In vivo MRI of fresh stored osteochondral allograft transplantation with delayed gadolinium-enhanced MRI of cartilage: protocol considerations and recommendations.

The protocol for delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) was adapted for the evaluation of transplanted osteochondral allograft cartilage. Eight patients with focal grade 4 cartilage defects of the femoral condyle were treated with single cylindrical osteochondral allografts. At 1 and 2 years, dGEMRIC image sequences were acquired and regions of interest (ROIs) were drawn in repair and native control cartilage. Mean T1 values of region of interest were used to calculate established dGEMRIC metrics. The correlation was measured between the ΔR1 and R1 -Post metrics for repair and native cartilage. T1 times were measured in deep and superficial zones of cartilage. A strong correlation was identified between full-thickness, deep, and superficial ΔR1 and R1 -Post values for native cartilage and repair cartilage for all years (range: 0.893-1.0). The mean T1 times and ΔR1 rate between deep and superficial regions of articular cartilage were statistically different for all regions of the distal femora analyzed at 1 year and 2 years after osteochondral allograft transplantation (P<0.05). The dGEMRIC pre-Gadolinium scan is unnecessary when evaluating transplanted osteochondral allograft cartilage. The observation of stratified T1 and ΔR1 values indicates a need to re-evaluate the methodology behind the placement of region of interest in dGEMRIC.

Signal polarity restoration in a 3D inversion recovery sequence used with delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC).

PURPOSE: To develop an image reconstruction algorithm that restores the signal polarity in a three-dimensional inversion-recovery (3D-IR) sequence used in delayed gadolinium-enhanced MRI of cartilage (dGEMRIC). This approach effectively doubles the dynamic range of data used for T1 curve fitting. MATERIALS AND METHODS: We applied this reconstruction algorithm to a 3D-IR TFE sequence used for T1 mapping, validated the technique in a phantom study, and performed T1-map calculations in postosteochondral allograft transplant (OAT) patients. In addition, we performed a signal simulation study to assess the algorithm's capability to reduce the number of inversion times used in the 3D-IR TFE sequence. RESULTS: In comparison to a standard T1-mapping algorithm that uses the magnitude of the MRI signal, the proposed algorithm improves the reliability of T1 relaxation fits to the inversion-recovery three-parameter function. The signal simulation study shows that the number of TI inversion times can be reduced to as few as four, without compromising the accuracy of T1 calculations. CONCLUSION: This algorithm can be applied to any 2D- or 3D-IR acquisition sequence used in conjunction with dGEMRIC. Application of the algorithm improves the reliability of T1 calculations and allows the number of TIs to be reduced, leading to shorter scan times in dGEMRIC.

Measurement of brain iron distribution in Hallevorden-Spatz syndrome.

PURPOSE: To investigate spatial distribution of iron accumulation in the globus pallidus (GP) in patients with Hallevorden-Spatz syndrome (HSS) using phase imaging. We compared sensitivity of a phase imaging technique to relaxation rate measurement methods (R1,R2,R2*) for iron quantification. MATERIALS AND METHODS: R1, R2, and R2* were measured in GP structure of the brain of eight pantothenate kinase-associated neurodegeneration (PKAN) patients and a healthy volunteer using a 3T magnetic resonance imaging (MRI) scanner. The phase of gradient-echo images was preprocessed to eliminate phase 2pi wrapping and filtered to remove phase background variations. Phase gap across GP structure was used as a metric for iron effects quantification. RESULTS: Among the relaxation rates the most sensitive to iron accumulation was the R2* rate. The R1 and R2 rates demonstrated only small variations in this group of subjects. Up to an order of magnitude phase gap changes were measured between one PKAN patient and an age-matched healthy volunteer. Assuming that phase gap differences scale linearly with iron concentration we estimate that up to 2 mg Fe/g ww accumulates in GP of these patients. CONCLUSION: Our results demonstrate significantly higher sensitivity of the phase measurements for quantitative assessment of iron concentration compared to the relaxation rate measurements. Phase measurements could potentially be used for monitoring a progression and a response to therapy in PKAN.

Temporal in vivo assessment of fresh osteochondral allograft transplants to the distal aspect of the femur by dGEMRIC (delayed gadolinium-enhanced MRI of cartilage) and zonal T2 mapping MRI.

BACKGROUND: Zonal T2 mapping and dGEMRIC (delayed gadolinium-enhanced magnetic resonance imaging of cartilage) are diagnostic quantitative techniques to evaluate the biochemical health of articular cartilage. We adapted these techniques to investigate the results of osteochondral allograft transplantation and correlated the findings with patient-reported outcomes. METHODS: Nine patients with contained ICRS (International Cartilage Repair Society) grade-4 defects of the articular portion of a femoral condyle were treated with fresh osteochondral allografts and were evaluated prospectively with dGEMRIC and T2 mapping before and after gadolinium administration. The KOOS (Knee Injury Osteoarthritis Outcome Score) and IKDC (International Knee Documentation Committee) subjective scores were obtained at baseline and at one and two years postoperatively. For quantitative T2 mapping, regions of interest were drawn in the deep and superficial layers of allograft and control cartilage. For dGEMRIC analyses, the relaxation rate, post-gadolinium change in relaxation rate, and ratio between changes in the allograft and control regions of interest were calculated from T1 values. RESULTS: The mean ratio between the post-gadolinium changes in the allograft and control cartilage was 1.13 at one year and 1.55 at two years, and the ratio increased in eight of nine patients from one to two years. There was no difference between the mean T2 values in the deep zone of the allograft and control cartilage at one or two years (p > 0.05), but mean T2 values were higher in the superficial zone of the allograft cartilage at one (p < 0.0001) and two (p < 0.028) years. The mean improvement from baseline was significant at one and two years for the IKDC and all five KOOS subdomains (p < 0.05). All or nearly all patients showed improvements in all clinical outcomes scores at one year. CONCLUSIONS: Functional MRI techniques can be applied to noninvasively assess the biochemical health of cartilage after osteochondral allograft transplantation. The MRI findings correlated with certain patient-reported outcomes in the early postoperative period. Relative glycosaminoglycan content and the collagen structure of allograft cartilage may undergo time-dependent degeneration. A patient's perception of clinical outcome and quality of life is likely multifactorial and is impacted by more than the health of the allograft cartilage.

Peripheral vascular disease: blinded study of dedicated calf MR angiography versus standard bolus-chase MR angiography and film hard-copy angiography.

PURPOSE: To compare the accuracy of contrast material-enhanced three-dimensional (3D) dedicated calf magnetic resonance (MR) angiography with that of bolus-chase MR angiography, with conventional angiography as the reference standard, in patients with symptomatic peripheral vascular disease (PVD). MATERIALS AND METHODS: Thirty men with symptomatic PVD were examined. MR angiography was performed at 1.5 T before conventional angiography. MR angiographic examination included 3D contrast-enhanced dedicated calf MR angiography and three-station bolus-chase MR angiography. Two radiologists blinded to conventional angiographic results evaluated the MR angiograms independently. Two angiographers evaluated the conventional angiograms in consensus. Calf artery segments were graded as having 50% or less stenosis, greater than 50% stenosis, or occlusion or as being nondiagnostic. Statistical analyses were performed with paired permutation testing. RESULTS: Analyses of 472 calf segments and 420 pelvic and thigh segments were performed. Of the 472 calf segments, three and 75 segments (reader 1) and seven and 91 segments (reader 2) were graded as nondiagnostic at dedicated calf MR angiography and bolus-chase MR angiography, respectively. Differences in diagnostic grade between the two examinations were significant (P <.001), accounting for within-subject correlations, with a mean estimated difference of -17.1% (95% confidence interval [CI]: -25.8%, -8.4%). In the calf arteries, the dedicated and bolus-chase MR angiographic sequences had diagnostic accuracies, respectively, of 81.5% (reader 1) and 79.1% (reader 2) and of 67.8% (reader 1) and 63.4% (reader 2). The dedicated calf sequence was significantly more accurate than the bolus-chase sequence (P =.001). The point estimate of the difference was 14.7%, with estimated correct diagnosis rates of 80.3% and 65.6% for the dedicated calf and bolus-chase examinations, respectively (95% CI for difference: 4.0%, 25.4%). The diagnostic accuracy of bolus-chase MR angiography at the pelvis-thigh level was slightly higher when it was performed first: 81.9% (reader 1) and 83.8% (reader 2) versus 74.3% (reader 1) and 80.0% (reader 2) when it was performed last. The difference was not significant (P =.21). CONCLUSION: Use of dedicated calf MR angiography led to significantly increased diagnostic accuracy in the calf arteries compared with standard bolus-chase MR angiography. Use of the dual-bolus technique did not jeopardize the diagnostic accuracy in the pelvic and thigh arteries.