Assessment of pulmonary perfusion with breath-hold and free-breathing dynamic contrast-enhanced magnetic resonance imaging: quantification and reproducibility

Abstract Objectives: The purpose of this study was to investigate whether quantification of pulmonary perfusion from dynamic contrast-enhanced (DCE) MRI yields more reproducible results with data acquired during free breathing than with data from conventional breath-hold measurements. Material and Methods: 10 healthy male volunteers underwent two imaging sessions at a clinical 1.5T-MRI system, separated by a week ± one day. Each of these sessions comprised two DCE MRI acquisitions, one performed during breath-hold, and one during free, shallow breathing; both acquisitions were separated by at least 20 minutes. For all DCE MRI measurements, a standard dose of Gadobutrol was used. Breath hold measurements lasted 53 seconds; free-breathing acquisitions were performed in a total acquisition time of 146 seconds. Lung tissue was segmented automatically to minimize user influence and pulmonary plasma flow (PPF) and volume (PPV) were quantified on a perpixel basis with a one-compartment model. Freebreathing measurements were analyzed twice, (a) including data from the entire acquisition duration and (b) after truncation to the duration of the breath-hold measurements. For further statistical analysis, median values of the resulting parameter maps were determined. To assess intra-individual reproducibility, intra-class correlation coefficients and coefficients of variation between first and second measurements were calculated for breathhold, truncated and full free-breathing measurements, respectively. Differences in the coefficients of variation were assessed with a non-parametric two-sided paired Wilcoxon signed-rank test. Results: All 40 measurements were completed successfully. Maps of PPF and PPV could be calculated from both measurement techniques; PPF and PPV in the breath-hold measurements were significantly lower (p<0.001) than in truncated and full free-breathing measurements. Both evaluations of the free-breathing measurements yielded higher intra-class correlation coefficients and lower coefficients of variation between first and second measurements than in the breath-hold measurements. Conclusions: Besides offering substantially higher patient comfort, free-breathing DCE MRI acquisitions allow for pixel-wise quantification of pulmonary perfusion and hence generation of parameter maps. Moreover, quantitative perfusion estimates derived from free-breathing DCE MRI measurements have better reproducibility than estimates from the conventionally used breath-hold measurements

How Low Can We Go in Contrast-Enhanced CT Imaging of the Chest?: A Dose-Finding Cadaver Study Using the Model-based Iterative Image Reconstruction Approach.

RATIONALE AND OBJECTIVES: Dose reduction may compromise patients because of a decrease of image quality. Therefore, the amount of dose savings in new dose-reduction techniques needs to be thoroughly assessed. To avoid repeated studies in one patient, chest computed tomography (CT) scans with different dose levels were performed in corpses comparing model-based iterative reconstruction (MBIR) as a tool to enhance image quality with current standard full-dose imaging. MATERIALS AND METHODS: Twenty-five human cadavers were scanned (CT HD750) after contrast medium injection at different, decreasing dose levels D0-D5 and respectively reconstructed with MBIR. The data at full-dose level, D0, have been additionally reconstructed with standard adaptive statistical iterative reconstruction (ASIR), which represented the full-dose baseline reference (FDBR). Two radiologists independently compared image quality (IQ) in 3-mm multiplanar reformations for soft-tissue evaluation of D0-D5 to FDBR (-2, diagnostically inferior; -1, inferior; 0, equal; +1, superior; and +2, diagnostically superior). For statistical analysis, the intraclass correlation coefficient (ICC) and the Wilcoxon test were used. RESULTS: Mean CT dose index values (mGy) were as follows: D0/FDBR = 10.1 ± 1.7, D1 = 6.2 ± 2.8, D2 = 5.7 ± 2.7, D3 = 3.5 ± 1.9, D4 = 1.8 ± 1.0, and D5 = 0.9 ± 0.5. Mean IQ ratings were as follows: D0 = +1.8 ± 0.2, D1 = +1.5 ± 0.3, D2 = +1.1 ± 0.3, D3 = +0.7 ± 0.5, D4 = +0.1 ± 0.5, and D5 = -1.2 ± 0.5. All values demonstrated a significant difference to baseline (P < .05), except mean IQ for D4 (P = .61). ICC was 0.91. CONCLUSIONS: Compared to ASIR, MBIR allowed for a significant dose reduction of 82% without impairment of IQ. This resulted in a calculated mean effective dose below 1 mSv