1 Answer C. Double-inversion recovery sequence in black blood cardiac imaging is designed to suppress the signal from blood flow.

Reference: Ginat DT, Fong MW, Tuttle DJ, et al. Cardiac imaging: part 1, MR pulse sequences, imaging planes, and basic anatomy. AJR Am J Roentgenol 2011;197(4):808-815. doi: 10.2214/AJR.10.7231.

2 Answer B. With filtered-back projection, tube current is inversely proportional to noise. That is, increasing the mA by factor of 4 will yield half the noise (1/square root of 4). Tube current determines the number of photons generated and noise.

Reference: Litmanovich DE, Tack DM, Shahrzad M, et al. Dose reduction in cardiothoracic CT: review of currently available methods. Radiographics 2014;34(6):1469-1489. doi: 10.1148/rg.346140084.

3 Answer B. With filtered-back projection, tube current is inversely proportional to noise. That is, increasing the mA by factor of 4 will yield half the noise (1/square root of 4). Relationship of kVp to noise is complex, but in general, decreasing the kVp will increase the noise if other factors are held constant.

Reference: Litmanovich DE, Tack DM, Shahrzad M, et al. Dose reduction in cardiothoracic CT: review of currently available methods. Radiographics 2014;34(6):1469-1489. doi: 10.1148/rg.346140084.

4 Answer B. Effective tube current-time product is obtained by multiplying the rotation time by the mA and then dividing by the pitch. So in this case 0.3 × 700 = 210 mA, which is then divided by 0.2, giving 1,050 mA.

Reference: Litmanovich DE, Tack DM, Shahrzad M, et al. Dose reduction in cardiothoracic CT: review of currently available methods. Radiographics 2014;34(6):1469-1489. doi: 10.1148/rg.346140084.

5 Answer B. Reconstruction algorithm/kernel does not affect radiation dose since it is applied after the study is already obtained. It can affect spatial resolution and noise depending on which algorithm/kernel is used.

Reference: Litmanovich DE, Tack DM, Shahrzad M, et al. Dose reduction in cardiothoracic CT: review of currently available methods. Radiographics 2014;34(6):1469-1489. doi: 10.1148/rg.346140084.

6 Answer B. DLP is obtained by multiplying the CTDIvol by the scan length; therefore, it is directly proportional.

Reference: Litmanovich DE, Tack DM, Shahrzad M, et al. Dose reduction in cardiothoracic CT: review of currently available methods. Radiographics 2014;34(6):1469-1489. doi: 10.1148/rg.346140084.

7 Answer A. Effective dose gives a general population risk rather than patient-specific risk. It is obtained by multiplying the DLP by a conversion factor (f). The conversion factor is obtained by Monte Carlo simulation, and the best estimates (f) factor should be size specific.

Reference: Litmanovich DE, Tack DM, Shahrzad M, et al. Dose reduction in cardiothoracic CT: review of currently available methods. Radiographics 2014;34(6):1469-1489. doi: 10.1148/rg.346140084.

8 Answer C. In patients with contraindication to beta-blocker (such as second-degree heart block, severe asthma, decompensated heart failure), a calcium channel blocker can be used. Verapamil is a calcium blocker agent. Atenolol is a beta-blocker so it should not be used if there is contraindication to beta-blocker. Nitroglycerin is used for vasodilatation of the coronaries and will not slow the heart rate. Sildenafil (Viagra) should not be used concurrently with nitroglycerin as it could cause severe hypotension.

Reference: Taylor CM, Blum A, Abbara S. Patient preparation and scanning techniques. Radiol Clin North Am 2010;48(4):675-686. doi: 10.1016/j.rcl.2010.04.011.

9 Answer C. Phase-contrast images are used to measure blood flow and velocity. In cardiac imaging, they are most commonly used to evaluate the peak velocity in cases of valve stenosis and the regurgitant fraction in cases of valve insufficiency. A bipolar gradient is applied, and results in stationary objects experiencing no net phase shift while moving objects will experience a phase shift proportional to their velocity, which yields signal. If the velocity-encoding gradient is set too high or low, aliasing will occur (which is not on the image below).

Reference: Lotz J, et al. Cardiovascular flow measurement “with phase-contrast MR imaging: basic facts and implementation. Radiographics 2002;22(3):651-671.

10 Answer C. With a single-source CT scanner, the image can be generated once 180 degrees of data have been acquired. The temporal resolution is calculated by dividing the rotation speed of the scanner by 2 (Temporal resolution = Rotation speed/2). In our example, 200 msec = Rotation speed/2; 400 msec = Rotation speed.

Reference: Lin E, Alessio A. What are the basic concepts of temporal, contrast, and spatial resolution in cardiac CT. Cardiovasc Comput Tomogr 2009;3(6):403-408.

11 Answer B. Patients with an elevated heart rate who undergo retrospective cardiac CTA can have the data analyzed using multisegment reconstruction techniques. When using multisegment reconstruction, the image will be created using data from multiple heart beats. This will produce an image that potentially has better temporal resolution than single segment reconstruction. Multisegment reconstruction requires the study be acquired with a low pitch. The use of multiple heart beats makes this techniques susceptible to motion artifact and heart rate variability.

Reference: Mahesh M, Cody DD. Physics of cardiac imaging “with multiple-row detector CT. Radiographics 2007;27(5):1495-1509.

12 Answer D. The balanced steady-state free precession sequence is a gradient-echo sequence that is susceptible to metallic artifact and has weighted T2/T1 signal. While the sequence is relatively T2 weighted, it will also have T1 properties.

References: Chavan GB, Babyn PS, Jankharia BG, et al. Steady-state MR imaging sequences: physics, classification, and clinical applications. Radiographics 2008;28(4)1147-1160.

Bieri O, Scheffler K. Fundamentals of balanced steady state free precession MRI. J Magn Reson Imaging 2013;38:2-11. doi: 10.1002/jmri.24163.

13 Answer B. The maximum-intensity projection image uses the maximum voxel value to create a displayed value. The technique is useful to evaluate vessels; however, if the vessel is densely calcified or if there is metallic material, this technique may obscure the vessel lumen.

Reference: Calhoun PS, Kuszyk BS, Heath DG, et al. Three-dimensional volume rendering of spiral CT data: theory and method. Radiographics 1999;19(3):745-764.

14 Answer A. The abnormality most likely occurred on the curved planar-reformatted image. This technique places the long axis of the vessel (i.e., coronary artery) on a single image, allowing it to be visualized along its entire course. It allows stenosis to be readily visualized; however, it is susceptible to pseudolesions from an inability to show the vessel along its true long axis. This can result from unsuccessful vessel extraction, or motion artifact.

Reference: Dalrymple NC, Prasad SR, Freckleton MW, et al. Introduction to the language of three-dimensional imaging with multidetector CT. Radiographics 2005;25(5):1409-1428.

15 Answer D. Temporal Resolution = TR × Views per segment Temporal resolution is determined by how quickly the image is obtained (like shutter speed in a camera). Better temporal resolution is required to visualize fast moving structures such as valve leaflets.

References: Lee VS. Cardiovascular MRI: Physical principles to practical protocols. Lippincott Williams & Wilkins, 2006:291.