Notes from Mosby's Exam Review Flashcards
what is the formula to calculate HU (CT number) of a tissue given the linear attenuation coefficient of water and the tissue for a particular scanner
(LAC of tissue - LAC of water) / LAC of water * 1000 {in other words: LAC of tissue minus LAC of water divided by LAC of water * 1000 }
The phantom measurement of the uniformity* of a CT system is performed primarily to assess the negative effects of:
Beam hardening
Which of the following components of the CT image quality may be controlled by the technologist? 1. spacial resolution 2. contrast resolution 3. noise
all of the above
What is the major controlling factor of exam quality for coronary CTA?
patient heart rate. Stable, steady heart rates below 65-70 beats per minute (bpm) yield the best results
What is the purpose of automatic tube current modulation (ATCM) software in the CT system?
decrease patient dose. It is a form of AEC (automatic exposure control)
Which two technical factors play a role in the production of an isotropic dataset?
section width and display field of view (DFOV) NOT the SFOV
What is the term that refers to the measured time in seconds required for blood to pass through an area of the brain tissue:
mean transit time (MTT)
What kind of scatter accounts for the primary interaction between x-ray photons and tissue during computed tomography?
compton effect
At what level of the spine does the abdominal aorta split into the right and left iliac arteries?
L4
What is happening in the heart during ventricular systole?
contraction of the left and right ventricles
What degree of azimuth setting is used to make a localizer or scout image?
0 degree - a 0 degree azimuth describes the situation in which the x-ray tube and detectors do not rotate but remain above and below the patient, providing a frontal projection
In multislice CT (MSCT), the beam pitch is equal to the table feed per rotation divided by the _______.
total collimation (total collimation is equal to the combined thickness of all of the sections that are simultaneously acquired with each gantry rotation
In what phase of contrast will you see well-opacified ureters?
excretory
What is the approximate CT density (in HU) of the density of the unenhanced spleen?
between +40 and +60 HU
What is a hallmark finding for focal nodular hyerplasia (FNH) of the liver in CT? (hint: it has to do with how it enhances with contrast)
central scar that remains hypodense after initial contrast agent administration
As a solid-state CT detector measures transmitted radiation, it emits a proportional response in the form of _____. (analog or digital signal)
analog signal - (it passes this signal to the ADC)
What is the word for the spread of infection through a contaminated object?
fomite
What should a PET-CT patient avoid prior to their test so that abnormal uptake is not registered in muscle?
strenuous activity (because this will make the FDG uptake in the muscle
What is the unit of effective dose?
sieverts (Sv)
A voxel whose attenuation coefficient is less than that of water is assigned a pixel value with a _____ CT number
negative
What is used to treat a severe vagal reaction to iodinated contrast that includes bradycardia?
atropine
How thin do we scan high-res chests?
1 mm
In patients who are right dominant, the posterior descending artery branches from this coronary atery?
The right coronary artery
What type of reconstruction was used in the first prototype CT scanner?
iterative technique
Are both the kidneys and pancreas considered to be restroperitoneal?
yes
Does IV contrast improve the differentiation of subtle hemorrhage in the brain?
No. Contrast is initially contraindicated because the enhancement may actually mask subtle signs of hemorrhage
How does single-segment reconstruction change the temporal resolution
using single-segment aka. half-scan will half the temporal resolution. Ie. a 400-msec rotation scan will be 200-msec when reconstructed with single segment
What is the optimum contrast phase for kidney lesions and when does it occur.
The nephrographic phase and it occurs between 70 and 90 seconds after the start of injection
What is the definition of pitch?
It is the relation of table speed to slice thickness
What is the formula to calculate pitch?
Pitch = travel distance of table per 360 degree rotation divided by the total xray beam collimation width. pitch = TD/TCW
The approximate inherent filtration of the tube housing, cooling oil, and so on amount to how thick of aluminum equivalent filtration?
3.0 mm
That is the excretion half-time of intravenous iodinated contrast media in a patient with normal renal function?
1 to 2 hours
What does the symbol “x” stand for in the lambert-beer law?
the absorber thickness
What is the term for CT images being reconstructed for only a portion of the raw data to reduce motion artifact?
subtraction images
What kind of tissue are ‘low spacial frequency’ algorithms best at demonstrating?
soft tissue detail (they filter out high spacial frequency information such as bone)
What scanning acquisition mode is used to scan prospectively ECG-gated cardiac CTA studies? (axial “step-and-shoot” or spiral)
axial “step-and-shoot”
What DFOV is commonly used to reconstruct images of the spine?
120 - 150 mm or 12 - 15 cm
A dermoid tumor of the ovary may also be referred to as ____
cystic teratoma
What is the single worst element working against a CT scanner’s contrast resolution?
noise
Name the two technological advances that enabled spiral/helical CT scanning?
slip-ring technology and high-efficiency x-ray tubes
Name two common areas of calcification in the brain.
choroid plexus and pineal gland
When performing both a CT abdomen and conventional GI studies, which should be done first and why?
The CT should be done first because the heavier barium used in GI studies causes streak artifact on CT.
How high an osmolality is high-osmolar contrast material?
1000-2400 mOsm/kg water
Who was the 1917 austrian mathematician who proved that it was possible to reconstruct a three-dimensional object from the infinite set of all of its projections
Radon
The condition whereby a portion of the small intestine collapses or telescopes into itself is termed:
intussusception
During a CT scan, each sample of ray sum measurements made by the data acquisition system (DAS) is called _____
view
By CT criteria, a solitary pulmonary nodule may be defined as a focal area of increased density in the lung that is smaller than ____cm
3 cm
What three things are going on when there is ‘complete cardiac diastole’?
relaxation of the left and right ventricles, relaxation of the left and right atria, the T wave of the electrocardiogram (ECG)
What is the typical HU range for modern CT scanners?
-1024 to +3071
How much mL/100g cerebral blood volume (CBV) indicates a brain parenchyma infarct core?
2.5 mL/100g
How is a vasovagal reaction linked to blood pressue?
The term vasovagal pertains to systemic hypertension (often leading to cerebral ischemia)
What does the modulation transfer function (MTF) of a CT scanner measure?
It’s ability to faithfully reproduce the anatomy that is being imaged
What is the range of values for modulation transfer function (MTF) that describe how well the anatomy that is being imaged is reproduced?
0 to 1. 0 is said to have no useful informatioin and 1 is said to be perfect. Most scanners are somewhere in between.
What HU range is a solitary pulmonary nodule though to be benign?
165-200 HU
Between spondylolisthesis and retrolishesis, which is a forward slipping and which is a backwards slipping?
spondylotisthesis is a forward slipping and retrolisthesis is a backwards slipping
What percentage of it’s blood supply does the liver receive from the hepatic artery vs the portal vein?
25% from the hepatic artery and 75% from the portal vein
What HU unit is associated with calcium (such as in the coronary artery)?
+130
What is a standard section width (aka slice thickness) and interval (aka slice gap or incriment) used for an abdomen and pelvis scan
3.0/3.0 mm- 5.0/5.0 mm
How many shades of gray is the human eye capable of differentiating?
60-80
Each 1% difference in contrast between adjacent objects amounts to a difference in pixel value of how much (in HU)
10 HU
What is the term for too much nitrogenous material in the blood?
azotemia or uremia
Neoplasms in what body part is most commonly treated with CT-guided radio frequency ablation (RFA)
liver
What stage of an ECG will the heart demonstrate the least motion?
T wave
What is quantitative computed tomography (QCT) used to measure?
the mineral content of bone. You can calculate the BMD values (bone mineral density)
What is the average volume of contrast for a CT myelogram
12-14 mL
How long after contrast should a breastfeeding mother “pump-and-dump”
12-24 hours
What is the purpose of doing the expiration part of a high-res chest?
to look for air trapping from COPD
A patient with an elevated level of D dimer in the bloodstream may be at increased risk for which serious condition?
pulmonary embolism (PE)
CT scanning of the liver for tumor evaluation should not be performed during which phase?
Equilibrium phase because it can hide hepatic lesions.
The acronym PTT is used for which laboratory test?
Partial Thromboplastin Time - it indicates the coagulation time of a patients blood
The portion of the male reproductive system responsible for the storage of the majority of the mature sperm is:
vas deferens
What ligament suspends the duodenum from the diaphragm?
ligament of treitz
When trying to display images with varying density ranges (ie. mastoid tip and IACs in same image) should you use a wide or narrow window width?
a wide window width, such as 4000, should be used
When trying to display images with many similar densities, (like abdomen) should you choose a wide or narrow window width.
a narrow window width, such as 400 will better display an image with many similar densities.
What kind of detector array contains mid line narrow elements flanked by wider detectors?
a hybrid array
The technique that allows the user to select the range of pixel values used in a 3D CT reformation is termed:
thresholding. It is what allows your render to just include bone, for instance, and not the unwanted soft tissues
The normal range for the International Normalized Ratio (INR) for prothrombin time (PT) results is:
0.8 - 1.2
Which phase of contrast provides the best gastric and intestinal wall enhancement? (think ABD/PEL W)
portal venous phase
Is transdermal a route of paraenteral medication administration?
No it is not. But subcutaneous and intradermal are. Paraenteral = infusion or injection
For MDCT, identified areas of calcium must demonstrate relative attenuation values greater than:
+130
The calculation of the average cumulative dose to each section within an acquisition of multiple sections is termed the:
MSAD or Multiple Scan Average Dose
Which window width and level would be good to look at CT colonography images?
Width = 1600, Level=-400 (a “lung-type” setting)
What relationship is there between the slice width and gap when wanting an overlapping slice?
The section interval (slice gap) must be less than the section width (slice thickness)
Axial CT sections of the lumbar spine for intervertebral disc evaluation is best done in which plane (think MR)
parallel to the plane of the intervertebral disc spaces
The quantity of radiation dose received by the patient from a series of CT scans is referred to as:
MSAD (Multiple-Scan Average Dose)
What are some of the signs and symptoms of hypovolemic shock?
pallor, hypotension, tachycardia, oliguria (decreased urine production)
Do gallstones appear hyperdense on abdominal CT scans?
Yes!
What does intrathecal mean?
occurring within or administered into the spinal theca
Is reduction in patient dose an improvment of chest CTs with MDCT (multidetector CT)?
No. While you get increased speed and a reduction in the misregistration artifacts, the dose from MDCT on chests is actually higher than single-slice CT.
Which two major conditions is D dimer used to asses?
PE (pulmonary embolism) and DVT (deep vein thrombosis) - basically stuff to do with blood clots.
Are the following three contrast agents ever used in imaging of the chest? diatriozoate meglumine, barium sulphate, iopamidol
yes! all three are.
What is the term used to describe a portion of a herniated intervertebral disc that has migrated from its normal position?
sequestered disc
what type of isolation is used for patients at risk for infection due to immunosuppression?
“strict” isolation
The normal range of cerebral blood volume (CBV) contained within 100g of brain tissue is
4-5 ml/100g
In patients who are left dominant, the posterior descending artery branches from the _____.
left circumflex artery
What is capable of causing an edge gradient artifact?
dense bone (occurs at areas of abrupt change in density)
The perimetrum, myometrium, and endometrium are all parts of which structure?
uterus
In addition to anatomic location of tumor activity, what other role does CT play in PET-CT studies?
attenuation correction of emitted photons
The approximate radiation dose measured during a scan of a 100-mm pencil ionization chamber is termed the ____.
CTDI
What is the maximum allowable blood glucose measurement for patients scheduled to undergo PET-CT examination?
150 mg/dl
When you measure the standard deviation in a water phantom, what negative thing are you really trying to measure?
Noise.
What is the only effective method of reducing streak artifact due to metal?
removing the object from the scan field.
Areas of a CT image containing abrupt changes in tissue density are electronically represented by what kind of spatial frequencies?
high spatial frequencies
The articulation between the distal tibia and fibula is called the _____.
syndesmosis
By using prospective ECG gating for cardiac CT over retrospective ECG gating you can _____ the patient radiation dose.
reduce
drainage-secretion precautions, enteric precautions, acid-fast bacillus, repiratory, contact, and strict, are all categories of _____ technique
isolations techniques
Decreasing mAs, increasing pitch, and decreasing KVp all do what to pt dose?
they all will decrease patient dose
What will increasing the pitch do to partial volume averaging?
It will increase the partial volume averaging effect
What is the unit of absorbed dose?
grays (Gy)
What is the normal respiration rate for an adult?
12-20 breaths per minute
140,000 - 440,000/mL of blood is the normal _____ count for an adult.
platelet count
The iliac artery bifurcates into the internal and external iliac arteries at about the level of what?
L5-S1
What negative oral contrast agent offers the BEST visualization of the enhancing GI wall on post-IV contrast CT exam?
water
A _____ spatial frquency algorithm will give the greatest soft tissue detail
Low Spacial Frequency
Two pixels have a difference of 1 HU. What percentage of difference does this represent?
0.1%
Why would you not use a small scan FOV in the hip?
it would cause an out-of-field artifact
What can assist in visualizing the vagina during a CT study of the pelvis?
Tampon insertion
What is a normal systolic blood pressure in adults?
95-140
simultaneous reconstruction, ray-by-ray correction, point-by-point correction - are all types of what kind of CT reconstruction?
iterative method
Which two generations of scanners used a translate-rotate mode of CT data acquisition?
1st and 2nd gen
3 mg/kg body weight of IV contrast should not be exceeded in what patient group?
children
A ___ spacial frequency algorithm is best at showing bony detail.
high
What percentage of iodine do water-soluble oral contrast agents (gastrografin) contain when the patient drinks it?
2%-5%
Are nausea and a warm, flush feeling examples of mild adverse reactions to IV contrast?
yes
What portion of the nephron is responsible for filtration of unwanted materials from the blood plasma?
glomerulus
What two terms are used to describe a CT scanner’s ability to differentiate objects with similar linear attention coefficients?
contrast resolution and sensitivity
CT images of the abdomen should be acquired with the patient a. at full inspiration or b. with the patient at full expiration?
b. full expiration. because this is the most reproducible point of the respiratory cycle.
What is formula to calculate the smallest object that a CT scanner can resolve give the limiting resolution in lp/cm
reciprical value of lp/cm x 10 to first number. divide out and split in half. eg. 15 lp/cm = 1/15 Lp/cm = 10/15 Lp/mm = .6 split in half =.3
A CT scanner with a limiting resolution of 15 lp/cm can resolve an object as small as ____.
0.3 mm
What is the name of the photons that the detector of a PET system is sensitive to?
annihilation photons
During CT colonography examinations, tagged fecal matter appears _____ on the image
white
CBF = CBV/MTT is the formula illustrating what principle?
the central volume principle of cerebral perfusion
Is it ionic or nonionic contrast that dissociate into charged particles when placed into solution?
ionic
What is the normal BUN range?
5-20 mg/dl
What two factors affect the longitudinal spacial resolution?
detector pitch and interpolation algorithm
What vertebrae are the kidneys located between?
T12 and L3
An Agatston score of 5 on an MDCT cardiac examination for coronary artery calcification is rated as:
minimal
Is using tape an acceptable method of immobilization?
No, it could damage skin
CT images that have been reconstructed from a portion of the data acquisition process in the hopes of reducing patient motion artifacts are called _____.
segmented images
Do you need IV contrast to evaluate for a renal cyst? (think of our protocol at CCHS)
Yes, you need to determine if it enhances
What is the normal percentage of barium sulfate in the suspensions used in CT?
only 1%-3%
The multiple-scan average dose (MSAD) is used to quantify the radiation dose received by the patient from a sereis of CT scans. True or false?
True!
What is the term used to describe the ability of an object to attenuate the x-ray beam?
linear attenuation coefficient (and only later to calculate the HU)
Which layer of the uterine wall brightly enhances after IV contrast administration?
myometrium
When scanning a smaller body part, like a shoulder, would you use a large or small SCAN field of view?
you would still use a large scan FOV to avoid out-of-field artifact and then reconstruct with a smaller display FOV.
The majority of pancreatic tumors occur in what part of the pancreas?
The head
Is transdermal a parenteral route of medication administration?
No.
The corticomedullary phase is a _____ arterial phase (early or late).
late arterial phase at 30-40 seconds
What is the best contrast phase to look at the pancreas?
arterial phase
What phase of contrast hides hepatic lesions?
equilibrium phase
Prothrombin time (PT) and partial throboplastin time (PTT) are both used to measure what?
blood coagulation ability
20-30 breaths per minute is the normal range of respiration what what age group of patient patient?
a child
What imaging plane do we not normally care about with IACs?
Sagittal (we usually do axial and coronal)
What is the term for stones within the gallbladder?
cholelithiasis
