T2 and T1rho have potential to nondestructively detect cartilage degeneration. However, reports in the literature regarding their diagnostic interpretation are conflicting. In this study, T2 and T1rho were measured at 8.5 T in several systems: 1) Molecular suspensions of collagen and GAG (pure concentration effects): T2 and T1rho demonstrated an exponential decrease with increasing [collagen] and [GAG], with [collagen] dominating. T2 varied from 90 to 35 ms and T1rho from 125 to 55 ms in the range of 15-20% [collagen], indicating that hydration may be a more important contributor to these parameters than previously appreciated. 2) Macromolecules in an unoriented matrix (young bovine cartilage): In collagen matrices (trypsinized cartilage) T2 and T1rho values were consistent with the expected [collagen], suggesting that the matrix per se does not dominate relaxation effects. Collagen/GAG matrices (native cartilage) had 13% lower T2 and 17% lower T1rho than collagen matrices, consistent with their higher macromolecular concentration. Complex matrix degradation (interleukin-1 treatment) showed lower T2 and unchanged T1rho relative to native tissue, consistent with competing effects of concentration and molecular-level changes. In addition, the heterogeneous GAG profile in these samples was not reflected in T2 or T1rho. 3) Macromolecules in an oriented matrix (mature human tissue): An oriented collagen matrix (GAG-depleted human cartilage) showed T2 and T(1rho) variation with depth consistent with 16-21% [collagen] and/or fibril orientation (magic angle effects) seen on polarized light microscopy, suggesting that both hydration and structure comprise important factors. In other human cartilage regions, T2 and T1rho abnormalities were observed unrelated to GAG or collagen orientation differences, demonstrating that hydration and/or molecular-level changes are important. Overall, these studies illustrate that T2 and T1rho are sensitive to biologically meaningful changes in cartilage. However, contrary to some previous reports, they are not specific to any one inherent tissue parameter.
Background and Purpose-Brain regions normal on diffusion-weighted imaging (DWI) but abnormal on mean transit time (MTT) maps represent tissue at risk of infarction, yet the fate of these regions is quite variable. The imperfect correlation between tissue outcome and initial imaging parameters suggests that each patient's brain may have different susceptibility to ischemic stress. We hypothesize that age is a marker for tissue susceptibility to ischemia and thus plays a role in determining tissue outcome in human stroke. Methods-Sixty patients with acute ischemic stroke and a region of DWI/MTT mismatch that was Ͼ20% of the DWI volume were included. All patients were scanned twice, within 12 hours of symptom onset and on day 5 or later. The percentage mismatch lost (PML) was calculated as percentage of initial DWI/MTT mismatch volume that was infarcted on the follow-up MRI. The statistical analysis explored relationships among the covariates age, Trial of Org 10172 in Acute Stroke Treatment (TOAST) subtypes, time-to-MRI, and initial DWI, MTT volume, mean arterial blood pressure and blood glucose level at admission, and previous history of hypertension and diabetes mellitus. Results-Univariate comparisons showed that age (Pϭ0.003), hypertension (Pϭ0.009), and diabetes mellitus (Pϭ0.0002)were significantly associated with PML. Regression analyses showed age to be a significant covariate (Pϭ0.02). The regression model predicted a change in PML of Ϸ0.65% per year. The adjusted proportion of variance (R 2 ) in PML that could be explained by age alone was 14%. Conclusion-Age-dependent increase in conversion of ischemic tissue into infarction suggests that age is a biological marker for the variability in tissue outcome in acute human stroke.
Background and Purpose-The severity of the neurological deficit after ischemic stroke is moderately correlated with infarct volume. In the current study, we sought to quantify the impact of location on neurological deficit severity and to delineate this impact from that of volume. Methods-We developed atlases consisting of location-weighted values indicating the relative importance in terms of neurological deficit severity for every voxel of the brain. These atlases were applied to 80 first-ever ischemic stroke patients to produce estimates of clinical deficit severity. Each patient had an MRI and National Institutes of Health Stroke Scale (NIHSS) examination just before or soon after hospital discharge. The correlation between the location-based deficit predictions and measured neurological deficit (NIHSS) scores were compared with the correlation obtained using volume alone to predict the neurological deficit. Results-Volume-based estimates of neurological deficit severity were only moderately correlated with measured NIHSS scores (rϭ0.62).
Diffusion is sensitive to early ischemia and follows a different time course than that of changes observed with gadolinium enhancement. ADC remained elevated in this model of severe, prolonged ischemia despite the spontaneous partial restoration of blood flow seen on gadolinium-enhanced images.
Purpose: To investigate the utility of an automated perfusion-weighted MRI (PWI) method for estimating cerebral blood flow (CBF) based on localized arterial input functions (AIFs) as compared to the standard method of manual global AIF selection, which is prone to deconvolution errors due to the effects of delay and dispersion of the contrast bolus. Materials and Methods:Analysis was performed on spinand gradient-echo EPI images from 36 stroke patients. A local AIF algorithm created an AIF for every voxel in the brain by searching out voxels with the lowest delay and dispersion, and then interpolating and spatially smoothing them for continuity. A generalized linear model (GLM) for predicting tissue outcome, and MTT lesion volumes were used to quantify the performance of the localized AIF method in comparison with global methods using ipsilateral and contralateral AIFs. Results:The algorithm found local AIFs in each case without error and generated a higher area under the receiver operating characteristic (ROC) curve compared to both global-AIF methods. Similarly, the local MTT lesion volumes had the least mean squared error (MSE). Conclusion:Automated CBF calculation using local AIFs is feasible and appears to produce more useful CBF maps.
Background Legg-Calvé-Perthes disease (LCP) is thought to be associated with ischemic events in the femoral head. However, the types and patterns of reperfusion after these ischemic events are unclear. Purposes We therefore determined whether (1) there would be any age-related diffusion changes; (2) diffusionweighted MR imaging would reveal ischemic damage; and (3) diffusion changes are correlated with prognostic MR findings in patients with LCP. Methods We prospectively performed conventional, perfusion, and diffusion-weighted MR imaging studies in 17 children with unilateral LCP. We then measured the apparent diffusion coefficient (ADC) values in the epiphysis and the metaphysis, and compared them with those of the contralateral normal side. Based on perfusion MR imaging, we assessed reperfusion to the epiphysis as either periphyseal or transphyseal. We studied T2-signal intensity changes in the metaphysis and the presence of focal physeal irregularity. We correlated diffusion changes with reperfusion to the epiphysis, T2-signal intensity change, and focal physeal irregularity. Results Normal diffusion decreased with age. In LCP hips, epiphyseal diffusion increased early and remained elevated through the healing stage. Six of the 17 patients who had a metaphyseal ADC greater than 50% over the Each author certifies that he or she has no commercial associations (eg, consultancies, stock ownership, equity interest, patent/licensing arrangements, etc) that might pose a conflict of interest in connection with the submitted article. Each author certifies that his or her institution approved the human protocol for this investigation, that all investigations were conducted in conformity with ethical principles of research, and that informed consent for participation in the study was obtained. 123Clin Orthop Relat Res (2011) 469:2881-2888 DOI 10.1007/s11999-011-1931 normal side had 13 times greater odds of having an association with transphyseal reperfusion to the epiphysis. The increase of metaphyseal ADC also was associated with an increased T2-signal intensity in the metaphysis and presence of focal physeal irregularity. Conclusions Diffusion-weighted MR imaging can be used as a complimentary modality to evaluate ischemic tissue damage with a potential prognostic value in patients with LCP.
T 2 information and delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) are both used to characterize articular cartilage. They are currently obtained in separate studies because Gd-DTPA 2؊ (which is needed for dGEMRIC) affects the inherent T 2 information. In this study, T 2 was simulated and then measured at 8.45 T in 20 sections from two human osteochondral samples equilibrated with and without Gd-DTPA 2؊. Both the simulations and data demonstrated that Gd-DTPA 2؊ provides a non-negligible mechanism for relaxation, especially with higher (1 mM) equilibrating Gd-DTPA 2؊ concentrations, and in areas of tissue with high T 2 (due to weak inherent T 2 mechanisms) and high tissue Gd-DTPA 2؊ (due to a low glycosaminoglycan concentration). Nonetheless, T 2 -weighted images of cartilage equilibrated in 1 mM Gd-DTPA 2؊ showed similar T 2 contrast with and without Gd-DTPA 2؊, demonstrating that the impact on T 2 was not great enough to affect identification of T 2 lesions. However, T 2 maps of the same samples showed loss of conspicuity of T 2 abnormalities. We back-calculated inherent T 2 's (T 2,bc ) using a T 2 -relaxivity value from a 20% protein phantom (r 2 ؍ 9.27 ؎ 0.09 mM ؊1 s ؊1) and the Gd-DTPA 2؊ concentration calculated from T 1,Gd . The back-calculation restored the inherent T 2 conspicuity, and a correlation between T 2 and T 2,bc of r ؍ 0.934 (P < 0.0001) was found for 80 regions of interest (ROIs) in the sections. Backcalculation of T 2 is therefore a viable technique for obtaining T 2 maps at high equilibrating Gd-DTPA 2؊ concentrations. With T 2 -weighted images and/or low equilibrating Gd-DTPA 2؊ concentrations, it may be feasible to obtain both T 2 and dGEMRIC information in the presence of Gd-DTPA 2؊ without such corrections. These conditions can be designed into ex vivo studies of cartilage. They appear to be applicable for clinical T 2 studies, since pilot clinical data at 1.5 T from three volunteers demonstrated that calculated T 2 maps are comparable before and after "double dose" Gd-DTPA 2؊ (as utilized in clinical dGEMRIC studies). Therefore, it may be possible to perform a comprehensive clinical examination of dGEMRIC, T 2 , and cartilage volume in one scanning session without T 2 data correction.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.