Imaging protocols Flashcards
In the simultaneous acquisition dual-isotope protocol, when are the resting thall-201 images acquired relative to the stress tech-99m?
a. before
b. at the same time
c. after
d. On a separate day
B.
For simultaneous acquisition protocol, the resting thall 201 and stress tech-99m perfusion images are acquired at the same time. This protocol simplifies acquisition and relies on the use of multiple energy windows to acquire the lower energy thall-201 at teh same time as the higher energy tech-99m. A third window is used to correct for the down scatter of the higher energy tech-99m into the lower thallium-201 window. The pt is first injected with thall-201, usually at the normal dose of 3-4millicuries, adn then stress is performed using a lower dose 9-15 of tech-99m. This allows a single acquisition and saves total protocol time.
What is the most typical image artifact due to pt motion during SPECT acquisition?
a. ramp
b. hurricane
c. ring
d. skewed
B.
Pt motion in the vertical, horizontal, or rotational planes causes decreased counts in walls that are contralateral or 180 degrees opposite to each other and usually do not follow coronary artery territory distributions. At the edges of the defects tails or streaming effects may be noted and are responsible for the hurricane appearance, whcih gives this artifact a name. Motion correction may be used to ompensate movement, but it can only correct in the vertical plane. Horizontal and rotational motions are much more difficult to detect on the raw projection images and cannot be corrected.
What is the most likely cause of the abnormality noted in the bull’s-eye display, for a rest/stress rubidium-82 PET perfusion study?
a. incorrect definition of the long axis
b. incorrect definition of the base slice
c. incorrect definition of the apex
d. incorrect alignment of the stress/rest
B
What is the minimum peak pixel count the LV myocardium on a planar tech-99m SPECT projection that is recommended to obtain best-quality interpretable images?
a. 50
b. 100
c. 150
d. 200
D.
The greater the number of counts in the myocardium, the higher the quality of the images and the more accurate the interpretation. A minimum of 200 counts/pixel using tech-99m and 100counts/pixel using thall-201 in the myocardium on an anterior projection is recommended. Fewer counts will introduce artifacts due to poor performance of the reconstrution filters, which are usually fixed regardless of the total counts acquired. Total number of counts is influenced by the following: body habitus/bmi, level of exercise or pharmacologic stress, administered dose of radiopharmaceutical, acquisition time, energy window, and the type of collimator. Dose infiltratoin at the IV insertion site and residual activity in the injection syringe may lower the total dose received by the patient. This means that the delivered dose into the pt is less than measured dose from the dose callibrator.
Which of the following parameters will increase the total counts acquired on a SPECT tech-99m study?
a. continuous acquisition
b. high resolution collimation
c. narrow energy window
d. ECG gating
A.
Continuous acquisition allows the gamma camera to acquire counts while it is rotating form one position to the next and increases total counts by eliminating the dead time during camera motion assoc with conventional step and shoot acquisition. There may be image blurring due to motion the higher counts and appropriate filtering can eliminate these.
High resolution collimation decreases total counts relative to the use of a general all-purpose collimator.
Narrowing the energy window will lower the total counts. ECG gating has minimal effect on counts. If only one channel is used to simultaneously acquire the perfusion adn gated information and arrhythmia rejection applied, rejected beats will lower the total number of counts in the perfusion images due to beat rejection. It is then recommended that a large acceptance window be used.
Which of the following is most likely to cause TID of the LV on SPECT perfusion imaging?
a. mild AS
b. mitral regurg
c. microvascular CAD
d. NICMO
C.
Typically TID is caused by severe, multivessel prox epicardial CAD, causing subendocardial ischemia that makes the walls of the LV look thinner and the cavity bigger relative to the resting study. Microvascular CAD may also result in TID.
Severe AS may cause subendocaridal ischemia in the absence of epicardial or microvascular CAD due to an increase in wall tension with exercise/vasodilator stress.
MR should decrease LV volume due to an increase in regurgitation fraction, and decrease in diastole in stress.
NICMO in the absence of CAD should have increased LV volumes at rest and stress w/o visually noticeable changes.
What is the minimum number of acquisition projections or stops recommended for spect acquisition over 180degrees using tech-99m radiotracers?
a. 20
b. 40
c. 60
d. 80
C.
The number of recommended projections is related to the optimal resolution of the imaging system. Since tech-99m images provide higher resolutoin, the minimum # of projections recommended is 60-64. For thall-201 32 is acceptable
What is the best reason to use 16 ecg-gated frames for tech-99m images SPECT acquisition?
a. Higher counts in each frame
b. assessment of diastolic fxn
c. improved perfusion spatial resolution
d. better averaging of end systole for more accurate EF
B.
With 16 frames there is adequate temporal resolution to accurately assess the 4 phases of diastolic filling and measure peak filling rate and the time to peak filling rate. 8 frames is insufficient temporal sampling.
During filtered back projection reconstruction of SPECT tech-99m images, what effect does overfiltering have on the perfusion images?
a. leaves too much contrast
b. leaves too little contrast
c. accentuates ramp artifacts
d. improves detection of disease
B.
Overfiltering spect perfusion images, which generally have a low signal-to-noise ratio, makes the images too smooth and leaves too little contrast so that there is a loss of info and d a tendency to decrease sensitivity for CAD. Typically, Hanning or Butterworht filters are used with filtered back projection and cutoff frequencies are preset and kept constant for all studies to provide a consistency in the images generated.
Ramp filter artifacts are caused by the second filter applied during filtered back projection and are less affected by overfiltering. Filters with cutoff frequencies that vary depending on the acutal measured signal-to-noise ratio are available.
What is the mechanism by which prone imaging improves diagnostic accuracy in SPECT perfusion imaging?
a. correcting for attenuation
b. shifting the location of attenuation
c. decreasing patient motion
d. shortening imaging time
B.
Prone imaging was initially used to get greater separation between inferior wall of the heart and the diaphragm in order to differentiate an inferior wall infarct form normal loss in counts caused by the diaphragm. Prone imaging shifts the location relative to supine positioning, and the change in attenuation assoc with the change in position can be compared. If a defect is caused by attenuation the location will shift with a shift in body position while a true infarct will be present regardless. Subsequent studies have shown prone imaging improves identification of both breast and chest wall fat attenuation by observing the shift in attenuation position. Obese pts may find it uncomfortable and have to move.
When performing SPECT thall-201 imaging, how many different energy peaks can be acquired to max counts?
a. 1
b. 2
c. 3
d. 4
C.
The majority of thall-201 emission is predominately at the lower 70kev peak, which is routinely imaged, but there are also peaks at 135 and 167 kev. Newer cameras allow acquisition at multiple energy windows and all 3 peaks should be utilized to increase counts and improve image quality. By increasing counts the thall-201 dose administered can be reduced to lower pt exposure.
What is the best explanation for why emission (perfusion) and transmission (CT for attenuation correction) registration must be verified when using hybrid spect/ct and pet/ct systems for rest/stress perfusion imaging?
a. patient change beds between emission and transmission acquisition
b. emission and transmission images are acquired simultaneously
c. minor motion and respiratory changes can cause artifacts
d. not necessary but a recommended quality control measuare
C.
Hybrid systems have a CT and gamma camera gantries that are contiguous and pts are moved on the table from one system into the other. Bed changes are not required. CT adn emission studies are acquired sequentially, not simultaneously so that there is time adn opportunity to shift position between the 2 studies and even minor motion such as that due to normal or exaggerated breathing, in any dimension will cause misregistration and inappropriate adding or subtracting of counts during attenuation correction.
Which of the following quality control measurements for spect systems is required on a daily basis?
a. uniformity
b. center of rotation
c. sensitivity
d. resolution and linearity
A.
Uniformity testing and energy peaking are required on a daily basis. Center of rotation is mandatory but varies with the system and is usually not a daily requirement. Some systems have built in verification and correction of center of rotation. Sensitivity testing is an optional measurement. Resolution and linearity are recommended and vary with the manufacturer but neither is required on a daily basis.
A 69 yo male ahs a history of a prior infarct and PCI. He is now having right-sided CP and is referred for pharm dual isotop MPI. Based on fig 4.2 what is most likely diagnosis?
a normal
b. lat wall ischemia and infarct
c. septal ischemia
d. septal infarction
C.
