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Terms in this set (129)
Which CT system is capable of helical scanning?
volume CT scanners
1. 3rd generation (960) detectors
2. 4th generation
3. EBCT - electronic beam CT
Which generation of CT scanner utilized a (360) degree rotation of the x-ray tube around the patient?
3rd generation scanner
Which generation of CT scanner utilizes a fixed ring of detectors?
4th generation (4800) detectors
What are the advantages of CT over conventional imaging?
1. Anatomical structures are visualized with no superimposition.
2. MPR - acquired data maybe reconstructed & viewed in alternate planes with no additional radiation to the patient.
3. Measure Attenuation
4. Manipulation of attenuation data - tissue attenuation data collected by detectors may be manipulated and measured by the computer.
What is the major advantage of helical CT over standard CT imaging?
1. Allows a volume of tissue to be examined rather than individual slices only.
2. Shorter scan times.
3. Artifacts caused by patient motion are reduced.
What CT component controls slice thickness?
postpatient collimation (per new text--previously prepatient)
What specifically do the CT detectors measure?
attenuation of the transmitted x-ray beam
What are clinical indications for CCT?
(CCT) = cranial computed tomography
2. circulatory pathology
3. inflammatory/infectious conditions
5. congenital abnormalities
7. degenerative disorders
What condition would be contraindication to CCT?
1. sensitivity to iodine (iondinated contrast)
2. prior contrast reactions
3. cardiac arrhythmias
4. renal failure
What meningeal space contains cerebrospinal fluid?
Which layer of the meninges is located close to the brain?
What is the name of the deep fissure that separates the two ceribral hemispheres?
What is the name of the white brain structure that connects the two cerebral hemispheres?
A condition due to an abnormal amount of CSF in the ventricles is termed?
Where is the cerebrospinal fluid manufactured?
choroid plexuses of lateral ventricles--500 ml per day
Which aspect of the forebrain helps regulate pain, temperature, and touch?
Which structure is also called hypophysis?
What are the structures of the brain stem?
mid brain, pons, and medulla
Which structure connects the two hemispheres of the cerebellum?
What structures of the brain are considered white brain matter?
myelinated axons - centrum semiovale & corpus callosum
(Grey Matter - dendrites & neuron cell body)
How many pairs of cranial nerves are found in the brain?
1. olfactory nerve (smell)
2 optic nerve (vision)
5. trigeminal nerve (mixed sensory and motor)
10. vagus nerve (sensory and motor)
What is the name of the site where the optic nerve cross in the brain?
About how long can the brain cells survive w/out oxygen?
approx 4 min.
The majority of CCT scans require IV contrast.
What are the components of the CT scan unit?
1. gantry( x-ray tube, collimator assembly, detector array, prepatient & postpatient collimator)
2. patient couch/table
4. operator console .
CT is able to distinguish differences in tissue densities as low as?
What is the average slice thickness for a routine CT exam of the chest?
5 mm slice (normal)
1 mm slice for high resolution
What are clinical indications for CT of the thorax?
tumors, circulatory pathology, trauma, imflammation/ infectious condition, pericardial disease, disease of the chest
What condition may place the patient at greater risk for a CT chest exam using iodinated contrast media?
prior reactions to contrast
Which position is used for most CT exams of the chest?
supine with arms above chest area
What type of attenuation does a tampon inserted during a CT exam of the pelvis create?
What is the name of the initial scan to determine the range or slice for the procedure?
scanogram, pilot, scout, topogram, or localizing scan
At what level does a CT abdomen scan routinely begin?
from diaphram to iliac crest
What is the name of the tapered, terminal part of the spinal cord?
Conus Medullaris (Cauda Equina is 1/2" inferior)
What type of neuron carries electric impulses away from the cell body?
Advantages of CR over conventional imaging
1.) can adjust the contrast or gray scale
2.) can display anatomy in a series of slices
3.) can measure attenuation of specific tissue
Windowing is used in CT for
adjustment of image contrast
Multi-slice CT scanners can acquire up to 4 slices simultaneously.
A tech can contol number of shades of gray assigned to a CT image.
An entire volume of tissue in a slice is called ?
Window width (ww) in CT refers to image contrast.
Which medium serves as the baseline for CT numbers?
Water = 0
5th Generation CT
Electron-Beam Computed Tomography (EBCT)
number representing the attenuation value for each pixel relative to water which is zero
voxels having the same cubic size; all voxels are isotropic
images acquired in axial plane can be reconstructed in coronal, sagittal or 3D
3D tissue, each pixel represents a voxel
1. 3D version of a pixel
2. are isotropic - all the same size
preliminary CT to plan a range of scans
transmits electricity & allows continuous rotation of the tube
brightness; CT number that occurs most frequently
(+1000 to -1000) contrast
wide window has many CT numbers, LOW CONTRAST
narrow window width have fewer CT numbers, HIGH CONTRAST
maximum intensity projection
Formation of CT image is a distinct 3-phase process
1. scanning phase produces data, but not an image
2. reconstruction phase processes the acquired data and forma a digital image
3. digital-to-analog conversion phase: the visible and displayed analog image (shades of grey--controlled by tech called CT numbers) is produced
for CT imaging a high kV (123-140) and heavy beam filtration is used
this minimizes the photoelectric interactions that are influenced by the Z of a material
1. ratio between couch speed and slice thickness
2. calculates the amount of anatomy examined during a particular multislice scan
3. pitch = couch movement (mm/sec) per 360° rotation/collimation (slice thickness)
* slower table increase in pitch (thin slices); fast table (thicker slices)
Typical dose per exam
radiation dose per slice 1500mr, but increases to 3000mr
occurs if more than recommended contrast
technology that uses optimal mAs per slice to minimize the patient dose
Bismuth Shields (in-plane shielding)
can be used to minimize dose to radiosensitive organs (eyes, breasts, pelvis, thyroid)--provides 57% radiation dose reduction
cushion the brain
Which of the following statements is not an advantage of CT over conventional imaging?
Exposes the patient to less radiation
The term windowing is used in CT for
adjustment of image brightness or contrast
What controls the actual thickness of the CT slices?
collimator & pitch
The number and shades of gray assigned to a CT image can be controlled by the technologist.
An entire volume of tissue in a slice is called a voxel.
The gantry houses the CT tube and the array of detectors.
CT number Range
cortical bone +1000 to +3000 white
white matter +45 light grey
blood +20 grey
water 0 (baseline)
fat -100 dark grey
air -1000 black
Which of the following would not apply to head CT?
Which of the following may be a contraindication for head CT?
sensitivity to iodinated contrast media
Liver metastasis is difficult to diagnose with CT.
If a patient has sensitivity to iodinated contrast media, which of the following conditions may be a contraindication for head CT?
glioma (tumor)--do MRI instead
the solid spinal cord terminates at what lower level of which vertebrae?
The name given to large venous blood channels in the skull?
The thin outer cerebral cortex is classified as grey matter.
What is the 1st cranial nerve?
What part of the brain controls coordination and balance?
Volume CT scanners are limited to one 360° rotation per slice in the same direction.
Pixels represent varying degrees of
Air has a CT number of
Bone has a CT number of
Current multi-slice CT scanners can acquire at least 64 slices simultaneously.
Iodinated contrast media is able to pass through the BBB in the normal individual.
The number and shades of grey assigned to a CT image can be controlled by the technologist.
What type of artifact is produced by a defective detector?
Two other terms for volume scanning are
Pitch ratio is the ratio between table speed and slice thickness. Which of the following pitch ratio represents undersampling?
For a volume CT scan of the thorax, the patient must be able to hold their breath for at least
Which device in the helical CT scanners allow continual tube rotation in the same direction?
What must be done to the numerical data to create the actual CT image?
assign various shades of grey to numeric values (done by computer)
Contrast media will not normally cross the
Considering the BBB, which would require the use of contrast media?
possible neoplasm & brain tumor
In what year did the first successful clinical demonstration of CT take place?
Enlarged regions of the subarachnoid space are called
cisterns (injection site--cisterna magna)
The largest region of cisterns that is inferior to the 4th ventricle.
The cerebral cortex and cerebral nuclei are considered to be grey matter.
(white matter - axons, corpus callosum, centrum semiovale)
What are the 3 primary structures of the brain stem?
medulla, midbrain, pons
Which of the following is not a pathologic indication for CT of the thorax?
mitral valve prolapse (heart--more specialized)
Beam hardening for CT of the abdomen will most likely occur when
high concentration of a large bolus of barium is present with a low concentration of water.
5% water soluble or diatrizoate
Gastrografin is desirable as the GI contrast agent because it will slow peristaltic action.
false (gastrografin increases peristalsis--good for CT)
The primary difference between each generation of CT scanners was the number and arrangement of detectors.
Non-invasive studies of the heart are possible with multislice CT.
The depth of a voxel is determined by
Pitch is a relationship between
table speed and slice thickness
What contrast media is used for CT virtual endoscopic procedures?
air or carbon dioxide
CT angiography does not require the use of iodinated contrast media.
The use of CT has reduced the ERCP as a common diagnostic procedure for evaluating the bile ducts.
The use of water soluble contrast agents rather than barium for GI tract examinations is desirable in CT because they tend to slow peristaltic action.
Because of short exposure times, patients are not required to hold their breath during CT exposures of the abdomen.
The use of oral and rectal contrast media is essential for CT abdominal and pelvic exams.
A topogram is completed at the end of a CT series.
CT of the head to image the bones (bone window) should be done with a wide window.
Which generation of CT scanner used a pencil-thin beam and a single detector?
Which of the following pathologic indications does not aply to cranial CT?
hilar neoplasia (kidneys)
Considering the BBB phenomenon, which of the following would require the use of contrast media?
1. possible neoplasia
2. brain tumor
A _____ slice thickness is commonly used for routine scans of the thorax.
The uncinate process refers to
the hooklike extension of the head of the pancreas
Beam hardening artifacts are most likely to occur when
high concentration of barium
What must be done to the numerical data to create the actual CT image/picture?
Assign various shades of grey to numeric
Contrast media will not ordinarily cross the
Name one anatomical site that can be imaged with virtual CT endoscopy.
The part of the neuron that conducts impulses away from the cell body is
Three protective membranes that cover the CNS are called
what is the name of the area that connects the 3rd and 4th ventricles?
aqueduct of silvius or cerebral aqueduct
Describe the collimators used in CT
1. prepatient (source) collimator
2. postpatient collimator
CT pathologic indications Brain
neoplasm, masses lesions
trauma (hematomas, fractures)
CT pathologic indications Chest
mediastinal and hilar mass
abscess or cyst
cardiac disease, pericardial effusion
dissection of aorta
CT pathologic indications Abdomen
primary or metastatic lesions
hepatic or splenic hematomas
CT pathologic indications Pelvis
prostate, uninary bladder, ovarian carcinoma
soft tissue masses
exclude an occult disease (unknown)
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