Cardiology>>>>>CT, CMR, And Nuclear Imaging
Question 4#

Concerning ionizing radiation in cardiac CT, which one of the following statements is true?

a. Cardiac CT is always performed in >2 mSv
b. A patient with a low BMI will have a higher radiation dose
c. Reducing the kilovoltage will reduce the radiation dose
d. Prospective ECG gating gives a higher dose to the patient than retrospective ECG gating
e. Calcium scoring has a higher radiation dose than coronary CT angiography

Correct Answer is C

Comment:

Historically, cardiac CT has been recognized as a high-radiation investigation and this has been cited as an adverse reason for considering its routine use. Whilst the dose can be high, careful optimization of scanning parameters with aggressive ECG-gated dose-modulation techniques can result in cardiac CT being performed with a dose of <1 mSv.

Calcium scoring is a relatively low-dose study (currently <0.5 mSv) and is lower than a CT coronary angiogram.

Techniques to limit the radiation dose include reducing the kilovoltage (dose is proportional to kV2 ) and limiting the scanned field of view. Prospective gating, in which the scan is limited to a fixed segment of the cardiac cycle (usually mid to late diastole), will also reduce the radiation dose compared with retrospective scanning, which acquires data (and therefore administers radiation) throughout the cardiac cycle. If a retrospective method of scanning is used, the dose can be minimized by using of ECG-gated dose modulation, with only a fraction of the maximal tube current (e.g. 4% or 20%) administered outside the useful diastolic reconstruction window.

The dose administered will increase with increasing BMI, as a higher kilovoltage (kV) and tube current (mA s) are required to penetrate an increased depth of tissue and maintain an adequate signal-to-noise ratio (good image quality).