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CT registry review 1
CT
| Question | Answer |
|---|---|
| What are 2 rights of the patient? | 1. Pt has the right to considerate & respectful care. 2. Pt has the right to refuse medical treatment. |
| What are the instructions given to the patient before starting any CT exam? | 1. Describe the exam to be performed: area of body, ect. 2. Explain the process of contrast administration. 3. Give any necessary breathing instructions clearly & precisely. |
| Beam Hardening | The phenomenon whereby low-energy phontons are absorbed as the x-ray beam passes through an object, resultin in an increase in the average photon energy of the beam. |
| Beam Pitch | The ratio of table feed per gantry rotation to the total collimation used during acquisition with a multislice CT (MSCT) system. |
| Beam Width | The dimension of the primary beam in the longitudinal or z-axis as controlled by the pre-patient collimator. |
| Binning | The process of electronically combining signal from adjacent detector elements to produce a reconstructed CT image that is thicker than the individual width. |
| Bit Depth | The number of information bits contained within each pixel. |
| Back-projection | The mathematical process of CT image reconstruction whereby ray sum data are projected back onto a matrix. |
| Blood urea nitrogen (BUN) | A measurement of renal function, determined as the amount of nitrogen in the blood in the form of the waste product urea. The normal range is 7-25 mg/dL |
| Bow-tie filter | A type of filter added to the CT x-ray tube to compensate for the cylindrical shape of most body parts. The filter is thicker at the ends & helps shape the beam to reduce patient radiation exposure. |
| Cardiac cycle | The series of blood flow-related events that occur from the beginning of one heartbeat to that of the next. |
| Cerebral blood flow (CBF) | A common measurement during CT perfusion studies of the brain. CBF is the quantity of blood (ML) that moves through 100g of brain tissue each minute. Normal range in gray matter is 50-60 ML/100g/min |
| Cerebral perfusion | The level of blood flow throughout brain tissue. |
| Constant mAs | The product of milliamperage (mA) and scan time (seconds) utilized for a CT acquisition. |
| Contiguous images | CT images acquired with equal section thickness and reconstruction intervals. |
| Contrast-induced nephrotoxity (CIN) | A substantial decline in renal function that can occur after a patient receives IV contrast material. It is usually signified by a marked increase in serum creatinine over a baseline measurement obtained prior to contrast agent administration. |
| CT Bronchography | Specialized MSCT examination of the tracheobronchial tree consisting of MPR and volume rendered 3D images reconstructed from thin, overlapping MDCT axial images through the airways. |
| CT Arthrography | CT evaluation of a joint after the intra-articular injection of iodinated contrast material. |
| CT Enterography | Specialized CT evaluation of the small bowel after the oral administration of low density (0.1%) barium. |
| CT Fluoroscopy | Continuous real-time CT imaging used predominantly for CT-guided interventional procedures. |
| CT Myelography | CT evaluation of the spinal cord and nerve roots after the intrathecal administration of iodinated contrast material. |
| CT Number | Relative value assigned to each pixel to quantify the attenuation occurring in each voxel in comparison with the attenuation of water. The calculated CT number for a given pixel is given in Hounsfield unit (HU). May also be referred to as pixel value. |
| CT Runoff | The CT angiographic assessment of the peripheral arterial tree from the renal arteries through the lower extremities. |
| CT Simulation | The process of obtaining anatomic information with CT imaging that is used to calculate the beam arrangement for radiotherapy. |
| CT Colonography | Specialized CT evaluation of the large intestine used primarily for colon cancer screening.The large intestine is extended & scanned with thin-section CT. 2D & 3D models are constructed, including virtual endoscopic fly-through views. |
| CT Cystography | Specialized CT examination of the bladder whereby iodinated contrast material is administered directly under gravity into the bladder via Foley catheter. |
| CT Dose index (CTDI) | An approximate measure of the radiation dose received in a single CT section or slice. |
| CT Enteroclysis | Specialized CT evaluation of the small bowel whereby enteral contrast material is administered directly into the duodenum through a nasogastric catheter placed under fluoroscopic guidance. |
| Convolution | Mathematical filtration used by the CT system to remove blurring artifact during the back-projection method of image reconstruction. |
| Corticomedullary phase | A late arterial phase of renal enhancement beginning 30-40 seconds after the initiation of contrast agent administration. Optimal enhancement of the renal cortex & renal veins occurs during this period. |
| Creatinine | A waste product of metabolism found in the bloodstream & measured as an indicator of renal function. Normal range: .5-1.5 mg/dL |
| 180-degree linear interpolation (180LI) | Type of algorithm used for MSCT image reconstruction in which data acquired from a shorter distance (180 degrees) away from the reconstructed slice location are interpolated. |
| 360-degree linear interpolation (360LI) | Type of algorithm used for MSCT image reconstruction in which two sets of projection data acquired 360 degrees apart are used to form an image at a precise z-axis location. |
| Absorbed dose | The amount of x-ray energy absorbed in a unit of mass. It is measured in grays (Gy). |
| Absorption efficiency | The ability of an individual CT detector to absorb & measure the transmitted x-ray intensity incident upon it. Primarily controlled by the characteristics & physical makeup of the detector material. |
| Adaptive array | The type of MSCT detector array configured with the thinnest detectors at the center, surrounded by detectors of incrementally increasing widths along the a-axis. |
| Scout Image | Digital survey radiograph acquired by the CT system for the purpose of prescribing the cross-sectional acquisition. Similar to a conventional radiograph. |
| What mathematical technique is used exclusively for image reconstruction with spiral CT scanners? | Interpolation |
| ALARA | The principle that radiation exposure should be kept as low as resonably achievable, economic & social factors being taken into account. |
| Algorithm | Computer adapted mathematical calculation applied to raw data during the process of image reconstruction. Computer compatible equation. |
| Aliasing Effect | Artifacts that appear on the CT image as fine lines. They occur when too few samples are acquired. Also called sampling artifacts. |
| Aluminum (Al) | Metal most frequently selected as x-ray beam filter material because it effectively removes low-energy x-rays. |
| Ampere (A) | The SI unit of electric charge. 1A=1 c/s |
| Analog signal | Continuous display of energy intensity, or radiation, as opposed to the discrete display of a digital signal. |
| Anode | Positive side of x-ray tube, containing the target. |
| Anthropomorphic | Human Characteristics. |
| Contrast resolution | The ability of a CT system to detect an object with a small difference in linear attenuation coefficient from the surrounding tissue. May also be referred to as low-contrast detectability or sensitivity. |
| Attenuation | The progressive reduction of the intensity of the x-ray beam, as it passes through the patient's tissues. |
| Absorbed Dose | Energy transferred from ionizing radiation per unit mass of irradiated material. Expressed in rad (100 erg/g) or gray (1J/kg). |
| Absorber | Any material that absorbs or reduces the intensity of radiation. |
| Absorption | Transfer of energy from radiation to matter. Removal of x-rays from a beam via the photoelectric effect. |
| Acute | Beginning suddenly & running a short but rather severe course. |
| Acute effects | See early effects. |
| Added Filtration | Aluminum (or its equivalent) of appropriate thickness positioned outside an x-ray tube & in the primary beam. |
| Aluminum equivalent | Thickness of a material resulting in the same attenuation as aluminum. |
| ACMP | American College of Medical Physicists |
| What is the ACMP | Professional society of medical physicists. |
| AAPM | American Association of Physicists in Medicine. |
| What is the AAPM | Scientific society of medical physicists. |
| American College of Radiology (ACR) | Professional society of radiologist & medical physicists. |
| American Society of Radiologic Technologists (ASRT) | Scientific & professional society of radiographers. |
| Array Processor | A specialized component of the CT computer system. It is capable of performing the massive calculations req'd for CT image reconstruction. |
| Lipoma | A benign mass consisting of fat cells. |
| Angiomyolipoma | A common benign mass found in the kidneys, consists of muscle cells, blood vessels & fat. |
| What is the average CT value range for fat? | -50 to -100 Hounsfield units |
| Absorption Efficiency | The ability of an individual CT detector to absorb & measure the transmitted x-ray intensity incident upon it. Primarily controlled by the characteristics & physical makeup of the detector material. |
| Interpolation | The mathematical technique allowing the reconstruction of motion free images from helically acquired CT data. |
| Interpolation | Is the mathematical process whereby data from tube rotations just above & just below a given slice position are used for image reconstruction. |
| The peritoneal cavity is formed by the membranous sac called the ___________. | Peritoneum |
| What does the peritoneal cavity contain? | Stomach, liver, gallbladder, spleen, ovaries, transverse colon, & most of the small bowel. |
| CT scan of the pelvis should include what? | From the iliac crests to the pubic symphysis. |
| What is the recommended scan field of view (SFOV) for a CT exam of the CSP? | 50.0 cm |
| In comparison w/ the surrounding soft tissues, the thyroid gland is ___________. | Hyperdense on the CT. Because it naturally contains iodine. This density increases further w/ administration of an iodinated contrast agent. |
| The gantry contains some of the most important components of the scanner including what? | 1. CT x-ray tube. 2. Detectors |
| What type of information can be entered @ the CT console? | 1. Imaging parameters 2. Post processing techniques 3. Filming & archiving instructions |
| The scan controller is responsible for the timing & operation of what? | 1. Patient table 2. Gantry 3. High voltage generator |
| What does DAC stand for? | Digital-to-Analog Convertor |
| What is the easiest way to increase the # of photons? | Increase the tube current or the scan time. |
| When should increasing the dose to the patient be considered? | Only when the result of not doing so would otherwise be a non-diagnostic study. |
| Patient Dose | The dose is the amount of ionizing radiation absorbed by the patient per unit mass. |
| There is a tradeoff between _______ the image quality & ________ the patient dose. | Maximizing Minimizing |
| Noise | When a CT image looks grainy or speckled. |
| What made helical imaging possible? | Continuous rotation scanners. |
| What are 3 functions of PACS? | 1. Long term data storage 2. Digital distribution of images 3. Image display for the radiologist |
| Image reconstruction is handled in the _______ ________. | Array Processor |
| Multi-row detector CT scanners: | 1. The size of the detector arrays along the z-direction may be different. 2. The attenuation information from adjacent detector arrays may be added together to generate thicker slices. 3. All of the detector arrays may or may not be used. |
| What does mA determine? | Quantity of x-ray photons. |
| State 4 items that are true regarding the collection of CT data. | 1. Short scan times are more desirable. 2. The reconstruction process used to create the image occurs in the array processor. 3. To collect the complete set of CT data, x-rays must be passed through the body at many different angles. |
| 4. The detectors measure x-rays which completely penetrate the patient. | |
| What components are normally located in the gantry of a modern CT systems. | 1. x-ray tube 2. detectors 3. collimators (pre-patient & post-patient) |
| Where does the analog signal go to after it leaves the amplifier component? | The sample-and-hold component. (S/H) |
| On an ECG of the complete cardiac cycle, at which portion of the R-R interval is the heart muscle in diastole? | 55% - 75% |
| Vacuum Phenomenon | The accumulation of gas within a degenerating intervertebral disk. |
| How are spiral/helical CT exams obtained? | With the scanner continuously acquiring data as the patient travels thru the gantry. The data acquired are volumetric, containing all of the attenuation info. for a given area of anatomy. |
| When compared with conventional radiography, CT produces dianostic images with improved what? | Low contrast resolution. |
| Complete cardiac diastole correspond to which portion of the cardiac cycle on a electrocardiogram (ECG)? | T wave |
| During CT arthrography, iodinated contrast media is injected directly into what? | Joint space |
| Leiomyoma | A benign mass of smooth muscle. It commonly occurs in the uterus & is readily identified on CT exam as a bulky, nonspecific uterine enlargement. |
| The section thickness of a CT scan directly affects what? | The detail & spatial resolution of the image. Narrow section widths result in greater detail for imaging of small anatomic parts such as the sinuses. |
| What is the section thickness for paranasal sinuses? | 3 mm |
| Overbeaming | Expansion of the primary beam in an MSCT system to ensure that all detectors of the array are exposed to x-rays of equal intensity. |
| Name 3 common sites for IV injection of iodinated contrast. | 1. Cephalic vein 2. Antecubital vein 3. Basilic vein |
| An intrathecal injection prior to a CT exam of the LSP places iodinated contrast material directly into the ________ ______. | Subarachnoid space |
| Automatic tube current modulation (ATCM) is employed by an MDCT system for what purpose? | Reducing patient radiation dose. |
| High resolution computed tomography (HRCT) is most commonly used for what? | Lungs |
| Retrospective ECG gating | Maneuver that may be used to remove unwanted pulsation artifacts from cardiac motion during a CTA of the chest for pulmonary embolism. |
| Name 4 types of contrast media. | 1. Intravascular Radiopaque 2. External Radiopaque 3. Negative contrast agents 4. Neutral contrast agent |
| The adult spinal cord ends at what level of the lumbar vertebra? | L1-L2 At this level it tapers to a point known as the conus medullaris. |
| How are 3D studies best performed? | With the use of narrow sections acquired with no spacing or preferably an overlap. A detail (bone) algorithm is used for optimal demonstration of bony structures. |
| Adaptive array | the type of MSCT detector array configured with the thinnest detectors at the center, surrounded by detectors of incrementally increasing widths along the z-axis. |
| Advanced single slice rebinning (ASSR) algorithm | Cone beam correction algorithm utilized to overcome potential attenuation calculation errors from the divergent beam of MSCT systems. |
| Afterglow | The tendency of a scintillation type CT detector to continue to glow in response to x-radiation after the exposure source has been terminated. |
| Agatston score | Quantification of the volume & density of calcium within the coronary arteries. As calculated during a CT coronary artery calcification (CAG) examination, the Agatson score is used to indicate a patients risk of suffering a cardiac event. |
| Display field of view (DFOV) | The diameter of the acquired attenuation data displayed across the image matrix. May also be referred to as the zoom factor or target view. |
| Scan field of view (SFOV) | A parameter that controls the diameter of the circular data acquisition field within the CT gantry as determined by the # of activated detectors along the x-y axis. May be referred to as calibration field. |
| ALARA | Acronym for as low as reasonably achievable, the cardinal principle of radiation dose reduction for all radiological procedures, including CT. |
| Algorithm | Mathematical filter applied to raw data during CT image reconstruction to remove blurring artifact inherent to back projection. May also be referred to as a kernel. |
| Aliasing | A form of streak artifact caused by an insufficient # of views (data samples) obtained during data acquisition. |
| Analog-to-digital converter (ADC) | Component of the data acquisition system (DAS) responsible for converting the electronic signal emitted by the CT detectors into digital form. |
| Archival | The storage of CT data in either hard(film) or soft (digital) form. |
| Array Processor (AP) | Component of the CT computer system responsible for receiving raw scan data, performing all of the major processing of the CT image & returning the reconstructed image to the storage memory of the host computer. |
| 1st Generation scanners | - pencil beam - single detector - the tube/detector assembly moved across the patient, then rotated by 1 degree - total scan time about 5 min per image - used for head study - translate-rotate motion |
| 2nd Generation scanners | - fan beam - multiple detectors in a straight line - the tube/detector assembly moved across the patient, then rotated by 5 degrees - total scan time about 20 secs per image - translate-rotate motion |
| 3rd Generation scanners | - fan beam - several hundred detectors- curvilinear detector array - 360 degree rotate-rotate motion. Both the x-ray source & the detector array rotate about the same axis. |
| 4th Generation scanners | *fan beam *multiple detectors encircle the patient and do not rotate around the patient * Only the tube rotates around the patient * Total scan time of 1 second per image or faster |
| What are the indications for CT exmas of the head? | Evaluation of trauma, stroke, headache, tumors, endocrine disease, inflammatory disease & congenital problems. |
| The primary goal of CT image reconstruction is to spatially distribute the attenuation data recorded by the _______ _______. | Detector Array |
| The International Normalized Ratio (INR) is calculated to standardize which laboratory value? | Prothrombin time (PT) |
| Surgical Asepsis | Infection control techniques required at the site of IV injection of iodinated contrast media. |
| What is the primary goal of multiphasic CT evaluation of a pancreatic mass is what? | The determination of tumor respectively. |
| What are the factors that determine the potential for surgical removal of a pancreatic tumor? | 1. vascular involvement of the mass 2. local tumor spread 3. metastases |
| Which technology do multirow detector scanners employ? | 3rd Generation |
| What is scatter radiation caused by? | Deflections from the original trajectory of an x-ray photon through the patient. |
| The patient table may move _________ during the scan. | continuously |
| Most of the commands from the technologist are received by the what? | Operator's console |
| Name 3 things the operator's console may include. | 1. monitor 2. keyboard 3. graphic input device |
| What does the tube interscan delay time refer to? | The time between the end of one scan and the start of the next scan during which the tube will cool. |
| Increased ___ will increase the likelihood that a given x-ray will penetrate a material. | kV |
| Increasing the ____ or exposure time will increase the total number of photons, but will not increase the likelihood that each of those photons will penetrate the material. | mA |
| How is collimation accomplished? | By physically blocking x-rays. |
| Scatter radiation is caused by what? | Deflections from the original trajectory of an x-ray photon through the patient. |
| Multirow detector scanners employ what type of technology? | 3rd generation |
| In order for an x-ray photon to be measured it must what? | 1. enter the detector chamber 2. be absorbed by the detector material 3. be converted to a measurable event. |
| The operator's console may include what 3 things? | 1. monitor 2. keyboard 3. graphic input device |
| Most of the commands from the technologist are received by the: | Operator's console |
| The following are true regarding CT systems: | 1. The gantry can tilt to an angle of approx. 30 degree 2. The patient table, gantry tilt mechanism & rotating gantry assembly all incorporate moving parts. 3. They can generate a straight coronal or sagittal image. |
| What does the Kv control? | 1. the voltage potential between the tube cathode & anode while mA ultimately controls the filament current & thus the temp. of the cathode filament. 2. the energy level of the x-ray photons & mA controls the # of x-ray photons emitted from the tube. |
| What are some of the parameters that we directly control that affect spatial resolution? | * slice thickness * display FOV * image matrix * the reconstruction filter |
| The full width at half maximum (FWHM) of a CT scanner is used to describe what? | spatial resolution |
| Spatial resolution | The ability of a CT imaging system to display fine details separately. Given in units of line pairs per centimeter. |
| Which CT scanner designs use an x-ray tube? | 1st - 4th generation CT PET/CT MDCT |
| Which CT scanner design does not use an x-ray tube? | Electron beam CT |
| What is the main purpose of the detector? | Capture x-ray photons & convert them to a measurable signal. |
| Transverse slices are always acquired, but studies of the internal auditory canals, pituitary, orbits, sinuses & facial bones also require what? | Coronal slices |
| ________ scanner design was the 1st to acquire 4 slices in a single rotation. | Multi-row Detector |
| Tungsten is used as the target material on the tube's anode because it has a ________ atomic # & a _______melting point. | high, high |
| What does tube interscan delay time refer to? | The time between the end of one scan and the start of the next scan during which the tube will cool. |
| What factors affect the dimensions of a voxel? | 1. slice thickness 2. matrix size 3. DFOV |
| What are the 4 influences on parameter selection? | 1. contrast resolution 2. spacial resolution 3. image noise 4. patient dose |
| Bremsstrahlung radiation includes which type of electron activity? | 1. collision between an incoming electron & the nucleus of the target atom. 2. slowing down of an incoming electron due to the effect of passing close to the positive charge of the nucleus of the target atom. |
| Why are x-rays produced whenever fast moving electrons collide with any form of matter? | The electron loses kinetic energy which is converted into the emission of an x-ray photon. |
| Ray Sum | The measurement of transmitted radiation made by an individual detector. |
| The information included during the 3D reconstruction of a CT scan is controlled by the _________ __________. | Threshold setting |
| Diastole | Refers to the relaxation of heart muscle. |
| High-osmolar contrast media (HOCM) | Are ionic agents that dissociate into charged particles (ions) in solution. |
| Ionic contrast media | Are salts consisting of sodium and/or meglumine. |
| Orthogonal | Imaging planes that are perpendicular to each other. |
| Segmenting the data acquisition process into seperate components of smaller rotation angles may improve _______ ________. | Temporal resolution |
| _______ _______ artifacts are unique to MSCT systems. | Cone beam |
| What are 2 analytic methods of CT image reconstruction? | 1. filtered back-projection 2. fourier transform method |
| Why are the techniques called analytic? | Because they utilize precise formulas for image reconstruction. |
| The average photon energy of the CT x-ray beam can be increased by increasing what? | Filtration |
| Photodiode | Solid state device used to record the light flashes given off by a scintillation crystal. |
| Automatic tube current modulation (ATCM) | Software used in current MDCT systems to control patient radiation dose. |
| Uniform matrix array | The type of MSCT detector array that utilizes multiple detectors in the longitudinal direction, each of the same length. |
| High resolution CT | Is a specialized technique using narrow section widths & a high resolution algorithm for image reconstruction. It is used to maximize detail of high spatial frequency tissue, such as the lungs & bony structures. |
| Simple cysts of the kidney have average attenuation values in the range of what? | 0 to +20 Hounsfield units |
| The abdominal aorta bifurcates at the level of _______. | L4 |
| Contrast enhancement of vasulature greatly aids in the diagnosis of many disorders including.... | 1. aneurysm 2. thrombus 3. stenosis |
| What is effective dose? | The quantity of absorbed radiation dose based on the radiosensitivity of a particular tissue type. |
| What is the normal rate for diastolic blood pressure in adults? | 60-90 mm Hg |
| What is diastolic pressure? | The measurement of blood pressure at its lowest point, in between contractions of the heart. |
| What is complete cardiac diastole? | The period of atrial & venticular relaxation after heart contraction. |
| What wave of an ECG corresponds to cardiac diastole? | T wave |
| Name general signs & symptoms that a patient is going into shock. | 1. rapid breathing 2. tachycardia 3. hypotension 4. weak pulse 5. pallor 6. cyanosis 7. cold clammy skin |
| __________ is a parenteral route of meication administration. | Intramuscular |
| Name 3 methods that may be employed to reduce radiation dose to pediatric CT patient's. | 1. reduce mA 2. limit phases of acquisition 3. increase pitch |
| Radiation exposure & its potentially harmful effects have a relationship that is termed __________. | Stochastic |
| What type of isolation technique protects against infection transmitted through fecal material? | Enteric precautions |
| Mild reactions to iodinated contrast media include: | 1. nausea/vomitting 2. mild urticaria (hives) 3. pronounced sensation of warmth and/or flushing 4. altered taste 5. sweat/chills 5. nasal stuffiness/sneezing 6. anxiety |
| Moderate reactions to iodinated contrast agents include: | 1. mild bronchospasm 2. moderate to severe urticaria (hives) 3. vasovagal response 4. tachycardia from hypotension |
| Severe reactions to iodinated contrast include: | 1. profound hypotention 2. laryngeal edema 3. severe bronchospasm 4. pulmonary edema 5. cardiac arrhythmia 6. seizure 7. cardio- pulmanary arrest 8. death |
| A patient in shock may exhibit what symptoms? | 1. tachycardia 2. rapid, shallow breathing 3. cyanosis |
| What is SOLU-CORTEF? | A brand name for hydrocortisone, which is a type of corticosteroid. May be used during the treatment of anaphylactoid reacations to iodinated contrast materials. |
| What technical factors has a direct effect on patient dose? | With no consideration of image quality, reductions in mA and/or scan time(seconds). |
| Name the non-ionic contrast media. | 1. iopamidol (ISOVUE) 2. iohexol (omnipaque) 3. iopromide (ultravist) |
| What is dyspnea? | Used to define the condition of difficult breathing. |
| What factors may affect a patient's calculated glomerular rate (GFR)? | 1. age 2. sex 3. race |
| What intravenous contrast agent administration method provides the greatest overall plasma iodine concentration? | Bolus technique |
| What device is used to measure the patient dose from a CT exam? | Ionization chamber |
| What is implied consent? | Describes the situation in which an assumption is made that an unconscious or otherwise physically unable patient consents to medical treatment. |
| What system component is responsible for converting the digital signal into analog form? | D to A converter |
| The reduction in intensity of an x-ray beam as it interacts with matter is termed what? | Attenuation |
| A CT image is formed in part by projecting back all of the attenuation values recorded during data acquistion onto what? | Matrix |
| CT Urogram | A comprehensive, multi-phasic CT evaluation of the urinary tract. Consists primarily of pre-contrast, post-contrast & delayed CT acquisitions through the kidneys, ureters, and bladder. It may also be commonly referred to as a CT-IVP. |
| Data acquisition system (DAS) | The electronic components of a CT system responsible for measuring the transmitted x-radiation absorbed by the detectors. |
| Data channel | Pathaway of data transmission from the detectors to the computerized components of the system's data acquisition system. The number of data channels of a CT system determines the maximum number of sections that may be acquired with each gantry rotation. |
| Arterial phase | Period of peak arterial enhancement following the bolus IV administration of iodinated contrast material. For ex, the hepatic arterial phase occurs approx. 25-35 seconds after the initiation of contrast agent administration. |
| Artifact | A form of noise on the CT image resulting from errors during the measurement of transmitted radiationby the detectors. |
| Attenuation coefficient | The value assigned to an object quantifying its ability to attenuate an x-ray beam. |
| Automatic tube current modulation (ATCM) | CT system software used to adjust the mA throughout an acquisition to reduce patient radation dose to a minimum. |
| Cupping artifact | An error occurring in the superior portion of the skull, where dense bone averages with the low-attenuating brain tissue. This partial volume artifact may result in abnormally dense-appearing brain parenchyma. |
| CT console | Where instructional commands are entered by technologist. |
| CT host computer | Translate each command as it is entered into the systems machine language. |
| CT scan controller | Responsible for the timing & operation of the table, gantry & high voltage generator. |
| DAC | Responsible for converting the digital signal into an analog form. |
| High voltage generator | Produces high voltage potential that exists between cathode & anode. |
| Amplifier | Amplify's signal strength sent in analog form. |
| Sample & hold (S/H) | Signal is sampled here 1st. |
| Analog to digital converter (ADC) | Signal is digitized by ADC. Then stored temporarily in a raw data file. |
| Array Processor | Data calculated into an image. Image is then transferred to host computer. |
| What does the slip ring transfer? | *electrical power *scanning instructions *detected signals between stationary components & rotating gantry components. |
| Name the benefits of multi-row detector CT. | *faster scans *increased anatomical coverage *scanning with thinner slices to improve resolution along the slice direction. |
| What is an electron beam CT (EBCT) scanner. | It is an alternative design that has no x-ray tube. It offers very fast scan times making it suited for cardiac & coronary artery imaging. |
| What does the EBCT produce? | An electron beam that streams from its electron gun & which is electro-magnetically directed toward an array of tungsten anodes. An x-ray beam is generatred when the elctron beam strikes the anodes. |
| Fusion imaging | Is the comparison of 2 imaging modalities yielding co-registered images. |
| There is great value in overlaying the PET image on the high-resolution CT image in order to what? | Associate la metabolism change with a specific structure. |
| The ________ _________ is the key point of interaction between the technologist & the imaging system. | Operator's console |
| The ______ ______ is the primary link between the tech & the other components of the imaging system. | Host computer |
| The spatial resolution of a CT imager can be improved by reducing what? | pixel size |
| Fourier transformation (FT) | a mathematical transformation to convert distance into spatial frequency. |
| Image Uniformity | refers to constant CT # of an object |
| CT spatial resolution can be improved by what 4 things? | 1. using a smaller pixel 2. thinner slice imaging 3. narrowing the predetector collimation 4. increasing the source to isocenter distance. |
| Fourier transformation (FT)is a method to: | 1. transform object size to spatial frequency. 2. change distance into inverse distance. |
| A Modulation Transfer function (MTF) can be used to estimate what? | spatial resolution at all spatial frequencies. |
| How is spatial resolution for CT usually expressed? | By the value of the spatial frequency at a 10% modulation transfer function (MTF). |
| Noise on a CT image principally influences what? | contrast resolution |
| Linearity is particularly important for what? | bone mineral measurement. |
| Linearity | is a property of a system, characterized by output that is directly proportional to the input. In CT, linearity describes the amount to which the CT # of a material is exactly proportional to the density of this material (in hounsfield units) |
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