'Tomo' is the Greek word for
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Terms in this set (142)
GantryEntire CT systemApertureOpening/hole within the middle of the gantry4 components inside the gantryTube Detectors Slip rings Cooling unit4 components outside the gantryADC Gantry controls Positioning lasers ApertureGenerally there are 2 workstation monitors, one for ________________ and one for __________________ and _______________________Data acquisition Image recon and image displayThe power injector holds what two thingsSaline IV contrast3 fundamental steps for creating a CT imageData acquisition Image reconstruction Image display/manipulation/storage and communicationWhat is the main goal during data acquisitionProduce x-rays and have the partially attenuated beam collected by the detectorsWhat is the main goal during image reconstructionCollect data and then reconstruct it as an anatomical representation of the patientAnalog to digital converter (ADC) is involved in what fundamental step of CT image creationImage reconstructionWhat is the main goal during image displayInterpret the reconstructed data into something we can visualizeDigital to analog converter (DAC) is involved in what fundamental step of CT image creationImage displayWhat step are the tube and detectors involved in?Data acquisitionWhat step are the computer processors involved in?Image reconstructionWhat step is the workstation involved in?Data acquisition, image reconstruction, and image displayWhat does the Z-axis represent?Length of the body part being scannedWhat plane does the Y-axis represent?SagittalWhat plane does the X-axis represent?CoronalWhere do the x, y, and z planes meet?Absolute middle of the aperatureWhat is the low quality x-ray first taken to plan the rest of the procedureTopogram/scoutWhat projections is a topogram usually taken inAP and lateralNumerical data is converted into a grey scale map which is also calledWindow width and window levelWhat does window width determineRange of the greyscale - number of CT numbers represented on a specific imageFor tissues with large differences _________ window width is neededWideFor tissues with small differences ________ window width is neededNarrowWindow level sets the _______ value of the window widthMidWhat is the window level usually set atThe structure we are intentionally seeking to evaluate________ value is set for high attenuating structures like _______ with a CT number of +1000High Bone________ value is set for dense objects with low attenuation, structures like _______ with a CT number of -100 to +250Mid Soft tissue organs________ value is set for low attenuating structures like _______ with a CT number of -200 to -1000Low Air/lung parenchymaWindow width is used to select the contrast ____________ Window level is used to select the __________ of ___________Range Object of interestNeck/chest/abdomen soft tissue window width/window level350/50Brain/posterior fossa window width/window level150/30Spine/pelvic/extremities window width/window level1800/400True or False Algorithm, kernal, and convolution filter all mean the same thingTrueConvolution filter is a reconstructive property that determines the ___________ or _______________ of an image in the axial planeSharpness SmoothnessWhat are the three convolution kernels?Smooth Soft tissue SharpWhat convolution kernel is the most commonSoft tissueWhat is a CT pixel calledVoxelWhat is a voxelVolume element - 3D cube of dataIsotropicEqual on all sidesGenerally speaking, CT performs ________ imagingIsotropicWhat form of image acquisition is known as the 'step and shoot' method?Axial scanningDuring axial scanning, the time from the stop of x-ray production to the start of the next is called ___________________Interscan delay3 elements of helical scanningContinually rotating tube Constant x-ray output Constant table motionIs axial or helical scanning preferred for contrast studies?HelicalDefine pitch, what scanning is it used itTable travel during helical CTWhat is pitch equal to as an equationTable travel (mm)/gantry rotation ÷ total nominal beam width (mm)Range of typical pitch in helical scanning0.75 to 23 things pitch affects in helical scanningImage quality Dose Scan timeWhat is the average gantry tilt30° each wayGantry tilt, when used, is mostly done during what two examsHead and L-spineTypical kVp in CT120-140High kVp denotes a _________ scale of contrastLongWhat is kVpVoltage across the tube from cathode to anodeWhat does tube current represent, and what is it?mA Number of photons produced from the electrons boiled off the filament that are accelerated to strike the anodeWhat is the s in mA in CTRotation timeWhat is effective mAsTrue mAs/pitchWhat scan parameter is known as tube current modulationAECScan timeHow long it takes from the start of scanning to the endTable incrementAmount of table movement in and out of the gantry in lengthVolume coverageLength of region scannedScan delayAny delay from contrast injection to scan initiationGantry rotation speedTime to complete one 360° rotation, in seconds4 factors that affect scan timeVolume coverage Pitch Beam width + table feed Gantry revolution timeIf you increase volume coverage the scan time will become _____________LongerIf you increase table feed the scan time will become _____________ShorterIf you increase gantry rotation the scan time will become _____________ShorterAFOV stands for ___________________ which is also called ________ that stands for ____________________Acquisition field of view SFOV Scan field of viewWhat axis is most important in determining doseZ-axisWhat axis is slice thickness measured inZ-axisSmallest slice thickness size0.5mmWhat is the reconstruction incrementDistance between two consecutive reconstructed images - overlap from slice to slice3 reasons why image overlap importantVisually appealing -creates smoother image transition Ensure pathology is represented in multiple slices Ensure smaller pathologies are not missedWhat scan parameter is fixed? What one is not, and how is it determined?kVp mAs - calculated after scout based on patients buildWhat is noiseRadiation or data that does not contribute to image production5 ways noise can be reducedAlgorithms Convolution kernel Window width Abundant data CollimationWhat scanning mechanism produces volumetric scanningHelicalTrue or False Pitch is used in both axial and helical scanningFalseWhat early procedure before CT used air as contrast to image the brainPneumoencephelographyWhat two people contributed to the founding of CTGodfrey Hounsfield Allan CormackWhat decade was CT developed in?1960'sThe 1960's CT model was referred to as the _________________ model, it utilized a ________ source with a ___________ counter as the detectorLathe-bed Gamma PhotonIn _________, Hounsfield showed the first clinical images of a brain of a middle aged woman with a suspected frontal lobe tumor, using the ____________________ scanner which was located in Atkinson Morley's Hospital in London1971 Prototype EMIIn 1972 Hounsfield collaborated with Dr. ___________________, a radiologist to present Computerized Axial TomographyJames AmbroseThe EMI _______ scanner used ____ (how many) detector made of sodium iodide crystal and photomultiplier tube. The scan time was 4.5-20 minutes per ______° scan to create one slice With a matrix size of 80x_____Mk1 1 180° 80True or False The first image taken in a body prototype was in 1974 of Hounsfield himselfTrueDescribe the movement, beam, and detectors of first generation scannersMovement: Translate/rotate Beam: Pencil shaped Detectors: Single detector elementDescribe the movement, beam, and detectors of second generation scannersMovement: Translate/rotate Beam: Fan shaped Detectors: Multiple detector elementsDescribe the movement, beam, and detectors of third generation scannersMovement: Rotate/rotate Beam: Fan shaped Detectors: Multiple detector elementsWhat type of scanner is the most commonly and currently used?Third generation scannerWhat feature allows for continuous scanning in a circular motionSlip ringsDescribe the movement, beam, and detectors of fourth generation scannersMovement: Rotate/fixed Beam: Fan shaped Detectors: Multiple detector elements fixed within gantry3 limitations of fourth generation CT scannersIncreased dose due to overscanning Smaller aperture Cost of increased detectorsWhat scan beam is used in the x-axis only and what fan beam is used in the x and y-axisFan beam = x only Cone beam = x and yWhat does EBCT stand for and what is it used forElectron beam computed tomography Rapid imaging to detect calcium deposits in the heartExplain Dual Source CTThe use of 2 sets of x-ray tubes and 2 corresponding detector arrays simultaneously in a single CT gantryWhat generation scanner has a pencil shaped beamFirst generationRange of the number of rows of detectors in CT scanners, what is the most common clinically in Canada4-128 64Currently used matrix size in CT512x512Current gantry rotation timeLess than 0.2sWhere are prepatient collimators locatedBetween radiation source and patientWhere are predetector (postpatient) collimators locatedBetween patient and detectorsWhat type of collimators exist in CT and not in x-rayPredetector (postpatient) collimatorsWhat type of generator is used in CTHigh frequency, three phase transformerWhat did slip rings eliminatedLong cable that would have to unwindWhat do slip rings connectGantry to the power supply and computer system2 types of slip rings and definitionDisk - conductive and form concentric circles Cylinder - conductive and positioned along the axis of rotation to form a cylinder2 types of conductive elements in slip rings and definitionBrush wire - uses conductive wire as sliding contact - 2 brushes per ring to increase communication Composite - uses block of conductive material as sliding contactHow is power supplied in a low-voltage slip ring systemAC power > slip ring > high voltage generator > x-ray tubeHow is power supplied in a high-voltage slip ring systemAC power > high voltage generator > slip ring > x-ray tubeIn which slip ring power supply does the generator rotate with the x-ray tube?Low-voltage slip ring4 unique characteristics of a CT tubeMetal envelope Liquid bearings on stem Oil bath to dissipate heat Focusing cup strikes anode in 2 placesTrue or False The anode focal spot in CT is smaller than in x-rayFalseWhat type of filtration removes 'soft' radiation in CTInherentWhat type of filters are the most common in CTBowtieWhat type of collimator removes off focus radiationPre patientWhat type of collimator removes penumbra + scatterPost patient/predetectorWhat is an air reference detectorSmall detector placed outside of collimation to measure the intensity of the signal leaving the CT detector2 approaches as to how AEC worksUses scout image as an attenuation profile Adjusts in real time during the scanTrue or False AEC does not require a noise indexFalse3 properties that alter attenuationAtomic number Density ThicknessIn Lambert Beer Law what does I represent?Transmitted intensityIn Lambert Beer Law what does Io represent?Original intensityIn Lambert Beer Law what does x represent?Thickness of objectIn Lambert Beer Law what does e represent?Euler's constant (2.718)In Lambert Beer Law what does u represent?Linear attenuation coefficientWhy is Lambert Beer law relevent, what does it describeWhat happens to photons as they travel through various tissues based on their attenuationTrue or False Lambert Beer Law is an exponential relationshipTrue3 options that can happen to x-rays during exposureAbsorption Scatter TransmissionWhat type of scatter is more likely in CT and whyCompton Increased kVpWhere is the high voltage transformer located in a high voltage slip ring?Outside of the gantry