Magnetization Transfer Ratio and Morphometrics of the Spinal Cord Associates with Surgical Recovery in Patients with Degenerative Cervical Myelopathy.

OBJECTIVES: We assessed the prognostic value of the preoperative magnetization transfer ratio (MTR) and morphometrics of the spinal cord in patients with degenerative cervical myelopathy (DCM) in a longitudinal cohort study. METHODS: Thirteen subjects with DCM underwent 3T magnetization transfer imaging. The MTR was calculated for the spinal cord regions and specific white matter tracts. Morphometric measures were extracted. Clinical (modified Japanese Orthopaedics Association [mJOA] and Nurick scale scores) and health-related quality of life scores were assessed before and after cervical decompression surgery. The association between the magnetic resonance imaging (MRI) metrics and postoperative recovery was assessed (Spearman's correlation). Receiver operating characteristics were used to assess the accuracy of MRI metrics in identifying ≥50% recovery in function. RESULTS: Preoperative anterior cord MTRs were associated with recovery in mJOA scores (ρ = 0.608; P = 0.036; area under the curve [AUC], 0.66). Preoperative lateral cord MTR correlated with the neck disability index (ρ = 0.699; P = 0.011) and pain interference scale (ρ = 0.732; P = 0.007). Preoperative rubrospinal tract MTR was associated with mJOA score recovery (ρ = 0.573; P = 0.041; AUC, 0.86). Preoperative corticospinal tract and reticulospinal MTRs were related to recovery in pain interference scores (ρ = 0.591; P = 0.033; and ρ = 0.583; P = 0.035, respectively). Eccentricity of the cord was associated with Nurick scores (ρ = 0.606; P = 0.028) and mJOA scores (ρ = 0.651; P = 0.025; AUC, 0.92). CONCLUSIONS: Preoperative MTR and eccentricity measurements of the spinal cord have prognostic value in assessing the response to surgery and recovery in patients with DCM. Advanced MRI and atlas-based postprocessing techniques can inform interventions and advance the healthcare received by patients with DCM.

Planar IGRT dose reduction: A practical approach.

PURPOSE: To retrospectively estimate the cumulative absorbed dose (at the skin) from kilovoltage planar x-rays received by 90 patients treated on a Varian iX and to determine if that dose could be reduced without sacrificing image quality. METHODS AND MATERIALS: To estimate surface dose, measurements were obtained using the "in-air" method by varying the source-to-detector distance from 80 to 100 cm in steps of 5 cm. Energy was varied from 70 to 120 kVp. Using these data, a global equation was developed to estimate the cumulative skin dose by applying the imaging settings (kVp, mAs), patient-specific source-to-skin distance, and total number of images. To reduce the imaging dose, anterior and lateral images of RANDO phantoms were obtained using the same kVp; however, the mAs settings were systematically reduced. Contrast-to-noise ratios (CNRs) were calculated for both the standard phantom images and reduced mAs images. The mAs values were chosen to minimize skin dose while maintaining a similar CNR. Last, daily kV anterior and lateral images were obtained using these reduced mAs settings for 7 patients currently being treated with image guided radiation therapy. CNR was determined and compared with the values obtained on images taken 1 day before this change. RESULTS: Average cumulative kV imaging dose was as large as 162.2 cGy for pelvic cases with standard kVp, mAs. Other doses varied by site and technique. By lowering mAs, this dose could be reduced by 49% with only a 0.9% decrease in CNR. For the 7 patients currently being treated with image guided radiation therapy, CNR values were not statistically different (P = .79), whereas the skin dose was reduced by an average of approximately 50%. CONCLUSIONS: kV planar imaging dose reduction should be considered, given the large cumulative skin dose for certain disease sites. When mAs are reduced, planar dose reduction is clinically feasible without sacrificing image quality.

Muscle-fat MRI: 1.5 Tesla and 3.0 Tesla versus histology.

INTRODUCTION: We evaluated muscle/fat fraction (MFF) accuracy and reliability measured with an MR imaging technique at 1.5 Tesla (T) and 3.0T scanner strengths, using biopsy as reference. METHODS: MRI was performed on muscle samples from pig and rabbit species (n = 8) at 1.5T and 3.0T. A chemical shift based 2-point Dixon method was used, collecting in-phase and out-of-phase data for fat/water of muscle samples. Values were compared with MFFs calculated from histology. RESULTS: No significant difference was found between 1.5T and 3.0T (P values = 0.41-0.96), or between histology and imaging (P = 0.83) for any muscle tested. CONCLUSIONS: RESULTS suggest that a 2-point Dixon fat/water separation MRI technique may provide reliable quantification of MFFs at varying field strengths across different animal species, and consistency was established with biopsy. The results set a foundation for larger scale investigation of quantifying muscle fat in neuromuscular disorders.