Retrospective motion correction through multi-average k-space data elimination (REMAKE) for free-breathing cardiac cine imaging.

PURPOSE: To develop a motion-robust reconstruction technique for free-breathing cine imaging with multiple averages. METHOD: Retrospective motion correction through multiple average k-space data elimination (REMAKE) was developed using iterative removal of k-space segments (from individual k-space samples) that contribute most to motion corruption while combining any remaining segments across multiple signal averages. A variant of REMAKE, termed REMAKE+, was developed to address any losses in SNR due to k-space information removal. With REMAKE+, multiple reconstructions using different initial conditions were performed, co-registered, and averaged. Both techniques were validated against clinical "standard" signal averaging reconstruction in a static phantom (with simulated motion) and 15 patients undergoing free-breathing cine imaging with multiple averages. Quantitative analysis of myocardial sharpness, blood/myocardial SNR, myocardial-blood contrast-to-noise ratio (CNR), as well as subjective assessment of image quality and rate of diagnostic quality images were performed. RESULTS: In phantom, motion artifacts using "standard" (RMS error [RMSE]: 2.2 ± 0.5) were substantially reduced using REMAKE/REMAKE+ (RMSE: 1.5 ± 0.4/1.0 ± 0.4, p < 0.01). In patients, REMAKE/REMAKE+ led to higher myocardial sharpness (0.79 ± 0.09/0.79 ± 0.1 vs. 0.74 ± 0.12 for "standard", p = 0.004/0.04), higher image quality (1.8 ± 0.2/1.9 ± 0.2 vs. 1.6 ± 0.4 for "standard", p = 0.02/0.008), and a higher rate of diagnostic quality images (99%/100% vs. 94% for "standard"). Blood/myocardial SNR for "standard" (94 ± 30/33 ± 10) was higher vs. REMAKE (80 ± 25/28 ± 8, p = 0.002/0.005) and tended to be lower vs. REMAKE+ (105 ± 33/36 ± 12, p = 0.02/0.06). Myocardial-blood CNR for "standard" (61 ± 22) was higher vs. REMAKE (53 ± 19, p = 0.003) and lower vs. REMAKE+ (69 ± 24, p = 0.007). CONCLUSIONS: Compared to "standard" signal averaging reconstruction, REMAKE and REMAKE+ provide improved myocardial sharpness, image quality, and rate of diagnostic quality images.

Quantification of balanced SSFP myocardial perfusion imaging at 1.5 T: Impact of the reference image.

PURPOSE: To investigate the use of a high flip-angle (HFA) balanced SSFP (bSSFP) reference image (in comparison to conventional proton density [PD]-weighted reference images) for conversion of bSSFP myocardial perfusion images into dynamic T1 maps for improved myocardial blood flow (MBF) quantification at 1.5 T. METHODS: The HFA-bSSFP (flip angle [FA] = 50°), PD gradient-echo (PD-GRE; FA = 5°), and PD-bSSFP (FA = 8°) reference images were acquired before a dual-sequence bSSFP perfusion acquisition. Simulations were used to study accuracy and precision of T1 and MBF quantification using the three techniques. The accuracy and precision of T1 , and the precision and intersegment variability of MBF were compared among the three techniques in 8 patients under rest conditions. RESULTS: In simulations, HFA-bSSFP demonstrated improved T1 /MBF precision (higher T1 /MBF SD of 30%-80%/50%-100% and 30%-90%/60%-115% for PD-GRE and PD-bSSFP, respectively). Proton density-GRE and PD-bSSFP were more sensitive to effective FA than HFA-bSSFP (maximum T1 /MBF errors of 13%/43%, 20%/43%, and 1%/3%, respectively). Sensitivity of all techniques (defined as T1 /MBF errors) to native T1 , native T2 , and effective saturation efficiency were negligible (<1%/<1%), moderate (<14%/<19%), and high (<63%/<94%), respectively. In vivo, no difference in T1 accuracy was observed among HFA-bSSFP, PD-GRE, and PD-bSSFP (-9 ± 44 ms vs -28 ± 55 ms vs -22 ± 71 ms, respectively; p > .08). The HFA-bSSFP led to improved T1 /MBF precision (T1 /MBF SD: 41 ± 19 ms/0.24 ± 0.08 mL/g/min vs PD-GRE: 48 ± 20 ms/0.29 ± 0.09 mL/g/min and PD-bSSFP: 59 ± 23 ms/0.33 ± 0.11 mL/g/min; p ≤ .02) and lower MBF intersegment variability (0.14 ± 0.09 mL/g/min vs PD-GRE: 0.21 ± 0.09 mL/g/min and PD-bSSFP: 0.20 ± 0.10 mL/g/min; p ≤ .046). CONCLUSION: We have demonstrated the feasibility of using a HFA-bSSFP reference image for MBF quantification of bSSFP perfusion imaging at 1.5 T. Results from simulations demonstrate that the HFA-bSSFP reference image results in improved precision and reduced sensitivity to effective FA compared with conventional techniques using a PD reference image. Preliminary in vivo data acquired at rest also demonstrate improved precision and intersegment variability using the HFA-bSSFP technique compared with PD techniques; however, a clinical study in patients with coronary artery disease under stress conditions is required to determine the clinical significance of this finding.

Simultaneous multislice steady-state free precession myocardial perfusion with full left ventricular coverage and high resolution at 1.5 T.

PURPOSE: To implement and evaluate a simultaneous multi-slice balanced SSFP (SMS-bSSFP) perfusion sequence and compressed sensing reconstruction for cardiac MR perfusion imaging with full left ventricular (LV) coverage (nine slices/heartbeat) and high spatial resolution (1.4 × 1.4 mm2 ) at 1.5T. METHODS: A preliminary study was performed to evaluate the performance of blipped controlled aliasing in parallel imaging (CAIPI) and RF-CAIPI with gradient-controlled local Larmor adjustment (GC-LOLA) in the presence of fat. A nine-slice SMS-bSSFP sequence using RF-CAIPI with GC-LOLA with high spatial resolution (1.4 × 1.4 mm2 ) and a conventional three-slice sequence with conventional spatial resolution (1.9 × 1.9 mm2 ) were then acquired in 10 patients under rest conditions. Qualitative assessment was performed to assess image quality and perceived signal-to-noise ratio (SNR) on a 4-point scale (0: poor image quality/low SNR; 3: excellent image quality/high SNR), and the number of myocardial segments with diagnostic image quality was recorded. Quantitative measurements of myocardial sharpness and upslope index were performed. RESULTS: Fat signal leakage was significantly higher for blipped CAIPI than for RF-CAIPI with GC-LOLA (7.9% vs. 1.2%, p = 0.010). All 10 SMS-bSSFP perfusion datasets resulted in 16/16 diagnostic myocardial segments. There were no significant differences between the SMS and conventional acquisitions in terms of image quality (2.6 ± 0.6 vs. 2.7 ± 0.2, p = 0.8) or perceived SNR (2.8 ± 0.3 vs. 2.7 ± 0.3, p = 0.3). Inter-reader variability was good for both image quality (ICC = 0.84) and perceived SNR (ICC = 0.70). Myocardial sharpness was improved using the SMS sequence compared to the conventional sequence (0.37 ± 0.08 vs 0.32 ± 0.05, p < 0.001). There was no significant difference between measurements of upslope index for the SMS and conventional sequences (0.11 ± 0.04 vs. 0.11 ± 0.03, p = 0.84). CONCLUSION: SMS-bSSFP with multiband factor 3 and compressed sensing reconstruction enables cardiac MR perfusion imaging with three-fold increased spatial coverage and improved myocardial sharpness compared to a conventional sequence, without compromising perceived SNR, image quality, upslope index or number of diagnostic segments.

Use of rapid cardiac magnetic resonance imaging to guide chelation therapy in patients with transfusion-dependent thalassaemia in India: UMIMI study.

AIMS: To explore the impact of incorporating a faster cardiac magnetic resonance (CMR) imaging protocol in a low-middle-income country (LMIC) and using the result to guide chelation in transfusion-dependent patients. METHODS AND RESULTS: A prospective UK-India collaborative cohort study was conducted in two cities in India. Two visits 13 months apart included clinical assessment and chelation therapy recommendations based on rapid CMR results. Participants were recruited by the local patient advocate charity, who organized the patient medical camps. The average scanning time was 11.3 ± 2.5 min at the baseline and 9.8 ± 2.4 min (P < 0.001) at follow-up. The baseline visit was attended by 103 patients (mean age 25 years) and 83% attended the second assessment. At baseline, 29% had a cardiac T2* < 20 ms, which represents significant iron loading, and 12% had left ventricular ejection fraction <60%, the accepted lower limit in this population. Only 3% were free of liver iron (T2* ≥ 17 ms). At 13 months, more patients were taking intensified dual chelation therapy (43% vs. 55%, P = 0.002). In those with cardiac siderosis (baseline T2* < 20 ms), there was an improvement in T2*-10.9 ± 5.9 to 13.5 ± 8.7 ms, P = 0.005-and fewer were classified as having clinically important cardiac iron loading (T2* < 20 ms, 24% vs. 16%, P < 0.001). This is the first illustration in an LMIC that incorporating CMR results into patient management plans can improve cardiac iron loading. CONCLUSION: For thalassaemia patients in an LMIC, a simplified CMR protocol linked to therapeutic recommendation via the patient camp model led to enhanced chelation therapy and a reduction in cardiac iron in 1 year.

Comparative study of forage toxic metals of conventional versus non-conventional pastures in relation to animal mineral nutrient allowance.

At present, the forage production is the foundation of beef cattle and sheep industries in graziery. This study was designed to assess the toxic metal composition of the conventional pastures and non-conventional pastures in consideration of mineral needs of ruminants. At all the surveyed sites, these mean soil metal concentrations were measured to be higher or lower than the referred threshold levels. Specifically, these concentrations of Co, Pb, and Cr were observed as much higher than the referred threshold levels of 0.01-0.06 mg/kg (Co), 0.05 mg/kg (Pb), and 0.02 mg/kg (Cr). On the contrary, the mean soil concentrations of Cd were observed to be relatively lower than the threshold levels of 0.50-10 mg/kg at all sites. The estimated mean concentrations of Co, Cd, Pb, and Cr in both conventional and non-conventional forage species were measured to be lower than the referred threshold levels. The supplementation of these metals for livestock grazing from pasture was unnecessary based on these findings. However, further research should be conducted for ecological safety and conservation of ruminant forages, so that both the conventional and non-conventional pastures are employed as livestock friendly consuming forages.