Skeletal Health and Bone Marrow Composition in Newly Diagnosed Adolescents With Crohn Disease

Coronal T1 weighted spin echo images will be obtained through the knee with a field of view of 16cm to include distal femoral and proximal tibial metaphyses.

Spin-lattice relaxation (T1) relaxometry acquisition consisting of seven fast spin echo (FSE) acquisitions through the knee. T1 maps from the T1 relaxometry images will be generated using a two-parameter-fit iterative algorithm developed in-house using IDL software (Harris Geospatial Solutions, Melbourne, FL, USA). Mean T1 values for each region will be recorded. The anatomical locations of these regions will be consistent in size for all subjects and location. The locations chosen for the primary endpoints are ones that are known to be rich in red and yellow marrow, respectively.

Magnetic resonance spectroscopy. MRS will be performed within a 1 mL voxel situated in the medial aspect of the distal femoral metaphysis. A single voxel point resolved spectral acquisition (PRESS) technique will be used to acquire non-water suppressed spectra at echo times of 20, 30, 40, and 50 ms using 32 signal averages per echo time with a TR of 2.5 s (total scan time = 5.4 minutes). Spectral fits using JMRUI MRS processing software (www.jmrui.eu) to the water and methylene/methyl resonances will be used to quantify peak areas and establish T2 corrected fat/(fat + water) ratios.

Blood draw. Blood draws will be used to attain and assess markers of bone formation/resorption and to perform immune studies. Specific markers of bone formation that will be assessed include osteocalcin (OC) and procollagen type 1 N-terminal propeptide (P1NP), and a marker of bone resorption, c-telopeptide (CTX). We will also evaluate molecular gene signatures from the blood samples that correlate with the previously described bone imaging phenotypes. At that point, the information will be used to develop a CyTOF panel to evaluate differences in immune cellular populations between CD patients with normal versus low BMD, and matched controls.