Combination Of Iterative Reconstruction Research Articles

Feasibility of 4DCBCT-based proton dose calculation: An ex vivo porcine lung phantom study

Inter-fractional variations of breathing pattern and patient anatomy introduce dose uncertainties in proton therapy. One approach to monitor these variations is to utilize the cone-beam computed tomography (CT, CBCT) scans routinely taken for patient positioning, reconstruct them as 4DCBCTs, and generate ‘virtual CTs’ (vCTs), combining the accurate CT numbers of the diagnostic 4DCT and the geometry of the daily 4DCBCT by using deformable image registration (DIR). In this study different algorithms for 4DCBCT reconstruction and DIR were evaluated.For this purpose, CBCT scans of a moving ex vivo porcine lung phantom with 663 and 2350 projections respectively were acquired, accompanied by an additional 4DCT as reference. The CBCT projections were sorted in 10 phase bins with the Amsterdam-shroud method and reconstructed phase-by-phase using first a FDK reconstruction from the Reconstruction Toolkit (RTK) and again an iterative reconstruction algorithm implemented in the Gadgetron Toolkit. The resulting 4DCBCTs were corrected by DIR of the corresponding 4DCT phases, using both a morphons algorithm from REGGUI and a b-spline deformation from Plastimatch. The resulting 4DvCTs were compared to the 4DCT by visual inspection and by calculating water equivalent thickness (WET) maps from the phantom's surface to the distal edge of a target from various angles. The optimized procedure was successfully repeated with mismatched input phases and on a clinical patient dataset. Proton treatment plans were simulated on the 4DvCTs and the dose distributions compared to the reference based on the 4DCT via gamma pass rate analysis.A combination of iterative reconstruction and morphons DIR yielded the most accurate 4DvCTs, with median WET differences under 2mm and 3%/3mm gamma pass rates per phase between 89% and 99%.These results suggest that image correction of iteratively reconstructed 4DCBCTs with a morphons DIR of the planning CT may yield sufficiently accurate 4DvCTs for daily time resolved proton dose calculations.

AIR-MRF: Accelerated iterative reconstruction for magnetic resonance fingerprinting

Existing approaches for reconstruction of multiparametric maps with magnetic resonance fingerprinting (MRF) are currently limited by their estimation accuracy and reconstruction time. We aimed to address these issues with a novel combination of iterative reconstruction, fingerprint compression, additional regularization, and accelerated dictionary search methods. The pipeline described here, accelerated iterative reconstruction for magnetic resonance fingerprinting (AIR-MRF), was evaluated with simulations as well as phantom and in vivo scans. We found that the AIR-MRF pipeline provided reduced parameter estimation errors compared to non-iterative and other iterative methods, particularly at shorter sequence lengths. Accelerated dictionary search methods incorporated into the iterative pipeline reduced the reconstruction time at little cost of quality.

Low-concentration contrast material for dual-source computed tomography coronary angiography by a combination of iterative reconstruction and low-tube-voltage technique: feasibility study

To assess the impact of low concentration contrast media on the degree of vascular enhancement, image quality and radiation dose in coronary CT angiography (cCTA) studies when using a combination of iterative reconstruction and low tube voltage. 120 patients who underwent cCTA were randomly divided into two groups. The patients in group A received iopromide 370 were scanned using the conventional tube output, and images were reconstructed using filtered back projection (FBP). The patients in group B received iodixanol 270 were scanned using the low tube output, and images were reconstructed using iterative reconstruction technique (SAFIRE, Siemens Healthcare). CT attenuation was measured in the coronary arteries, great arteries, interventricular septum and left ventricular cavity. Noise, subjective image quality scores and effective radiation dose were compared between the two groups. There was no significant difference in the mean CT attenuation achieved, image noise and mean image quality score at each anatomic site between iomeprol 270 group and iopromide 370 group. The effective radiation dose were 0.44 ± 0.25 mSv and 0.94 ± 0.42 mSv for iomeprol 270 and iopromide 370 in low weight subgroups, and 1.17 ± 0.30 mSv and 2.37 ± 0.66 mSv in high weight subgroups, respectively, reflecting dose savings of 53.2% (P < 0.01) and 50.6% (P < 0.01), respectively. The results demonstrate that with a combination of iterative reconstruction and a low tube voltage , a low iodine concentration of 270 mgI/ml still improves the contrast enhancement without impairing image quality, as well as significantly lowers effective radiation dose.

Low concentration contrast medium for dual-source computed tomography coronary angiography by a combination of iterative reconstruction and low-tube-voltage technique: Feasibility study

ObjectivesTo assess the impact of low-concentration contrast medium on vascular enhancement, image quality and radiation dose of coronary CT angiography (cCTA) by using a combination of iterative reconstruction (IR) and low-tube-voltage technique. Materials and methodsOne hundred patients were prospectively randomized to two types of contrast medium and underwent prospective electrocardiogram-triggering cCTA (Definition Flash, Siemens Healthcare; collimation: 128mm×0.6mm; tube current: 300mAs). Fifty patients received Iopromide 370 were scanned using the conventional tube setting (100kVp or 120kVp if BMI≥25kg/m2) and reconstructed with filtered back projection (FBP). Fifty patients received Iodixanol 270 were scanned using the low-tube-voltage (80kVp or 100kVp if BMI≥25kg/m2) technique and reconstructed with IR. CT attenuation was measured in coronary artery and other anatomical regions. Noise, image quality and radiation dose were compared. ResultsCompared with two Iopromide 370 subgroups, Iomeprol 270 subgroups showed no significant difference in CT attenuation (576.63±95.50 vs. 569.51±118.93 for BMI<25kg/m2, p=0.647 and 394.19±68.09 vs. 383.72±63.11 for BMI≥25kg/m2, p=0.212), noise (in various anatomical regions of interest) and image quality (3.5 vs. 4.0, p=0.13), but significantly (0.41±0.17 vs. 0.94±0.45 for BMI<25kg/m2, p<0.001 and 1.14±0.24 vs. 2.37±0.69 for BMI≥25kg/m2, p<0.001) lower radiation dose, which reflects dose saving of 56.4% and 51.9%, respectively. ConclusionsCombined IR with low-tube-voltage technique, a low-concentration contrast medium of 270mgI/ml can still maintain the contrast enhancement without impairing image quality, as well as significantly lower the radiation dose.

Rapid PROPELLER‐MRI: A combination of iterative reconstruction and under‐sampling

To develop a technique that is able to reduce acquisition time and remove uneven blurring in reconstructed image for PROPELLER MRI. By using under-sampling and iterative reconstruction, this proposed technique will be less sensitive to subject motion. Numerical simulations, as well as experiments on a phantom and healthy human subjects were performed to demonstrate advantages of a combination of under-sampled acquisition and iterative reconstruction. Method of motion correction was modified to increase accuracy of motion correction for the under-sampled PROPELLER acquisition. It was demonstrated that the proposed approach achieved substantial acceleration of PROPELLER acquisition while maintaining its motion correction advantage. An effective method for reducing imaging time in PROPELLER was introduced in this study, which minimizes typical under-sampling artifacts without uneven spatial resolution and maintains the ability of motion correction.