Journal of Magnetic Resonance Imaging

BackgroundOptimizing a restriction spectrum imaging (RSI) model for the prostate could lead to improved characterization of diffusion in the prostate and better discrimination of tumors. PurposeTo determine optimal apparent diffusion coefficients (ADCs) for prostate RSI models and evaluate the number of tissue compartments required to best describe diffusion in prostate tissue. Study TypeRetrospective. Population/SubjectsForty-six patients who underwent an extended MRI examination for suspected prostate cancer; 23 had prostate tumors and 23 had no detectable cancer. Field strength/Sequence3T multi-shell diffusion weighted sequence. AssessmentRSI models with 2-5 tissue compartments were fit to multi-shell DWI data from the prostate to determine optimal compartmental ADCs. Signal contributions from the different tissue compartments were computed using these ADCs and compared between normal tissues (peripheral zone, transition zone, seminal vesicles) and tumors. Statistical TestsThe Bayesian Information Criterion (BIC) was used to evaluate the optimality of different RSI models. Model-fitting residual (as percent variance) was recorded to assess the models goodness-of-fit and whether it varied between anatomical regions of the prostate. Two-sample t-tests (=0.05) were used to determine the statistical significance of any differences observed in compartmental signal-fraction between normal prostate tissue and tumors. ResultsThe lowest BIC was observed from the 4-compartment model. Optimal ADCs for the 4 compartments were 5.2e-4, 1.9e-3, 3.0e-3, and >>3.0e-3 mm2/s. Tumor tissue showed the largest reduction in fitting residual by increasing model order. Prostate tumors had a significantly (P<<0.05) greater proportion of signal from compartments 1 and 2 than normal tissue. Tumor conspicuity in compartment 1 increased substantially with model order. Data ConclusionAmong the examined RSI models, the 4-compartment model best described the diffusion-signal characteristics of the prostate. Compartmental signal fractions revealed by such a model may improve discrimination between cancerous and benign prostate tissue.

ObjectivesTo evaluate proton density fat fraction (PDFF) and T2* measurements of the liver with combined parallel imaging (sensitivity encoding, SENSE) and compressed sensing (CS) accelerated chemical shift encoding-based water-fat separation. MethodsSix-echo Dixon imaging was performed in the liver of 89 subjects. The first acquisition variant used acceleration based on SENSE with a total acceleration factor equal to 2.64 (acquisition labeled as SENSE). The second acquisition variant used acceleration based on a combination of CS with SENSE with a total acceleration factor equal to 4 (acquisition labeled as CS+SENSE). Acquisition times were compared between acquisitions and proton density fat fraction (PDFF) and T2*-values were measured and compared separately for each liver segment. ResultsTotal scan duration was 14.5 sec for the SENSE accelerated image acquisition and 9.3 sec for the CS+SENSE accelerated image acquisition. PDFF and T2* values did not differ significantly between the two acquisitions (paired Mann-Whitney and paired t-test P>0.05 in all cases). CS+SENSE accelerated acquisition showed reduced motion artifacts (1.1%) compared to SENSE acquisition (12.3%). ConclusionCS+SENSE accelerates liver PDFF and T2*mapping while retaining the same quantitative values as an acquisition using only SENSE and reduces motion artifacts. Strengths of this studyO_LICompressed sensing allows accelerated imaging with reduction of motion artifacts without alteration of quantitative measurements C_LIO_LIRobust results in fat and iron quantification in a heterogeneous patient cohort C_LI Limitations of this studyO_LINo histopathological validation of the MR findings was performed C_LIO_LIThe study was not performed at different field strengths C_LI

BackgroundConventional distortion correction techniques include the Reversed Polarity Gradient (RPG) method and FSL-topup, which estimate tissue displacement from EPI images of opposite phase-encoding polarity, and scale image intensity by the Jacobian of the estimated displacement. PurposeTo demonstrate that Jacobian intensity correction (JIC) can cause misleading improvement of EPI image distortion. We propose an alternative distortion correction approach (multi-b RPG; mRPG) that eliminates the JIC factor by normalizing opposite-polarity EPI images across multiple b-values. Study typeRetrospective. Population163 prostate cancer patients without metallic implants. Fieldstrength/Sequence3T diffusion-weighted sequence with EPI readout, using multiple b-values. AssessmentMaps of spatial shift (distortion) were estimated from opposite-polarity EPI volumes using RPG, topup, and mRPG. The estimated spatial shifts from each method were then applied to correct the b=0s/mm2 images (both with and without JIC) and ADC maps (for which JIC is meaningless). Distortion was quantified by the Pearson correlation between opposite-polarity volumes. The distribution of correlation coefficients across all patients was examined for b=0s/mm2 images and ADC maps, before and after distortion correction by each method. The mean, median, and 10th percentile were reported for each distribution. Statistical testsWilcoxon signed-rank tests (=0.05) were used to assess whether correlation increased significantly after distortion correction by each method, and whether mRPG yielded a larger increase versus RPG or topup. ResultsMedian improvement in the correlation between b=0s/mm2 volumes was significantly smaller without JIC (p<0.001): 0.04 vs 0.16 (RPG), 0.06 vs 0.18 (topup). mRPG yielded significantly larger improvements compared to RPG or topup (p<0.001). b=0s/mm2: 0.09 vs 0.04 (RPG) and 0.06 (topup). ADC: 0.09 vs 0.02 (RPG) and 0.03 (topup). Data conclusionDisparity in the distortion-correction performance of conventional methods with and without JIC suggests underestimation of tissue displacement. mRPG shows improved correction of distortion artifacts compared to conventional methods.

BackgroundThe Restriction Spectrum Imaging restriction score (RSIrs) has demonstrated higher diagnostic accuracy for clinically significant prostate cancer (csPCa) than conventional DWI. Both diffusion and T2 properties of prostate tissue inform the RSI signal, and studies have shown that each may be valuable for csPCa discrimination. PurposeTo determine whether prostate T2 varies across RSI compartments and in the presence of csPCa, and to evaluate whether consideration of compartmental T2 (cT2) improves csPCa detection over RSIrs alone. Study TypeRetrospective. PopulationTwo cohorts (46 and 195 patients) scanned for csPCa. Field Strength/Sequence3T multi-b-value DWI acquired at multiple TEs. AssessmentcT2 values were computed from multi-TE RSI data and compared between RSI model compartments. csPCa detection was compared between RSIrs and a logistic regression model (LRM) for predicting the probability of csPCa using cT2 in combination with RSI measurements. Statistical TestsTwo-sample t-tests (=0.05) were used to compare cT2 values between compartments and between patients with and without csPCa. Area under the receiver operating characteristic curve (AUC) was used to evaluate csPCa detection performance. ResultsIn both cohorts, T2 differed (p<0.05) across all RSI compartments (C1, C2, C3, C4). Voxel-level data from cohort 1 showed that T2 differed between normal and cancerous tissue in C1, C2, C3 (p<0.001). Whole-prostate T2 differed between patients with and without csPCa in C3 (p=0.02). In cohort 2, whole-prostate T2 differed in C1 (p=0.01), C3 (p=0.01), and C4 (p<0.01). Consideration of cT2 improved csPCa discrimination compared to diffusion alone, but not compared to RSIrs [cohort 1: 0.80 vs 0.70 (diffusion) and 0.80 (RSIrs), cohort 2: 0.72 vs 0.65 (diffusion) and 0.72 (RSIrs)]. Data ConclusionSignificant differences in cT2 were observed between normal and cancerous prostatic tissue. With our data, however, consideration of cT2 did not significantly improve cancer detection performance over RSIrs alone.

BackgroundHigh b-value diffusion-weighted images (DWI) are used for detection of clinically significant prostate cancer (csPCa). To decrease scan time and improve signal-to-noise ratio, high b-value (>1000 s/mm2) images are often synthesized instead of acquired. PurposeQualitatively and quantitatively compare synthesized DWI (sDWI) to acquired (aDWI) for detection of csPCa. Study TypeRetrospective Subjects151 consecutive patients who underwent prostate MRI and biopsy. SequenceAxial DWI with b=0, 500, 1000, and 2000 s/mm2 using a 3T clinical scanner using a 32-channel phased-array body coil AssessmentWe synthesized DWI for b=2000 s/mm2 via extrapolation based on monoexponential decay, using b=0 and b=500 s/mm2 (sDWI500) and b=0, b=500, and b=1000 s/mm2 (sDWI1000). Differences between sDWI and aDWI were evaluated within regions of interest (ROIs). The maximum DWI value within each ROI was evaluated for prediction of csPCa. Classification accuracy was also compared to Restriction Spectrum Imaging restriction score (RSIrs), a previously validated biomarker based on multi-exponential DWI. Statistical TestsDiscrimination of csPCa was evaluated via area under the receiver operating characteristic curve (AUC). Statistical significance was assessed using bootstrap difference (two-sided =0.05). ResultsWithin the prostate, mean {+/-} standard deviation of percent mean differences between sDWI and aDWI signal were -46{+/-}35% for sDWI1000 and -67{+/-}24% for sDWI500. AUC for aDWI, sDWI500, sDWI1000, and RSIrs within the prostate 0.62[95% confidence interval: 0.53, 0.71], 0.63[0.54, 0.72], 0.65[0.56, 0.73] and 0.78[0.71, 0.86], respectively. When considering the whole field of view, classification accuracy and qualitative image quality decreased notably for sDWI compared to aDWI and RSIrs. Data ConclusionsDWI is qualitatively comparable to aDWI within the prostate. However, hyperintense artifacts are introduced with sDWI in the surrounding pelvic tissue that interfere with quantitative cancer detection and might mask metastases. In the prostate, RSIrs yields superior quantitative csPCa detection than sDWI or aDWI.

BackgroundDiffusion-weighted magnetic resonance imaging (DW-MRI) has demonstrated potential as an exogenous contrast-free diagnostic tool for breast cancer screening. Advanced non-Gaussian models of the DW-MRI signal provide insight into the tissue microstructure. Restriction spectrum imaging (RSI) is a mathematical framework that improves tumor conspicuity by decomposing the DW-MRI signal into separate diffusion components. The number of diffusion components and corresponding apparent diffusion coefficients (ADCs) optimal for RSI are organ-specific and determined empirically. The outputs of RSI are the signal contributions of each separable diffusion component. PurposeTo understand the diffusion-weighted MRI signal of cancerous and healthy breast tissues in the context of RSI. Study TypeProspective. Populations74 women, from two sites, with pathology-proven breast cancer. Field Strength/Sequence3.0T AssessmentThe DW-MRI signal was described using a linear combination of a variable number of exponential components. The ADC for each component was estimated across all voxels from control and cancer regions of interest (ROIs), patients and sites. Once ADCs were determined, the signal contributions of each diffusion component were estimated using these fixed ADC values. Conventional ADC (mono-exponential) values were also estimated. Statistical TestsThe relative fitting residual and relative Bayesian information criterion (BIC) were assessed. The signal contributions of each diffusion component were compared using analysis of variance (ANOVA) and post-hoc tests. ResultsEstimated ADCs for the bi-exponential model were D1,2 = 2.0 x 10-5 and D2,2 = 2.2 x 10-3 mm2/s, and D1,3=0, D2,3 = 1.4 x 10-3 and D3,3=10.2 x 10-3 mm2/s for tri-exponential model, which in practice is reduced to a bi-exponential model with an offset, or a three-component model. The relative fitting residuals of conventional ADC, bi-exponential and three-component models in control ROIs were 2.1%, 1.62%, and 1.03%, and 3.3%, 1.0%, and 0.3% for cancer ROIs. BIC was smaller for the three-component model, indicating an improved fitting of breast DW-MRI data compared to the bi-exponential model. ConclusionBreast DW-MRI signal was best described using a tri-exponential model. The signal contributions of the slower component in bi- or tri-exponential models were larger in tumor lesions. These data may be used as differential features between healthy and malignant breast tissues.

BackgroundAssessing the risk of drug-mediated liver injury (DILI) and liver-mediated drug-drug interactions (DDI) for new drugs requires biomarkers that respond to drug effects on hepatic transporters. Evidence in rats has shown that dynamic gadoxetate-enhanced MRI (DGE-MRI) is suitable for this purpose, but it is not known whether these findings translate to humans. PurposeTo determine the effects of rifampicin, a known inhibitor of hepatocyte transporters OATP1B and MRP2, on gadoxetate uptake and excretion rates in the liver of healthy volunteers. Materials and MethodsThis prospective study recruited 10 healthy volunteers, who were assessed on two separate visits. DGE-MRI was performed over two separate scans, one hour apart, due to the slow hepatic excretion of gadoxetate after inhibition. DGE was acquired with a fast (2.5 sec) 3D free-breathing protocol collecting data continuously for 50 minutes. Gadoxetate was injected at 1/8th of a clinical dose, escalated to 1/4th after the first 3 volunteers. On the second visit, rifampicin (600mg) was administered orally one hour before the start of the scan. Liver uptake and excretion rates were derived by modelling signal-time curves in aorta and liver. The effect of rifampicin was determined with a paired t-test with significance level at p<0.01. ResultsEight of the 10 participants (3 female/7 male, mean age 32) completed both visits. Rifampicin reduced hepatocellular uptake rate of gadoxetate by 93% (95%CI 91-95%, p<0.001). Biliary excretion rate was reduced by 50% (p=0.004) but the effect was more variable (95%CI 8- 92%). Both rates were reduced by rifampicin in every participant, except for the excretion rate of one participant who had low baseline levels. ConclusionMRI measurements of gadoxetate biliary excretion and liver uptake rates can robustly detect inhibition of hepatocellular function mediated via OATP1B and MRP2 transporters.

BackgroundT2-weighted MRI is standard for detecting clinically significant prostate cancer (csPCa) by identifying visible lesions that stand out from the background prostate. PurposeTo determine whether patients with csPCa have abnormal T2-weighted signal in non-lesion, background prostate tissue (BP). MethodsThis retrospective study included two patient cohorts who underwent 3T MRI examination for suspected csPCa. Median (urine-normalized) T2-weighted signal was computed for BP and compared between patients with and without csPCa. csPCa discrimination performance of T2-weighted BP signal was evaluated using area under receiver operating characteristic curves (AUC). T2 and S0 (a proxy for proton density) were computed and compared between patients with and without csPCa. T2 was also recomputed using larger buffers around csPCa lesions. csPCa discrimination performance was compared between two predictors: Restriction Spectrum Imaging (RSI) C1 and RSI C1 normalized by global prostate median T2-weighted signal. ResultsCohort 1: 46 patients (age: 64{+/-}10 years). Cohort 2: 151 patients (65{+/-}8 years). Urine-normalized T2-weighted signal was systematically lower in BP of subjects with csPCa (p[&le;]0.034) and indicated the presence of cancer (cohort 1: AUC=0.80; cohort 2: AUC=0.68). BP T2 was significantly lower in csPCa patients (p[&le;]0.011), while S0 was not (p[&ge;]0.30). BP T2 measurements were stable to within 5% with buffers from 0 to 30 mm around visible lesions. csPCa discrimination improved with incorporation of BP T2-weighted signal (cohort 1: AUC=0.72 for RSI C1 alone, versus 0.81 with BP T2-weighted signal; cohort 2: AUC=0.63 versus 0.76). ConclusionLower T2-weighted signal in BP suggests the presence of csPCa.

PurposeIt has been reported that diffusion weighted imaging (DWI) with ultrahigh b-value increases the diagnostic power of prostate cancer. DWI imaging with higher b-values is challenging as it commonly suffers from low signal to noise ratio (SNR), distortion and longer scan time. The aim of our study was to develop a technique for quantification of apparent diffusion coefficient (ADC) for higher b-values from lower b-value DW images. Materials and MethodsFifteen patient (7 malignant, 8 benign) with prostate cancer were included in this study retrospectively with the institutional ethical committee approval. All images were acquired at 3T MR scanner. The ADC values were calculated using mono-exponential model. Synthetic ADC (sADC) for higher b-value were computed using a log-linear model. Contrast ratio (CR) between prostate lesion and normal tissue on synthetic DWI (sDWI) was computed and compared with original DWI and ADC images. ResultsNo significant difference was observed between actual ADC and sADC for b-2000 in all prostate lesions. However; CR increased significantly (p=0.002, paired t-test) in sDWI as compared to DWI. Malignant lesions showed significantly lower sADC as compared to benign lesion (p=0.0116, independent t-test). Mean ({+/-}standard deviation) of sADC of malignant lesions was 0.601{+/-}0.06 and for benign lesions was 0.92 {+/-} 0.09 (10-3mm2/s). Discussion / ConclusionOur initial investigation suggests that the ADC values corresponding to higher b-value can be computed using log-linear relationship derived from lower b-values (b[&le;]1000). Our method might help clinician to decide the optimal b-value for prostate lesion identification.

Rationale and ObjectivesTo compare the a commercially available automatic and manually adjusted segmentation software program (DynaCAD (R)) to two ellipsoid volume methods using T2-weighted magnetic resonance imaging (MRI). Material and MethodsThis is a retrospective IRB-approved study of 146 patients randomly selected from 1600 consecutive men referred for T2-weighted MRI. All measurements were performed by a single expert senior radiologist. Total prostate volume was calculated using automatic DynaCAD (R) software (RCAD), manually adjusted DynaCAD (R) (ACAD), traditional ellipsoid method (TE) and a new alternative biproximate ellipsoid method (BE). Results were assessed with ANOVA and linear regression. ResultsMean volumes for RCAD, ACAD, BE and TE were 61.5, 58.4, 56, and 53.2 respectively. ANOVA showed no difference of the means (p> 0.05.) Linear regression showed a coefficient of determination (r 2) between ACAD and TE of 0.92 and between ACAD and BE of 0.90. Using the planigraphic-based segmented ACAD as the "gold standard, RCAD overestimated volume by 5%. TE and BE underestimated prostatic volume by 4% and 9% respectively. ACAD processing time was 4.5 to 9.5 minutes (mean=6.6 min.) compared to 1.5 to 3.0 minutes (mean=2.3 min.) for prolate ellipsoid methods. ConclusionManually adjusted MRI T2-weighted segmentation is likely the most accurate measure of total prostate volume. DynaCAD appears to fulfill that function, but manual adjustment of automatic misregistration of boundaries is necessary. ACAD and RCAD are best applied to research use. Ellipsoid methods are faster, more convenient, nearly as accurate and more practical for clinical use.

PurposeThe purpose of this study was to determine the quantitative variability of diffusion weighted imaging and apparent diffusion coefficient values across a large fleet of MR systems. Using a NIST traceable magnetic resonance imaging diffusion phantom, imaging was reproducible and the measurements were quantitatively compared to known values. MethodsA fleet of 23 clinical MRI scanners was investigated in this study. A NIST/QIBA DWI phantom was imaged with protocols provided with the phantom. The resulting images were analyzed and ADC maps were generated. User-directed region-of-interests on each of the different vials provided ADC measurements among a wide range of known ADC values. ResultsThree diffusion phantoms were used in this study and compared to one another. From the one-way analysis of the variance, the mean and standard deviation of the percent errors from each phantom were not significantly different from one another. The low ADC vials showed larger errors and variation and appear directly related to SNR. Across all the MR systems and data, the coefficient of variation was calculated and Bland-Altman analysis was performed. ADC measurements were similar to one another except for the vials with the lower ADC values, which had a higher coefficient of variation. ConclusionADC values among the three phantoms showed good agreement and were not significantly different from one another. The large percent errors seen primarily at the low ADC values were shown to be a consequence of the SNR dependence and very little bias was observed between magnetic strengths and manufacturers. ADC values between diffusion phantoms were not statistically significant. Future investigations will be performed to study differences in magnetic field strength, vendor, MR system models, gradients, and bore size. More data across different MR platforms would facilitate quantitative measurements for multi-platform and multi-site imaging studies. With the increasing usage of diffusion weighted imaging in the clinic, the characterization of ADC variability for MR systems provides an improved quality control over the MR systems.

PurposeTo report the precision of a technique of measuring the PZ thickness on T2-weighted MRI and report normal parameters in patients with normal-sized prostates. We also wanted to establish the mean and second standard deviations (2SD) above and below the mean as criteria for abnormally narrow or expanded PZ thickness. MethodsOf the initial 1566 consecutive cohort referred for evaluation for carcinoma based on elevated PSA (prostate specific antibody) or DRE (digital rectal examination), 132 separate subjects with normal-sized prostates were selected for this study. Mean age was 58.2 years (15-82). Median serum PSA was 6.2ng/ML (range, 0.3-145). Most were asymptomatic for lower urinary tract symptoms (LUTS). Inclusion criteria in this study required technically adequate T2-weighted MRI and total prostatic volume (TPV) [&le;] 25 cc. Exclusion criteria included post prostatic surgical and radiation patients, patients having had medical management or minimally invasive therapy for BPH, those being treated for prostatitis. Patients with suspected tumor expanding or obscuring measurement boundaries were also not considered. Transition zone (TZ) and peripheral zone (PZ) volumes were determined using the prolate ellipsoid model. Postero-lateral measurement of the PZ was obtained at the axial level of maximal transverse diameter of the prostate on a line drawn from the outer boundary of the TZ to the inner boundary of the external prostatic capsule. The data was normally distributed. Therefore, it was analyzed using the 2-sided student t-test and Pearson produce correlation statistic. ResultsMean pooled (composite) measurement for the postero-lateral PZ (PLPZ) was 10 mm (CI= 9.5-10.5 mm) with SD of 2.87 mm. Means were statistically the same for the 2 observers (p=0.75). Pearson correlation between the two observers was 0.63. ConclusionsIn a prostate [&le;] 25 cc volume the postero-lateral PZ should be no thicker than 15.8 mm and averages 10.0 mm. when measured in the maximal axial plane on MRI. These norms were independent of age or use of endorectal coil. The technique measurement demonstrated clinically useful precision.

PurposeDiffusion weighted (DW) echo-planar imaging (EPI) is prone to geometric and intensity distortions due to B0 inhomogeneities. Pulse sequences that excite spins within a reduced field-of-view (FOV) in the phase encoding (PE) direction have been developed to decrease such distortions. In addition, use of the reverse polarity gradient (RPG) method, a retrospective approach to correct distortion artifacts, has been shown to improve the localization of tumor lesions. The purpose of this work was to evaluate the performance of reduced-FOV acquisition and RPG in decreasing distortion artifacts for breast imaging. MethodsEPI data were acquired with full and reduced-FOV in a breast phantom and in a group of 170 women at 3T. The performance of RPG in correcting distortion artifacts in EPI data was evaluated using the mutual information (MI) metric between EPI and anatomical low-distortion images before and after distortion correction. ResultsRPG corrected distortions by 61% in full-FOV EPI and 48% in reduced-FOV EPI in a breast phantom. In patients, MI increased on average 13{+/-}8% and 8{+/-}6% for both full and reduced-FOV EPI data after distortion correction, respectively. The 95th percentile and maximum displacement between uncorrected and corrected full-FOV EPI datasets were 0.8{+/-}0.3cm and 1.9{+/-}0.3cm, and for reduced-FOV were 0.4{+/-}0.2cm and 1.3{+/-}0.3cm. ConclusionMinimal distortion was achieved with RPG applied to reduced-FOV EPI data. RPG improved distortions for full-FOV, but with more modest improvements and limited correction near the nipple.

Abstract SummaryO_ST_ABSIntroductionC_ST_ABSThe normal heart has remarkable metabolic flexibility that permits rapid switching between mitochondrial glucose oxidation and fatty acid (FA) oxidation to generate ATP. Loss of metabolic flexibility has been implicated in the genesis of contractile dysfunction seen in cardiomyopathy. Metabolic flexibility has been imaged in experimental models, using hyperpolarized (HP) [2-13C]pyruvate MRI, which enables interrogation of metabolites that reflect tricarboxylic acid (TCA) cycle flux in cardiac myocytes. This study aimed to develop methods, demonstrate feasibility for [2-13C]pyruvate MRI in the human heart for the first time, and assess cardiac metabolic flexibility. MethodsGood Manufacturing Practice [2-13C]pyruvic acid was polarized in a 5T polarizer for 2.5-3 hours. Following dissolution, QC parameters of HP pyruvate met all safety and sterility criteria for pharmacy release, prior to administration to study subjects. Three healthy subjects each received two HP injections and MR scans, first under fasting conditions, followed by oral glucose load. A 5cm axial slab-selective spectroscopy approach was prescribed over the left ventricle and acquired at 3s intervals on a 3T clinical MRI scanner. ResultsThe study protocol which included HP substrate injection, MR scanning and oral glucose load, was performed safely without adverse events. Key downstream metabolites of [2-13C]pyruvate metabolism in cardiac myocytes include the glycolytic derivative [2-13C]lactate, TCA-associated metabolite [5-13C]glutamate, and [1-13C]acetylcarnitine, catalyzed by carnitine acetyltransferase (CAT). After glucose load, 13C-labeling of lactate, glutamate, and acetylcarnitine from 13C-pyruvate increased by 39.3%, 29.5%, and 114%, respectively in the three subjects, that could result from increases in lactate dehydrogenase (LDH), pyruvate dehydrogenase (PDH), and CAT enzyme activity as well as TCA cycle flux (glucose oxidation). ConclusionsHP [2-13C]pyruvate imaging is safe and permits non-invasive assessment of TCA cycle intermediates and the acetyl buffer, acetylcarnitine, which is not possible using HP [1-13C]pyruvate. Cardiac metabolite measurement in the fasting/fed states provides information on cardiac metabolic flexibility and the acetylcarnitine pool. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=84 SRC="FIGDIR/small/23297053v1_ufig1.gif" ALT="Figure 1"> View larger version (36K): org.highwire.dtl.DTLVardef@10ef2faorg.highwire.dtl.DTLVardef@7205e3org.highwire.dtl.DTLVardef@1e07e69org.highwire.dtl.DTLVardef@18b5bf4_HPS_FORMAT_FIGEXP M_FIG C_FIG

BackgroundMyocardial T1 and T2 mapping provide a non-invasive quantitative assessment of cardiac tissue. While established at 1.5-T and 3.0-T MRI, the mapping performance and reference values at 5.0-T MRI remain to be investigated. This study aims to evaluate the feasibility and establish reference values for cardiac T1 and T2 mapping at 5.0-T MRI in healthy subjects. MethodsIn this prospective study, 50 healthy volunteers underwent cardiac MRI at both 3.0-T and 5.0-T MRI systems from February to April 2025. Mapping protocols included MOdified Look Locker Inversion recovery (MOLLI, T1), T2-prepared gradient-echo (T2-prep-GRE, T2), and a simultaneous multi-parametric mapping technique (Multimap, T1 and T2). At 3.0-T MRI, both balanced steady-state free precession (bSSFP) and fast low-angle shot (FLASH) readouts were employed, while only the FLASH readout was used at 5.0-T MRI. Intra-observer, inter-observer, and scan-rescan reproducibility were assessed. Statistical analyses included coefficient of variation (CoV), intraclass correlation coefficient (ICC), and Bland-Altman analysis. ResultsAll techniques at 5.0-T MRI yielded high-quality, artifact-free images. Native T1 values were significantly higher at 5.0 T than at 3.0-T MRI (MOLLI: 1452.9 {+/-} 33.2 ms vs. 1305.9 {+/-} 38.3 ms, P < 0.0001), while T2 values were significantly lower (T2-prep-GRE: 37.53 {+/-} 1.74 ms vs. 43.97 {+/-} 2.95 ms, P < 0.0001). Scan-rescan reproducibility at 5.0 T (ICC: 0.87-0.92; CoV: 2.41%-3.25%) was comparable to 3.0-T MRI. The measurement precision of 5.0 T was higher than 3.0-T MRI with FLASH readout and slightly inferior to bSSFP-based techniques. Multimap achieved efficient, simultaneous T1 and T2 quantification with acceptable reproducibility at 5.0-T MRI. ConclusionMyocardial T1 and T2 mapping at 5.0-T MRI are reliable and reproducible in healthy individuals, offering reference values for normal myocardium at this field strength. The good measurement reproducibility and precision of 5.0-T cardiac mapping support its clinical potential for myocardial tissue characterization.

Background & AimsFor a range of liver malignancies, the only curative treatment option may be hepatectomy, which may have fatal complications. Therefore, an unbiased pre-operative risk assessment is vital, however, at present the assessment is typically based on global liver function only. Magnetic resonance imaging (MRI) modalities have the possibility to aid this assessment, by introducing additional characterization of liver parenchymal, such as non-invasive quantification of steatosis, fibrosis, and uptake function, both for global and regional assessment. To this cause, we here present a prospective observation study (LIFE), in which patients underwent extensive MR-examinations both before and after resective-surgery. Approach and ResultsA total of 13 patients undergoing hepatectomy underwent a pre- (n=13) and post (m=5) multimodal MRI examination (within 3-5 days of the surgery) (Fig. 1B). The multimodal MR-examination included DCE, 3D-MRE, fat fraction measurements (PDFF by MRS, 6PD). Using these measurements, we also construct individual patient profiles by including conventional functional, and volumetric measurements, into a multi-parametric space. As a proof of concept, the areas of each profile, denoted multiparametric profile area (MPA, and aMPA) were calculated, to create a measurement comprising information from all modalities. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=165 SRC="FIGDIR/small/24302306v1_fig1.gif" ALT="Figure 1"> View larger version (35K): org.highwire.dtl.DTLVardef@1ce4181org.highwire.dtl.DTLVardef@2eb05eorg.highwire.dtl.DTLVardef@13d1057org.highwire.dtl.DTLVardef@1fbf9d5_HPS_FORMAT_FIGEXP M_FIG O_FLOATNOFigure 1:C_FLOATNO Study-design and the multi-modal magnetic resonance imaging (MRI) examination. (A) Multi-modal MR-protocol and conventional function test. The examination can be divided into five segments. The first segment (dark green box) was the elastography (MRE) at 33 Hz vibration frequency, measuring tissue stiffness. The second segment (teal) was dynamic contrast enhanced (DCE) MRI using the hepatocyte specific contrast agent gadoxetic acid (Gd-EOB-DTPA, Primovist, Bayer Schering Pharma, Berlin, Germany). The third box (light green) was quantitative MRI. Fat fraction via both spectroscopy (MRS) and 6-Point Dixon imaging (6PD). Also, the liver iron content (LIC) was estimated using the relaxation rate R2* obtained via standard T2-weighted imaging. We also performed laboratory function tests including galactose breath test (GBT), Indocyanine Green retention rate (R15) and disappearance rate (PDR), as well as measured bilirubin and albumin. (B) Study setup. A total of 13 patients, all undergoing hepatectomy, underwent a multi-modal MRI examination 3-5 days before and after surgery. A total of five patients were able and willing to undergo the post-surgery MRI examination. C_FIG At a group-level, no clear pattern emerged of MPA or aMPA between groups with different extent of resection. In contrast, on a case-by-case basis, several parameters contributed to high individual MPA or aMPA-values, suggesting tissue abnormalities. With respect to regional DCE measurements, i.e., relative enhancement at 20 minutes, a clear variation between function in segments, within and between the individuals, was observed. ConclusionsIn this combined pre- and post-observational case-based study ranging from very extensive (i) liver surgery to minor (ii), or none (iii), we aimed to describe how a multi-modal MRI examination before hepatectomy could yield valuable information for the pre-operative assessment, with a particular focus on a Couinaud-segmental level. The use of a multi-modal approach allows for a broad spectral characterization of several aspects of the remnant tissue. However, the effectiveness and clinical benefit of each parameter, and how to further optimize an abbreviated clinical MR-protocol needs to be confirmed.

PurposeBreast density (BD) is a significant risk factor for breast cancer, yet current assessment methods lack automation, quantification, and cross-platform consistency. This study aims to evaluate MagDensity, a novel magnetic resonance imaging (MRI)-based quantitative BD measure, for its validity and reliability across different imaging platforms. MethodsTen healthy volunteers participated in this prospective study, undergoing fat-water MRI scans on three scanners: 3T Siemens Prisma, 3T Siemens Biograph mMR, and 1.5T GE Signa. Great effort was made to schedule all scans within a narrow three-hour window on the same day to minimize any potential intraday variations, highlighting the logistical challenges involved. BD was assessed using the MagDensity technique, which included combining magnitude and phase images, applying a fat-water separation technique, employing an automated whole-breast segmentation algorithm, and quantifying the volumetric water fraction. The agreement between measures was analyzed using mean differences, two-tailed t-tests, Pearsons correlation coefficients, and Bland-Altman plots. ResultsNo statistically significant differences in BD measurements by MagDensity within the same field strength and vendor (3T Siemens), with high correlation (Pearsons r > 0.99) and negligible mean differences (< 0.2%). Cross-platform comparison between the 3T Siemens and the 1.5T GE scanners showed mean differences of < 5%. After linear calibration, these variations were reduced to insignificant levels, yielding a strong correlation (Pearsons r > 0.97) and mean differences within {+/-}0.2%. ConclusionMagDensity, an MRI-based BD measure, exhibits robustness and reliability across diverse scanner models, vendors, and field strengths, marking a promising advancement towards standardizing BD measurements across multiple MRI platforms. It provides a valuable tool for monitoring subtle longitudinal changes in BD, which is vital for breast cancer prevention and personalized treatment strategies.

IntroductionPotassium is essential in cellular functions, with specific importance in muscle activity and cardiovascular health. It is the main intracellular cation in the human body with 70% located in muscle. Traditional methods to measure potassium levels are invasive and lack specificity for intracellular concentrations. Recently, non-invasive in vivo investigation of K+ ion homeostasis has become feasible by using K Magnetic Resonance Imaging (MRI) and MR spectroscopy (MRS) at ultrahigh magnetic fields. However, studies demonstrating the sensitivity of K MRI or MRS to detect potassium alterations in disease or upon intervention are sparse. This study utilizes K MRS to non-invasively track real-time intramuscular potassium changes during exercise, providing an assessment of potassium dynamics and explores the potential for technical artifacts in the measurements. MethodsFive healthy subjects (three males, two females) were recruited to perform standardized dynamic knee extensions inside a 7T MR scanner. Potassium levels were measured using a K MRS protocol that included periods of rest, moderate, and heavy exercise followed by recovery. Additionally, possible measurement artifacts due to muscle movement or changes in coil position relative to the thigh were evaluated using K MRS and H MRI monitoring in separate sessions. ResultsThe study revealed a consistent decrease in potassium levels during both moderate and heavy exercise, with an average decrease of 5-6%. These changes were rapidly detectable and were reversed upon cessation of exercise, indicating effective in vivo monitoring capability. Possible experimental artifacts were investigated, and the results suggested not to be responsible for the detected potassium changes during exercise. The results of the non-localized K MRS measurements during exercise correlated well with expected physiological changes based on previous literature. DiscussionThe application of K MRS provides a valuable non-invasive tool for studying potassium dynamics in human skeletal muscle. This technique could enhance our understanding of muscle physiology and metabolic disorders. The ability to measure these changes in real time and non-invasively highlights the potential for clinical applications, including monitoring of diseases affecting muscle and cellular metabolism.

PurposeTo develop and evaluate a free-breathing 2D radial joint T-T2 mapping technique for the kidneys at 3T, and to assess the impact of navigator gating parameters on mapping precision and accuracy. MethodsThe PARMANav sequence (PArametric Radial MApping with Navigator gating) was implemented for renal imaging, using 25 single-shot radial gradient echo acquisitions with five repeated magnetization preparations and lung-liver navigator gating to avoid through-plane motion. Virtual compressed coil and compressed sensing with spatial and contrast regularization was used for image reconstruction, followed by a model-based registration. An acquisition-specific joint T-T2 dictionary was generated using extended phase graph simulations. T1 and T2 accuracies were quantified in a phantom study versus gold standard spin-echo-based sequences. The influence of the navigator acceptance window width (NAWW) and navigator rejection on T1 and T2 precision were established in 10 healthy volunteers and were compared to routine T1 and T2 mapping. Three patients were scanned to demonstrate clinical feasibility. ResultsIn the phantom, PARMANav T1 and T2 values showed high accuracy with the gold standard T1 and T2 values and were insensitive to rejected navigators (< 5% variation for T1 and T2). As expected from previous studies, in-vivo renal PARMANav T1 and T2 values were higher than routine values but showed lower variability, both per subject and between subjects: in the cortex PARMANav T1=1601{+/-}48ms/T2=90.8{+/-}5.0ms vs routine T1=1307{+/-}108ms/T2=73.3{+/-}8.0ms, while in the medulla PARMANav T1=2044{+/-}82ms/T2 =90.3{+/-}5.4ms and routine T1=1560{+/-}122ms/T2=67.6{+/-}5.8ms. No T1 or T2 trend was observed for the different NAWW. Feasibility was demonstrated in patients, where high-quality maps were obtained. ConclusionPARMANav allows for precise and accurate joint T1-T2 mapping of the kidneys without requiring breath holding. Through-plane motion artifacts were avoided with a navigator, which did not impact the accuracy or precision of the resulting maps.

PurposeTo establish and optimize abdominal deuterium MRSI in conjunction with orally administered 2H-labelled molecules. MethodsA flexible transmit-receive surface coil was used to image naturally abundant deuterium signal in phantoms and healthy volunteers and after orally administered 2H2O in a patient with a benign renal tumor (oncocytoma). ResultsWater and lipid peaks were fitted with high confidence from both unlocalized spectra and from voxels within the liver, kidney, and spleen on spectroscopic imaging. Artifacts were minimal despite the high 2H2O concentration in the stomach immediately after ingestion, which can be problematic with the use of a volume coil. ConclusionWe have shown the feasibility of abdominal deuterium MRSI at 3 T using a flexible surface coil. Water measurements were obtained in healthy volunteers and images were acquired in a patient with a renal tumor after drinking 2H2O. The limited depth penetration of the surface coil may have advantages in characterizing early uptake of orally administered agents in abdominal organs despite the high concentrations in the stomach which can pose challenges with other coil combinations.