[Low dose cardiac computed tomography: how to obtain it?]

[Cardiac CT-Scan: Utility for the management of chest pain, cardiovascular screening and before atrial fibrillation ablation procedure]

Cardiac CT-scan is recommended for sorting patients presenting with stable or acute chest pain with low to intermediate risk of coronary artery disease (CAD). Recent studies have shown its reliability for diagnosing CAD in high-risk patients, notably those with acute coronary syndrome (ACS) without ST-elevation. Coronary CT-scan also represents a great opportunity for the screening of atherosclerosis in patients at risk and allows a better prevention of coronary artery disease by introduction of preventive treatments in patients with abnormal coronary CT-scan, especially statins. It is useful for the follow-up of patients who underwent a coronary arteries revascularization with either stents or bypasses. Coronary arteries calcium scoring appears to be an independent predictive factor of cardiovascular and total mortality and its use is recommended for stratifying the cardiovascular risk. However, its interpretation remains unobvious and the patient management is poorly improved by the results. Anyway, if the score is above zero, atherosclerosis is present and therefore a lipid lowering treatment should be discussed. Cardiac CT-scan has become the Gold Standard exam before an aortic valve replacement, for the measurement of the aortic root notably, allowing the best prothesis selection. Before atrial fibrillation ablation procedure by pulmonary vein isolation, the cardiac CT-scan allows a 3-D visualization of the two atria, especially the left atrium, and rules out any suspicion of cardiac thrombus. It allows the research of an anomalous pulmonary venous connection. The 3-D support will also enable the operator to navigate in the heart during the ablation procedure.

Establishment of diagnostic reference levels in cardiac CT in France: a need for patient dose optimisation

The objective of this study was to propose diagnostic reference levels (DRLs) for coronary computed tomography angiography (CCTA), in the context of a large variability in patient radiation dose, and the lack of European recommendations. Volume Computed Tomography Dose Index (CTDIvol) and dose-length product (DLP) were collected from 460 CCTAs performed over a 3-month period at eight French hospitals. CCTAs (∼50 per centre) were performed using the routine protocols of the centres, and 64- to 320-detector CT scanners. ECG gating was prospective (n = 199) or retrospective (n = 261). The large gap in dose between these two modes required to propose specific DRLs: 26 and 44 mGy for CTDIvol, and 370 and 970 mGy cm for DLP, respectively. This study confirms the large variability in patient doses during CCTA and underlines the need for the optimisation of cardiac acquisition protocols. Availability of national DRLs should be mandatory in this setting.

Feasible Dose Reduction in Routine Chest Computed Tomography Maintaining Constant Image Quality Using the Last Three Scanner Generations: From Filtered Back Projection to Sinogram-affirmed Iterative Reconstruction and Impact of the Novel Fully Integrated Detector Design Minimizing Electronic Noise

Objective:

The aim of the present study was to evaluate a dose reduction in contrast-enhanced chest computed tomography (CT) by comparing the three latest generations of Siemens CT scanners used in clinical practice. We analyzed the amount of radiation used with filtered back projection (FBP) and an iterative reconstruction (IR) algorithm to yield the same image quality. Furthermore, the influence on the radiation dose of the most recent integrated circuit detector (ICD; Stellar detector, Siemens Healthcare, Erlangen, Germany) was investigated.

Materials and Methods:

136 Patients were included. Scan parameters were set to a thorax routine: SOMATOM Sensation 64 (FBP), SOMATOM Definition Flash (IR), and SOMATOM Definition Edge (ICD and IR). Tube current was set constantly to the reference level of 100 mA automated tube current modulation using reference milliamperes. Care kV was used on the Flash and Edge scanner, while tube potential was individually selected between 100 and 140 kVp by the medical technologists at the SOMATOM Sensation. Quality assessment was performed on soft-tissue kernel reconstruction. Dose was represented by the dose length product.

Results:

Dose-length product (DLP) with FBP for the average chest CT was 308 mGy*cm ± 99.6. In contrast, the DLP for the chest CT with IR algorithm was 196.8 mGy*cm ± 68.8 (P = 0.0001). Further decline in dose can be noted with IR and the ICD: DLP: 166.4 mGy*cm ± 54.5 (P = 0.033). The dose reduction compared to FBP was 36.1% with IR and 45.6% with IR/ICD. Signal-to-noise ratio (SNR) was favorable in the aorta, bone, and soft tissue for IR/ICD in combination compared to FBP (the P values ranged from 0.003 to 0.048). Overall contrast-to-noise ratio (CNR) improved with declining DLP.

Conclusion:

The most recent technical developments, namely IR in combination with integrated circuit detectors, can significantly lower radiation dose in chest CT examinations.