Skeletal Health and Bone Marrow Composition in Adolescents With Cystic Fibrosis

Spin-lattice relaxation (T1) relaxometry acquisition consisting of 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 multiple echo times. 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 inflammation. 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). Additionally, in participants with CF, we will assess inflammation, with a c-reactive protein (CRP), and dysglycemia, with a continuous glucose monitor.

DXA will be utilized to obtain BMD of the total body, lumbar spine, and hip using a Hologic Horizon densitometer (Hologic Inc, Bedford, MA). Body composition will be obtained from total body scans.

pQCT will be utilized to obtain volumetric BMD (mg/cm3) of the left tibia. Measurements using a Stratec XCT 3000 device (Orthometrix, White Plains, NY) will be obtained at multiple locations, in relation to distal growth plate.