Abstract
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.
Highlights
The radiation dose decreased with every technical advance from filtered back projection (FBP) to iterative reconstruction (IR) and further with IR/integrated circuit detector (ICD) [Table 1]
A further decline in the radiation dose was observed with the combination of IR and ICD: Dose-length product (DLP) was 167.5 mGy*cm ± 54.5 (IR vs. IR/ICD: P
Corresponding with the reduction in the DLP, the CTDI Vol decreased from 7.8 ± 2.5 (FBP) to 5.4 ± 2.0 (IR) and to 4.5 ± 1.5 (IR/ICD)
Summary
Since the introduction of computed tomography (CT) in clinical practice in the late 1970s, dose reduction has been a major concern for radiologists and their patients.[1,2] Over the last few decades, spiral CT, cardiac imaging, perfusion techniques, high-pitch CT, and dual-energy CT have been introduced to clinical practice, increasing the overall amount of radiation applied.[3,4] In contrast, a multitude of dose reduction methods have been developed on the hardware side, such as dose modulation along the x-, y-, and z-axes.[5,6,7,8] Shielding[9,10,11,12,13,14] demonstrates a further major step in manufacturer-dependent radiation protection. IR has the potential to lower the amount of radiation applied significantly and to maintain the radiation at a constant minimum.[15,16] The introduction of the most recent fully integrated circuit detector (ICD) geometry, realized in the Stellar detectors by Siemens (Erlangen, Germany), demonstrated initial promising potential to reduce the radiation further[17] by minimizing electronic noise. A major concern in dose reduction has been the preservation of diagnostic image quality, measured by noise, the signal-to-noise ratio (SNR), and the contrast-to-noise ratio (CNR).[18,19,20] The previous data have suggested that diagnostic image quality could be maintained while concurrently lowering the radiation dose, by adopting the recent technologies mentioned above.[21,22] We hypothesized that the current implementation of an iterative algorithm and the launch of the ICD geometry would result in a sustainable dose reduction that would preserve the diagnostic image quality. We compared 150 standard chest CTs, from clinical routines that were acquired with the standard Siemens scan parameter presettings, with an intravenous contrast application on a Siemens Sensation scanner with filtered back projection (FBP), the most recent Siemens Definition Flash scanner with IR and the Siemens Edge CT scanner, which was equipped with IR and ICD
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