Motherload Dx Imaging Final
Which of the following frequencies would include diagnostic ultrasound?
10 MHz
One Tessla is equal to:
10,000 gauss
In general, restriction of the primary beam with cones or collimators requires that the device restrict the beam to an area whose measured dimensions differ form the desired dimensions by no more than.......of SID
2%
The LD of humans is close to:
300 rads
For lung and prostate malignant tumors, a typical course of radiation treatments will result in a cumulative dose of approximately:
7000 rads
Which of the following is not part of the law of Bergonie and Tribondeau (increased tissue metabolic activity, increased tissue radiosensitivity)?
A fetus is less radiosensitive than an adult
A minimal x-ray exam of a body part includes:
AP and lateral views
The 10 day rule states that:
Appropriate x-ray exams should be scheduled within 10 days after the onset of menstruation
What is the depth of the voxel determined by?
Bem
No film ->
CT and MRI
Do x-rays or CT's collimate better?
CT's collimate 2X better than x-rays
What are MRI's really good at?
Contrast resolution AKA soft tissue contrast
Of the various macromolecules sensitive to radiation damage,......is/are considered most sensitive
DNA
Transverse relaxation is also called:
Spin-spin relaxation
A minimal MRI exam of a body part includes:
T1 and T2 weighted images
A CT image matrix is listed at 512 by 512. What does this mean?
The anatomical image is composed of more than 200,000 picture elements
Why is MRI non-ionizing?
The electron-binding force of atoms that make up human tissues is greater than the energies associated with the main magnetic field and the radiofrequencies used in MRI
True or false: Sonography is ideal for imaging lungs due to non-ionizing nature
False
True or false: There is a minimum amount of radiation a human can tolerate, less than 100 mR, with no adverse biological effects
False
What is the sensitivity of an atom to its magnetic field?
Gyromagnetic ratio
The primary biologically reactive molecular byproducts formed during the radiolysis of water are thought to be:
H+ and OH-
Which of the following has the highest gyromagnetic ratio?
Hydrogen
The single most important advantage of spiral CT is which of the following?
Imaging a large volume of anatomy in one breath hold
The units of gyromagnetic ratio (atom's sensitivity to magnetic field) associated with polar protons are expressed as:
MHz/T
Which of the following technologies has the best contrast resolution?
MRI
Free induction decay =
Nuclear relaxation in which RF signal (radiation) is emitted
Fusion scans man combine.....and.....images
PET, CT
If a small anatomical detail occupies less volume than that of one voxel which its is being projected, that detail may be rendered visible. This is an example of:
Partial volume averaging
The principle on which ultrasound is based is called the......effect
Piezoelectric
Considering MRI physics, during nuclear relaxation:
Radiation is emitted
A CT scan is made with a 0.5 mm slice thickness and a 0.5 mm pixel size. What is the size of the voxel?
(pixel size)^3 = (0.5)^3 = 0.125 mm Length X width X height (0.5) X (0.5) X (0.5)
The whole body radiation dose encountered in a technetium bone scan is approximately how many rads?
0.2
The generally accepted range of useful densities on a radiograph is.....above base + fog
0.5 - 2.5
Lines on radiographs running perpendicular to the direction of the film traveling through the processor are:
1. An indication of dirty rollers 2. Usually repeated every 3.14 inches
The MRI image appearance is determined by which of the following?
1. T1 relaxation time (white bone) 2. T2 relaxation time (dark bone) 3. Spin density
The cardinal principles of radiation protection is/are:
1. Time 2. Distance 3. Shielding
Assuming a FFD of 72 inches, which is the maximum allowable deviation of the collimation from the actual x-ray beam size?
1.2 inches
Diagnostic ultrasound intensity is measured in:
W/cm squared
Do x-rays or CT's have better spatial resolution?
X-rays have 2X better spatial resolution
What do x-rays do better than CT's? What do CT's do better than x-rays?
X-rays have 2X better spatial resolution and CT's collimate 2X better
Probably the greatest hazard associated with MRI is:
a projectile
A CT scanner initially obtains adult images in which plane?
axial
A minimal CT exam of a body part includes:
bone and soft tissue windows
If all other factors remain constant, radiation dose is related source to object distance.....
by the inverse square law
The medical physicist.......accurately relate the dose in mR, millirads or millirems form only the technique factors set into the xray machines
cannot
Bone window =
close to 1000
Spin density can be defined as hydrogen.....
concentration (because Hydrogen has highest gyromagnetic ratio and thus spin density)
Which of the following will always appear black on MRI regardless of the pulse sequence?
cortical bone
If all the other factors remain constant, radiation does is related to xray beam on time.....
directly
The exchange of......between two systems of a specific......is called......
energy, frequency, resonance
The RF signal emitted by tissues following RF excitation is called a:
free induction decay
The more narrow the CT window setting the......the contrast of the displayed image
greater
A hypothesized bioeffect of increasingly stronger MRI magnet strength is:
heating
Radiation induced damage in biological tissues:
is treated in the presence of increased oxygen levels of the tissue is being radiated
Voxels are:
isotropic
The rate of precesion of any polar portion of any element is called its:
larmor frequency
Radiation production guidelines in US are based on which type of dose-response relationship?
linear non threshold
The ability of an xray machine to produce constant radiation output at various conditions of mA and exposure time producing the same mAs is called:
linearity
Soft tissue window =
low - close to 0-30
A Hounsfield Unit:
numerical value of a pixel
Hot spots on a static bone scan image corresponds to:
osteogenic activity
Dose fractionation is less effective than a single dose of therapeutic radiation because:
recovery occurs between doses
Radionucleotide imaging is a......and......imaging modality
sensitive, nonspecific
The diagnostically useful portion of a characteristic curve mostly includes the......portion of the curve
straight line
The weakest link in the chain of diagnostic imaging is:
the processing system
All of the following are contraindications for MRI except:
total hip replacements
Spiral CT scans have:
very very fast scan times
T1 = T2 =
white bone dark bone
