Abstract
PurposeTo compare CT pulmonary angiographies (CTPAs) as well as phantom scans obtained at 100 kVp with a conventional CT (C-CT) to virtual monochromatic images (VMI) obtained with a spectral detector CT (SD-CT) at equivalent dose levels as well as to compare the radiation exposure of both systems. Material and MethodsIn total, 2110 patients with suspected pulmonary embolism (PE) were examined with both systems. For each system (C-CT and SD-CT), imaging data of 30 patients with the same mean CT dose index (4.85 mGy) was used for the reader study. C-CT was performed with 100 kVp and SD-CT was performed with 120 kVp; for SD-CT, virtual monochromatic images (VMI) with 40, 60 and 70 keV were calculated. All datasets were evaluated by three blinded radiologists regarding image quality, diagnostic confidence and diagnostic performance (sensitivity, specificity). Contrast-to-noise ratio (CNR) for different iodine concentrations was evaluated in a phantom study. ResultsCNR was significantly higher with VMI at 40 keV compared to all other datasets. Subjective image quality as well as sensitivity and specificity showed the highest values with VMI at 60 keV and 70 keV. Hereby, a significant difference to 100 kVp (C-CT) was found for image quality. The highest sensitivity was found using VMI at 60 keV with a sensitivity of more than 97 % for all localizations of PE. For diagnostic confidence and subjective contrast, highest values were found with VMI at 40 keV. ConclusionHigher levels of diagnostic performance and image quality were achieved for CPTAs with SD-CT compared to C-CT given similar dose levels. In the clinical setting SD-CT may be the modality of choice as additional spectral information can be obtained.
Highlights
Computed tomography (CT) is a standard imaging modality with a high importance in various clinical fields
Two different energy spectra are used for the Abbreviations: BMI, body mass index; Contrast-to-noise ratio (CNR), contrast-to-noise ratio; CT, computed tomography; conventional CT (C-CT), conventional spiral CT; CTDIVOL, volume-weighted CT dose index; CTPA, CT pulmonary angiography; dual-energy CT (DE-CT), dual-Energy CT; dual-source CT (DS-CT), dual-Source CT; DLP, dose length product; ED, effective dose; IQ, image quality; keV, kiloelectronvolt; kVp, peak kilovoltage; HU, Hounsfield Units; PE, pulmonary embolism; Regions of interest (ROI), region of interest; spectral detector CT (SD-CT), spectral-detector CT; VMI, virtual monochromatic images
CNR in the phantom study was significantly higher in monoE-40 compared to other VMI and to C-CT (Table 2)
Summary
Computed tomography (CT) is a standard imaging modality with a high importance in various clinical fields. All routinely used contrast agents for CT diagnostics contain iodine as the attenuating material [1]. Iodine cannot be directly differentiated or quantified with conventional CT systems [2] This drawback has been overcome by dual-energy CT (DE-CT) [3]. With these systems, two different energy spectra are used for the Abbreviations: BMI, body mass index; CNR, contrast-to-noise ratio; CT, computed tomography; C-CT, conventional spiral CT; CTDIVOL, volume-weighted CT dose index; CTPA, CT pulmonary angiography; DE-CT, dual-Energy CT; DS-CT, dual-Source CT; DLP, dose length product; ED, effective dose; IQ, image quality; keV, kiloelectronvolt; kVp, peak kilovoltage; HU, Hounsfield Units; PE, pulmonary embolism; ROI, region of interest; SD-CT, spectral-detector CT; VMI, virtual monochromatic images
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