MRI

Diffusion weighted and dynamic contrast enhanced MRI as an imaging biomarker for stereotactic ablative body radiotherapy (SABR) of primary renal cell carcinoma

Abstract

Purpose
To explore the utility of diffusion and perfusion changes in primary renal cell carcinoma (RCC) after stereotactic ablative body radiotherapy (SABR) as an early biomarker of treatment response, using diffusion weighted (DWI) and dynamic contrast enhanced (DCE) MRI.

Methods
Patients enrolled in a prospective pilot clinical trial received SABR for primary RCC, and had DWI and DCE MRI scheduled at baseline, 14 days and 70 days after SABR. Tumours <5cm diameter received a single fraction of 26 Gy and larger tumours received three fractions of 14 Gy. Apparent diffusion coefficient (ADC) maps were computed from DWI data and parametric and pharmacokinetic maps were fitted to the DCE data. Tumour volumes were
contoured and statistics extracted. Spearman’s rank correlation coefficients were computed between MRI parameter changes versus the percentage tumour volume change from CT at 6, 12 and 24 months and the last follow-up relative to baseline CT.

Results
Twelve patients were eligible for DWI analysis, and a subset of ten patients for DCE MRI analysis. DCE MRI from the second follow-up MRI scan showed correlations between the change in percentage voxels with washout contrast enhancement behaviour and the change in tumour volume (ρ = 0.84, p = 0.004 at 12 month CT, ρ = 0.81, p = 0.02 at 24 month CT, and ρ = 0.89, p = 0.001 at last follow-up CT). The change in mean initial rate of
enhancement and mean Ktrans at the second follow-up MRI scan were positively correlated with percent tumour volume change at the 12 month CT onwards (ρ = 0.65, p = 0.05 and ρ = 0.66, p = 0.04 at 12 month CT respectively). Changes in ADC kurtosis from histogram analysis at the first follow-up MRI scan also showed positive correlations with the percentage tumour volume change (ρ = 0.66, p = 0.02 at 12 month CT, ρ = 0.69, p = 0.02
at last follow-up CT), but these results are possibly confounded by inflammation.

Conclusion
DWI and DCE MRI parameters show potential as early response biomarkers after SABR for primary RCC. Further prospective validation using larger patient cohorts is warranted.

Role of tissue perfusion, muscle strength recovery and pain in rehabilitation after acute muscle strain injury: A randomized controlled trial comparing early and delayed rehabilitation

Muscle strain injuries disrupt the muscle‐tendon unit, early rehabilitation is associated with a faster return to sports (RTS), but the time course of tissue healing remains sparsely described. The purpose was to examine tissue regeneration and the effectiveness of early versus delayed rehabilitation onset on functional and structural recovery after strain injuries. 50 recreational athletes with a severe acute strain injury in their thigh or calf muscles were randomized to early or delayed rehabilitation onset. Magnetic resonance imaging (MRI) was obtained initially, 3 and 6 months post injury and dynamic contrast‐enhanced MRI (DCE‐MRI) estimated tissue inflammation initially and after 6 months. Muscle strength was determined 5 weeks, 3 and 6 months post injury and a questionnaire determined soreness, pain and confidence. DCE‐MRI microvascular perfusion was higher in the injured compared to an uninjured muscle acutely (p< 0.01) and after 6 months (p< 0.01), for both groups (p> 0.05) and unrelated to RTS (p> 0.05). Total volume of the injured muscle decreased from the acute to the 3 months scan, and to the 6 months scan (p< 0.01) in both groups. Muscle strength was similar in both groups at any time. There was a non‐significant trend (p≤ 0.1) towards less pain and higher confidence with early rehabilitation. One re‐injury was recorded. In conclusion, our data showed prolonged tissue repair with the initial response linked to muscle atrophy but did not explain why early rehabilitation onset accelerated recovery considering that structural and functional recovery was similar with early and delayed rehabilitation.