The Heart: Part 1 (pretest)

1. Studies have shown the diagnostic accuracy of coronary CTA is decreased in patients with:

Tachycardia

BMI >30kg/m2

Calcium score >400

All of the above

Diagnostic accuracy of Cardiac CT is decreased with high heart rates (particularly > 70bpm), BMI >30 and high calcium scores

Explanation

Diagnostic accuracy of Cardiac CT is decreased with high heart rates (particularly > 70bpm), BMI >30 and high calcium scores

2. Which of the following organs generally receives the greatest radiation dose during Cardiac CT?

Stomach

Breast

Heart

Esophagus

The breast and skin receive highest radiation dose. Breast shields lower dose but increase image noise.

Explanation

The breast and skin receive highest radiation dose. Breast shields lower dose but increase image noise.

3. For which patient would coronary CTA NOT be appropriate?

Patients admitted for a ST elevation MI and have positive Troponin

Patients with borderiine or equivocal positive stress tests

Patient with atypical chest pain, a LBBB of unknown duration, with normal serial cardiac enzymes

Patients who are admitted to rule out MI, with negative biomarkers (negative Troponin)

Coronary CTA (Computed Tomography Angiography) is not appropriate for patients admitted for a ST elevation MI (Myocardial Infarction) and have positive Troponin because these patients require immediate intervention and treatment rather than a diagnostic imaging test. ST elevation MI indicates a complete blockage of a coronary artery, which requires urgent reperfusion therapy such as angioplasty or thrombolytic therapy. Positive Troponin levels confirm myocardial damage, further emphasizing the need for immediate treatment. Coronary CTA is not suitable in this scenario as it would cause unnecessary delay in providing the necessary medical intervention.

Explanation

Coronary CTA (Computed Tomography Angiography) is not appropriate for patients admitted for a ST elevation MI (Myocardial Infarction) and have positive Troponin because these patients require immediate intervention and treatment rather than a diagnostic imaging test. ST elevation MI indicates a complete blockage of a coronary artery, which requires urgent reperfusion therapy such as angioplasty or thrombolytic therapy. Positive Troponin levels confirm myocardial damage, further emphasizing the need for immediate treatment. Coronary CTA is not suitable in this scenario as it would cause unnecessary delay in providing the necessary medical intervention.

4. When performing a "triple rule out" protocol, the simultaneous opacification of the coronary arteries, thoracic aorta, and pulmonary arteries requires which of the following?

Faster contrast injection

Larger contrast volume

Higher tube current

Thinner slice collimation

To simultaneously opacify the coronary arteries, aorta and pulmonary arteries, the duration of the contrast injection must be longer which will result in a larger volume of contrast. This is due to longer z-axis and contrast opacification in the pulmonary arteries must be maintained at the same time as the aorta. The scan also requires a longer breathhold. Rate of contrast injection, tube current and slice collimation are unchanged.

Explanation

To simultaneously opacify the coronary arteries, aorta and pulmonary arteries, the duration of the contrast injection must be longer which will result in a larger volume of contrast. This is due to longer z-axis and contrast opacification in the pulmonary arteries must be maintained at the same time as the aorta. The scan also requires a longer breathhold. Rate of contrast injection, tube current and slice collimation are unchanged.

5. A major reason why thin collimation and thin slice reconstruction are required for coronary CTA is to:

Increase scan coverage

Minimize radiation dose

Obtain adequate temporal resolution

Achieve high z-axis resolution and avoid volume averaging

In coronary CT angiography, the imaging target is a small structure (

Explanation

In coronary CT angiography, the imaging target is a small structure (

6. Which of the following options will lead to the greatest reduction in radiations exposure to the patient?

Decreasing peak tube voltage from 120 to 100 kVp

Decreasing tube current from 500 to 400 mAs

Increasing collimation from 64 x 0.5 to 32 x 1mm

Decreasing pitch from 0.3 to 0.2

The change in radiation is proportional to the square of the peak tube voltage, while it is proportional to the changeof tube current. Increasing slice thickness will help reduce radiation dose but to a smaller degree. Decreasing the pitch will increase the radiation dose, because there is more overlap/oversampling.

Explanation

The change in radiation is proportional to the square of the peak tube voltage, while it is proportional to the changeof tube current. Increasing slice thickness will help reduce radiation dose but to a smaller degree. Decreasing the pitch will increase the radiation dose, because there is more overlap/oversampling.

7. Which of the following factors does not influence the number of photons which contribute to a reconstructed slice?

Tube current

Scan time

Reconstructed slice width

Reconstruction kernel

Tube current, scan time and reconstruction slice width all influence the number of photons which contribute to the reconstruction of a single slice whereas reconstruction kernel selection is a post processing technique used to display the data.

Explanation

Tube current, scan time and reconstruction slice width all influence the number of photons which contribute to the reconstruction of a single slice whereas reconstruction kernel selection is a post processing technique used to display the data.

8. An advantage of performing a coronary CT angiogram with retrospectively ECG-gated CT compared to prospective ECG-triggered CT includes all EXCEPT:

The ability to reconstruct overlapping slices for increased z-axis resolution.

Considerably less radiation exposure.

Ability to calculate ejection fraction.

Arrhythmias are less likely to cause image artifacts.

Prospective ECG triggered exams are associated with significantly reduced radiation (up to 80%) compared to retrospective acquisition.

Explanation

Prospective ECG triggered exams are associated with significantly reduced radiation (up to 80%) compared to retrospective acquisition.

9. A 44 year-old man with chest pain and equivocal stress ECG test arrives for Cardiac CTA. His Calcium score is 400. The patient has a history of bronchospasm and daily use of bronchodilator. His heart rate at check-in is 88 bpm. How do you proceed?

Perform scan without beta-blocker using retrospective gating

Use a short-acting IV metoprolol immediately prior to scan

Use a long-acting oral metoprolol one hour before the scan

Cancel the study and consider alternative diagnostic test

A beta blocker (IV or oral) should not be used in patients with a history of severe bronchospasm.

Explanation

A beta blocker (IV or oral) should not be used in patients with a history of severe bronchospasm.

10. Regarding data acquisition in axial (prospective) and helical (retrospective) scanning modes, which of the following statements is correct?

In axial scanning mode, each detector row is dedicated to one z-axis slice per gantry rotation

In axial scanning mode, each detector row is dedicated to multiple z-axis slice levels per gantry rotation

In helical scanning mode, each detector row is dedicated to one z-axis slice level per gantry rotation

In axial scanning (used in prospective gating) the table does not move during scan acquisition and patient is fed through in a stepwise manner thus each detectors remains dedicated to one z axis level . In helical scanning (with retrospective gating) there is contnuous movement during acquisition therefore each detector row acquires data from multiple slice levels throughout the scan and reconstructed by interpolation.

Explanation

In axial scanning (used in prospective gating) the table does not move during scan acquisition and patient is fed through in a stepwise manner thus each detectors remains dedicated to one z axis level . In helical scanning (with retrospective gating) there is contnuous movement during acquisition therefore each detector row acquires data from multiple slice levels throughout the scan and reconstructed by interpolation.

11. A patient taking sildenafil (Viagra) for erectile dysfunction took the medication two days ago. He presents for a cardiac CTA for atypical chest pain, what is the most appropriate action?

Proceed with scan without sublingual nitroglycerin

Proceed with the scan with sublingual nitroglycerin

Reschedule his test for next day

Consider alternate testing

Nitroglycerin should not be used if sildenafil is taken in the past 24 hours. The half-life of sildenafil is 4-5h therefore, is cleared by 24h.

Explanation

Nitroglycerin should not be used if sildenafil is taken in the past 24 hours. The half-life of sildenafil is 4-5h therefore, is cleared by 24h.

12. Which of the following should be considered in preparation for a cardiac CT scan to assess for anomalous coronary artery origin in a 32 year woman with a heart rate of 86 bpm despite beta-blocker administration?

Increase pitch from 0.2 to 0.4

Prospective ECG-triggering instead of retrospective ECG-gating

Dual source CT and retrospective ECG-gating

MRI examination

Young women are at higher risk from radiation induced cancer from cardiac CT, while using a low-dose rpospective ECG triggered exam with new technology scanners, the proximal coronaries can frequently be visualized with MRI.

Explanation

Young women are at higher risk from radiation induced cancer from cardiac CT, while using a low-dose rpospective ECG triggered exam with new technology scanners, the proximal coronaries can frequently be visualized with MRI.

The Heart: Part 1 (Pretest)