Dual source CT coronary angiography in severely obese patients: trading off temporal resolution and image noise

Abstract

Objective: To assess in severely obese patients the subjective and objective image quality parameters and to estimate the radiation dose of dual-source computed tomography coronary angiography (CTCA), using 3 different protocols.

Materials and methods: Dual-source CTCA was performed in 60 patients (30 women; mean age 58 +/- 7 years) suffering from obesity class II or higher (body mass index [BMI] >35 kg/sq m). Twenty patients were examined with a standard CTCA protocol at 120 kV/350 mAs (protocol A), 20 patients with a CTCA protocol at 140 kV/350 mAs (protocol B), and 20 patients at 140 kV/350 mAs with a dedicated obesity protocol (protocol C), that allows the additional data sampling by expanding the data acquisition for each tube from a quarter to a half rotation, permitting to trade off temporal resolution and image noise. Two blinded observers independently assessed the image quality of each coronary segment, using a 4-point scale (1: excellent-4: nondiagnostic) and measured the different image parameters (image noise, signal-to-noise ratio [SNR], and contrast-to-noise ratio [CNR]). Radiation dose estimates were calculated.

Results: The average BMI was 46.3 +/- 8.3 kg/sq m (range, 36.8-69.6 kg/sq m). Subjective image quality (1.55 +/- 0.73) was significantly better in protocol C when compared with protocol A (2.46 +/- 0.76; P < 0.01) and protocol B (2.12 +/- 0.87; P < 0.017). There was a significantly lower rate of coronary artery segments with nondiagnostic image quality when using the obesity protocol C (1.5%; 4/262) compared with that obtained when using protocol A (7.8%; 22/280; P < 0.01) and protocol B (4.4%; 12/275; P < 0.017). Image noise was significantly lower in protocol C (31.8 +/- 5.0 HU) when compared with group A (43.5 +/- 4.7 HU; P < 0.001) and B (36.8 +/- 5.5 HU; P < 0.01). SNR and CNR were significantly higher in group C (13.8 +/- 2.4 and 23.1 +/- 2.8) compared with group A (10.6 +/- 1.7 and 15.1 +/- 3.2; each P < 0.001) and group B (12.0 +/- 2.0 and 18.8 +/- 3.1; each P < 0.01). The estimated effective radiation dose of the obesity protocol C (15.6 +/- 0.9 mSv) was significantly higher when compared with that in protocol A (10.1 +/- 0.8 mSv; P < 0.01), but not significantly different from that in protocol B (13.3 +/- 0.8 mSv; P = 0.022).

Conclusions: Use of an obesity protocol in dual-source CTCA in severely obese patients significantly improves image quality, but goes along with a higher radiation dose.