https://ccme.osu.edu/RSSeriesBrochure/23233%20-%20.pdf

Computed tomographic angiography characteristics of atherosclerotic plaques subsequently resulting in acute coronary syndrome.

Context Cardiac computed tomography (CT) angiography (CCTA) has emerged as a useful diagnostic imaging modality in the assessment of coronary artery disease. However, the potential risks due to exposure to ionizing radiation associated with CCTA have raised concerns. Objectives To estimate the radiation dose of CCTA in routine clinical practice as well as the association of currently available strategies with dose reduction and to identify the independent factors contributing to radiation dose. Design, Setting, and Patients A cross-sectional, international, multicenter, observational study (50 study sites: 21 university hospitals and 29 community hospitals) of estimated radiation dose in 1965 patients undergoing CCTA between February and December 2007. Linear regression analysis was used to identify independent predictors associated with dose. Main Outcome Measure Dose-length product (DLP) of CCTA. Results The median DLP of 1965 CCTA examinations performed at 50 study sites was 885 mGy × cm (interquartile range, 568-1259 mGy × cm), which corresponds to an estimated radiation dose of 12 mSv (or 1.2 × the dose of an abdominal CT study or 600 chest x-rays). A high variability in DLP was observed between study sites (range of median DLPs per site, 331-2146 mGy × cm). Independent factors associated with radiation dose were patient weight (relative effect on DLP, 5%; 95% confidence interval [CI], 4%-6%), absence of stable sinus rhythm (10%; 95% CI, 2%-19%), scan length (5%; 95% CI, 4%-6%), electrocardiographically controlled tube current modulation (−25%; 95% CI, −23% to −28%; applied in 73% of patients), 100-kV tube voltage (−46%; 95% CI, −42% to −51%; applied in 5% of patients), sequential scanning (−78%; 95% CI, −77% to −79%; applied in 6% of patients), experience in cardiac CT (−1%; 95% CI, −1% to 0%), number of CCTAs per month (0%; 95% CI, 0%-1%), and type of 64-slice CT system (for highest vs lowest dose system, 97%; 95% CI, 88%-106%). Algorithms for dose reduction were not associated with deteriorated diagnostic image quality in this observational study. Conclusions Median doses of CCTA differ significantly between study sites and CT systems. Effective strategies to reduce radiation dose are available but some strategies are not frequently used. The comparable diagnostic image quality may support an increased use of dose-saving strategies in adequately selected patients.

https://jamanetwork.com/journals/jama/articlepdf/183324/joc90001_500_507.pdf

Estimated Radiation Dose Associated With Cardiac CT Angiography

Context Cardiac computed tomography (CT) angiography (CCTA) has emerged as a useful diagnostic imaging modality in the assessment of coronary artery disease. However, the potential risks due to exposure to ionizing radiation associated with CCTA have raised concerns. Objectives To estimate the radiation dose of CCTA in routine clinical practice as well as the association of currently available strategies with dose reduction and to identify the independent factors contributing to radiation dose. Design, Setting, and Patients A cross-sectional, international, multicenter, observational study (50 study sites: 21 university hospitals and 29 community hospitals) of estimated radiation dose in 1965 patients undergoing CCTA between February and December 2007. Linear regression analysis was used to identify independent predictors associated with dose. Main Outcome Measure Dose-length product (DLP) of CCTA. Results The median DLP of 1965 CCTA examinations performed at 50 study sites was 885 mGy × cm (interquartile range, 568-1259 mGy × cm), which corresponds to an estimated radiation dose of 12 mSv (or 1.2 x the dose of an abdominal CT study or 600 chest x-rays). A high variability in DLP was observed between study sites (range of median DLPs per site, 331-2146 mGy x cm). Independent factors associated with radiation dose were patient weight (relative effect on DLP, 5%; 95% confidence interval [Cl], 4%-6%), absence of stable sinus rhythm (10%; 95% Cl, 2%-19%), scan length (5%; 95% Cl, 4%-6%), electrocardiographically controlled tube current modulation (-25%; 95% Cl, -23% to -28%; applied in 73% of patients), 100-kV tube voltage (-46%; 95% Cl, -42% to -51 %; applied in 5% of patients), sequential scanning (-78%; 95% Cl, -77% to -79%; applied in 6% of patients), experience in cardiac CT (-1%; 95% Cl, -1 % to 0%), number of CCTAs per month (0%; 95% Cl, 0%-1 %), and type of 64-slice CT system (for highest vs lowest dose system, 97%; 95% Cl, 88%-106%). Algorithms for dose reduction were not associated with deteriorated diagnostic image quality in this observational study. Conclusions Median doses of CCTA differ significantly between study sites and CT systems. Effective strategies to reduce radiation dose are available but some strategies are not frequently used. The comparable diagnostic image quality may support an increased use of dose-saving strategies in adequately selected patients.

Estimated Radiation Dose Associated With Cardiac CT Angiography. Commentary

Aims We evaluated the feasibility and image quality of a new scan mode for coronary computed tomography angiography (CTA) with an effective dose of less than 1 mSv.

Methods and results In 50 consecutive patients (body weight ≤ 100 kg, sinus rhythm ≤60 b.p.m. after pre-medication, coronary CTA was performed using a dual-source CT system with 2 × 128 × 0.6 mm collimation, 0.28 s rotation time, a pitch of 3.2 or 3.4, 100 kV tube voltage and current of 320 mA s. Data acquisition was prospectively triggered at 60% of the R–R interval and completed within one cardiac cycle. Image quality was evaluated using a four-point scale (1 = absence of any artefacts to 4 = uninterpretable). In all 50 patients, imaging was successful. Mean duration of data acquisition was 258 ± 20 ms. Mean dose-length product was 62 ± 5 mGy cm, the effective dose was 0.87 ± 0.07 mSv (0.78–0.99 mSv). Of the 742 coronary artery segments, 94% had an image quality score of 1, 5.0% a score of 2, 0.9% a score of 3, and 4 segments (0.5%) were ‘uninterpretable’.

Conclusion In non-obese patients with a low and stable heart rate, prospectively ECG-triggered high-pitch spiral coronary CTA provides excellent image quality at a consistent dose below 1.0 mSv.

Coronary computed tomography angiography with a consistent dose below 1 mSv using prospectively electrocardiogram-triggered high-pitch spiral acquisition

Purpose To evaluate image quality and contrast opacification from coronary images acquired from 320-detector row computed tomography (CT). Patient dose is estimated for prospective and retrospective ECG-gating; initial correlation between 320-slice CT and coronary catheterization is illustrated. Methods Retrospective image evaluation from forty consecutive patients included subjective assessment of image quality and contrast opacification (80 ml iopamidol 370 mg I/ml followed by 40 ml saline). Region of interest opacification measurements at the ostium and at 2.5 mm diameter were used to determine the gradient of contrast opacification (defined as the proximal minus distal HU measurements) in coronary arteries imaged in a single heartbeat. Estimated effective dose was compared for prospective versus retrospective ECG-gating, two body mass index categories (30 kg/m2 cutoff), and single versus two heartbeat acquisition. When available, CT findings were correlated with those from coronary catheterization. Results Over 89% of arterial segments (15 segment model) had excellent image quality. The most common reason for image degradation was cardiac motion. One segment in one patient was considered unevaluable. Contrast opacification was almost universally considered excellent. The mean Hounsfield units (HU) was greater than 350; the coronary contrast opacification gradient was 30–50 HU. Patient doses were greater for retrospective ECG-gating, larger patients, and those imaged with two heartbeats. For the most common (n = 25) protocol (120 kV, 400 mA, prospective ECG-gating, 60–100% phase window, 16 cm craniocaudal coverage, single heartbeat), the mean dose was 6.8 ± 1.4 mSv. All CT findings were confirmed in the four patients who underwent coronary catheterization. Conclusion Initial 320-detector row coronary CT images have consistently excellent quality and iodinated contrast opacification. These patients were scanned with conservative protocols with respect to iodine load, prospective ECG-gating phase window, and craniocaudal coverage. Future work will focus on lowering contrast and radiation dose while maintaining image quality.

Initial evaluation of coronary images from 320-detector row computed tomography

Aims To determine the feasibility of prospective electrocardiogram (ECG)-gating to achieve low-dose computed tomography coronary angiography (CTCA).

Methods and results Forty-one consecutive patients with suspected ( n = 35) or known coronary artery disease ( n = 6) underwent 64-slice CTCA using prospective ECG-gating. Individual radiation dose exposure was estimated from the dose-length product. Two independent readers semi-quantitatively assessed the overall image quality on a five-point scale and measured vessel attenuation in each coronary segment. One patient was excluded for atrial fibrillation. Mean effective radiation dose was 2.1 ± 0.6 mSv (range, 1.1–3.0 mSv). Image quality was inversely related to heart rate (HR) (57.3 ± 6.2, range 39–66 b.p.m.; r = 0.58, P 63 b.p.m. ( P < 0.001).

Conclusion This first experience documents the feasibility of prospective ECG-gating for CTCA with diagnostic image quality at a low radiation dose (1.1–3.0 mSv), favouring HR <63 b.p.m.

http://www.rodiag.ch/documents/download/ehj2008%20prosp%20gating%20feasibility.pdf

Feasibility of low-dose coronary CT angiography: first experience with prospective ECG-gating

In a 66-year-old patient with prolonged episodes of chest pain, catheter angiography revealed total occlusions of the right coronary artery and the distal circumflex artery (CX) as well as 2 sequential significant stenoses in the proximal CX and one significant stenosis in the proximal left anterior descending artery (LAD). To identify the culprit lesions with their respective territory, noninvasive assessment of viability was performed by F-18 FDG positron emission tomography (PET) and fused with a low-dose computed tomography coronary angiography using prospective electrocardiogram gating. Fused PET/computed tomography coronary angiography images demonstrated a large scar in the inferior myocardium, corresponding to the total occlusion in the right coronary artery, viable myocardium in the territory of the CX, and infarcted scar tissue with partially preserved viability in the anterior myocardium, corresponding to the presumably recanalized lesion in the LAD. The patient was scheduled for revascularization of the lesions in the LAD and the CX to reverse dysfunctional but viable myocardial segments.

https://www.zora.uzh.ch/id/eprint/11859/1/document.pdf

Cardiac fusion imaging with low-dose computed tomography using prospective electrocardiogram gating.

With the development of new technologies, computed tomography (CT) is becoming a strong candidate for non-invasive imaging based tool for cardiac disease assessment. One of the challenges of cardiac CT is that a typical scan involves a breath hold period consisting of several heartbeats, about 20 sec with scanners having a longitudinal coverage of 2 cm, and causing the image quality (IQ) to be negatively impacted since beat to beat variation is high likely to occur without any medication, e.g. beta blockers. Because of this and the preference for shorter breath hold durations, a CT scanner with a wide coverage without the compromise in the spatial and temporal resolution of great clinical value. In this study, we aimed at determining the optimum scan duration and the delay relative to beginning of breath hold, to achieve high IQ. We acquired EKG data from 91 consecutive patients (77 M, 14 F; Age: 57 ± 14) undergoing cardiac CT exams with contrast, performed on LightSpeed 16 and LightSpeed Pro 16 . As an IQ metric, we adopted the standard deviation of "beat-to-beat variation" (stdBBV) within a virtual scan period. Two radiologists evaluated images by assigning a score of 1 (worst) to 4 best). We validated stdBBV with the radiologist scores, which resulted in a population distribution of 9.5, 9.5, 31, and 50% for the score groups 1, 2, 3, and 4, respectively. Based on the scores, we defined a threshold for stdBBV and identified an optimum combination of virtual scan period and a delay. With the assumption that the relationship between the stdBBV and diagnosable scan IQ holds, our analysis suggested that the success rate can be improved to 100% with scan durations equal or less than 5 sec with a delay of 1 - 2 sec. We confirmed the suggested conclusion with LightSpeed VCT (GE Healthcare Technologies, Waukesha, WI), which has a wide longitudinal coverage, fine isotropic spatial resolution, and high temporal resolution, e.g. 40 mm coverage per rotation of 0.35 sec. Under the light of this study, LightSpeed VCT lends itself to be a clinically tested unique platform to achieve routine cardiac imaging.

Wide coverage by volume CT: benefits for cardiac imaging

We present the results of dose and image quality performance evaluation of a novel, prospective ECG-gated Coronary CT Angiography acquisition mode (SnapShot Pulse, LightSpeed VCT-XT scanner, GE Healthcare, Waukesha, WI), and compare it to conventional retrospective ECG gated helical acquisition in clinical and phantom studies. Image quality phantoms were used to measure noise, slice sensitivity profile, in-plane resolution, low contrast detectability and dose, using the two acquisition modes. Clinical image quality and diagnostic confidence were evaluated in a study of 31 patients scanned with the two acquisition modes. Radiation dose reduction in clinical practice was evaluated by tracking 120 consecutive patients scanned with the prospectively gated scan mode. In the phantom measurements, the prospectively gated mode resulted in equivalent or better image quality measures at dose reductions of up to 89% compared to non-ECG modulated conventional helical scans. In the clinical study, image quality was rated excellent by expert radiologist reviewing the cases, with pathology being identical using the two acquisition modes. The average dose to patients in the clinical practice study was 5.6 mSv, representing 50% reduction compared to a similar patient population scanned with the conventional helical mode.

Olivier Adda

Papers

Feasibility of low-dose coronary CT angiography: first experience with prospective ECG-gating

Cardiac fusion imaging with low-dose computed tomography using prospective electrocardiogram gating.

Wide coverage by volume CT: benefits for cardiac imaging

Dose reduction of up to 89% while maintaining image quality in cardiovascular CT achieved with prospective ECG gating