Effect of Padding Duration on Radiation Dose and Image Interpretation in Prospectively ECG-Triggered Coronary CT Angiography

AJR Am J Roentgenol. 2010; 194(4):933-937

Labounty TM, Leipsic J, Min JK, Heilbron B, Mancini GB, Lin FY, Earls JP

OBJECTIVES: Prospectively ECG-triggered coronary CT angiography images are acquired during a window in middiastole. Additional surrounding x-ray beam on time, or padding, can be variably set, and the increased padding results in additional available phases for analysis. The purpose of this study was to assess the effect of padding duration on image interpretability and its incident effect on radiation dose.

METHODS: We prospectively evaluated imaging of 886 patients undergoing consecutive prospectively ECG-triggered coronary CT angiographic examinations at three centers and compared the findings in patients stratified by padding duration. We assessed the effect of padding duration on image interpretability and radiation dose.

RESULTS: The mean patient age was 56 +/- 12 years, and 58% of the patients were men. The median heart rate was 55 beats/min (interquartile range, 50-61 beats/min). Padding duration was 0, 1-99, and 100-150 milliseconds for 268, 482, and 136 patients, respectively, with no difference in image interpretability rate between groups (per patient, 98.8%, 97.3%, and 97.1%; per artery, 99.2%, 99.2%, and 99.1%). The groups differed in median radiation dose (2.3 mSv [interquartile range, 1.5-3.2 mSv]; 3.8 mSv [interquartile range, 2.3-4.7 mSv]; 5.5 mSv [interquartile range, 3.8-6.1 mSv]; p < 0.001). Independent of patient and scan parameters, increased padding was associated with greater radiation dose (45% increase per 100-millisecond increase in padding, p < 0.001).

CONCLUSIONS: In a large multicenter study of coronary CT angiography of patients with excellent heart rate control, the use of minimal padding was associated with a substantial reduction in radiation dose with preserved image interpretability. Use of no or reduced padding should be considered in dose-reduction strategies.

PMID: 20308494

3 Responses

  1. Paul Schoenhagen, MD  on March 30th, 2010

    Also read:

    Reduced “padding” of CT imaging lowers radiation dose with same diagnostic utility.
    HeartWire.
    Reed Miller. March 30, 2010.

  2. Jacobo Kirsch, MD  on March 31st, 2010

    More data to support further decreases in radiation using 64-MDCT technology! It should be noted (as the authors mention) that their cohort had a mean HR of 55bpm during imaging (with a 95% percentile of 68bpm).

  3. Rubinshtein  on April 5th, 2010

    I agree with Dr Kirsch! Low heart rate is a requirement for any radiation lowering technique that modified radiation dose during the cardiac cycle. For example, low heart rate yield a greater reduction in radiation dose while using ECG-based tube current modulation (“dose modulation”). However, with prospective triggering, I personally find another reconstruction phase occasionally useful and the 1 mSv difference between techniques perhaps of less clinical importance (remember the “ALARA” principal).

    By the way, estimated dose (in mSv) cannot be calculated for a specific patient, and therefore it is probably more accurate to report mean dose-length product (in mGy x cm) for a given cohort of patients.


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