Investigators who are interested in spinal cord injury or CEST.The cellular and molecular compositions of spinal cord tissues are affected by injury. Here we report detailed changes in Z-spectra of abnormal areas around lesion sites after spinal cord injury, both regionally and longitudinally. Spatial correlations of Z-spectra were used to identify and describe molecular disruptions in the spinal cord.MRI acquisitions were obtained from anesthetized squirrel monkeys (isoflurane 0.7-1.2%) at 9.4T. Four monkeys underwent surgery to introduce unilateral dorsal column section at C4-C5 spinal cord level, and they were scanned at different time points for up to 24 weeks after the injury.¹ CEST imaging was performed to obtain Z-spectra using a continuous wave (CW) (5.0 s, 1.0 μT) irradiation pulse followed by a 2-shot SE-EPI readout with TR of 7.5 s, TE of 17.6 ms, resolution at 0.5x0.5x1 mm³, RF offsets varied from -2000 Hz to 2000 Hz with an interval of 80 Hz. Reference scans were obtained with an RF offset of 100 kHz. A peak-fitting algorithm was used to decompose Z-spectra into 5 overlapping Lorentzian-shaped peaks from amide (I), amine (II), hydroxyl (III), free water (IV), and aliphatic proton pools (V) around 3.5, 2.2, 1.2, 0 and -3.3 ppm RF offsets, respectively (Fig. 1). Pearson correlation coefficient (PCC) was calculated between Z-spectrum at each pixel and the averaged Z-spectrum of normal gray matter (GM). Abnormal regions were identified as those pixels with Z-spectra showing poor correlation with the average Z-spectrum from normal GM. The abnormal regions were further separated into ROIs of distinct Z-spectra. Parametric maps were produced showing the distributions of each of the proton pools based on their peak amplitudes.Figure 1 shows an anatomic image and the correlation map of the Z-spectra in an injured spinal cord. Regional molecular changes were observed on the lesion side in the PCC map (Fig. 1). Compared to GM, amide, amine and hydroxyl CEST effects were strong while the semisolid magnetization transfer (MT) and nuclear Overhauser enhancement (NOE) effects were weak in regions identified as cystic. In addition, higher peak amplitudes and narrower widths were observed for the large component of free water in cysts. Abnormal tissues around the lesion site also showed different Z-spectra compared to those of cysts and normal tissues. Different spectra were observed for normal tissues (ROI 1), scar tissues (ROI 2), abnormal tissues lateral (ROI 3) or caudal (ROI 4) to the lesion sites, and cysts (ROIs 5-7). Longitudinally, all the subjects exhibited recovery from SCI with the shrinking of the cysts (Fig. 2a), reduction of CEST effects, and increments of semisolid MT and NOE effects at/around the lesion site (Fig. 2b). The histological sections confirmed the formation of cysts in the injured spinal cord.¹Characteristic multi-pool features extracted from Z-spectra may enable the non-invasive assessment of progression and spontaneous recovery of spinal cord from traumatic injury.