moves through the gantry during data acquisition, thus lowering patient dose.
In CT a decrease in KVp does what to patient dose?
Decreases patient dose, (opposite of x-ray)
Ischemic brain tissue is identified as an infarct core when cerebral blood volume (CBV) falls below:
2.5 ml/100g
What terms are commonly used to describe a CT scanners ability to differentiate objects with similar linear attenuation coefficients?
Sensitivity
Contrast Resolution
Which of the following components of CT image quality may be controlled by the technologist:
- Spatial Resolution
- Contrast Resolution
- Noise
ALL OF THEM
Spatial resolution is affected by what geometrical factors?
Focal Spot Size
Slice Thickness
Contrast Resolution may be altered by
Size Thickness
Algorithm Selection
Noise
The Basilary artery and Middle (Rt & Lt) cerebral arteries are NOT part of what part of the brain?
Circle of Willis
Phantom measurement of the uniformity of a CT system is performed primarily to assess the negative effects of
Beam Hardening
The best method of reducing the risk of contrast induces rephrocity (CIN) is
Adequate patient hydration
What type of image reconstruction was used in the first prototype CT scanner
Iterative technique
The degenerative pathologic process of the spine known as spondyloysis involves a defect in the
Pars Interarticularis
The process of scanning a phantom device of known density to improve the accuracy of CT attenuation measurement may be referred to as
Calibration
The ability of a CT scanner to image a small high-density object is controlled by the _____ of the scanner
Spatial Resolution
Areas of a CT image containing abrupt changes in tissue density are electronically represented by
High Spatial Frequencies
A grid of pixels comprise a
Matrix
The width of a CT window controls
The range of pixel values
When one is choosing a window to display a CT image, the width defines
The range of CT numbers (pixels) to be displayed
In patients who are right dominant, the posterior descending artery branches from the
Right Coronary Artery
The full width at half maximum (FWHM) of a slice sensitivity profile diagram indicates the
Effective Section Width
The quantity of radiation dose received by the pt from a series of CT scans is referred to as
MSAD (Multi Slice Average Dose)
The calculation of the average cumulative dose to each section within an acquisition of Multiple Sections is termed the
MSAD (Multi Slice Average Dose)
The approximate radiation dose measured during a scan of a 100-min pencil ionization chamber is the
CTDI
Technological factors that exhibit an effect upon Longitudinal Spatial Resoultion
- Detector Pitch
- Interpolation algorithm
Glimoa tumors are found in the
Brain
A decrease in apperature size will increase
Noise
PET system absorbs what type of radiation
Annihilation Photons
Agaston Scores for MDCT cardiac examination
1-10
Min
Agaston Scores for MDCT cardiac examination
11-100
Mild
Agaston Scores for MDCT cardiac examination
101-400
Moderate
Agaston Scores for MDCT cardiac examination
>400
Extensive
