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Purpose: To investigate whether compressed air during air-cuff inflation in vascular reactivity studies could induce aberrant blood oxygenation level-dependent (BOLD) signal change., Materials and Methods: Magnetic resonance imaging (MRI) experiments were performed on a whole-body 3 T scanner. The pattern of T2* signal change measured from a phantom simulating the lower limb was assessed while a thigh cuff was inflated and deflated. MR spectroscopy was performed on a head phantom wrapped using a hand-cuff to determine the relationship between water peak linewidth and applied cuff pressure. Calf muscles from 14 normal subjects were examined to identify aberrant T2* signal changes in the occluded and nonoccluded legs., Results: A sudden T2* signal drop was observed in the phantom on initiation of cuff inflation with subsequent signal change being dependent on cuff pressure. Water peak linewidth increased linearly with cuff pressure (r(2) = 0.94). Aberrant T2* signal changes were observed in both the occluded and nonoccluded legs., Conclusion: Compressed air due to cuff inflation directly affects local magnetic field susceptibility. The T2* sequence is sensitive to local field disturbances induced by an inflated cuff. Muscle BOLD results are affected by high-pressure air, with a sudden drop in T2* signal being a characteristic feature of this induced effect., (Copyright © 2012 Wiley Periodicals, Inc.)

Purpose: To investigate vertebral bone marrow fat content in elderly subjects related to sex, age, and bone mineral density (BMD) and relate these findings to published data in younger subjects., Materials and Methods: A total of 259 healthy subjects (145 females, 114 males; age range, 62-90 years) underwent proton ((1) H) MR spectroscopy of L3 vertebral body and BMD of the lumbar spine with results stratified according to age. Ninety age- and BMD-matched subjects were selected to determine sex differences in marrow fat content and BMD., Results: In females, vertebral marrow fat content rose sharply between 55 and 65 years of age while in males vertebral marrow fat content rose gradually throughout life. Vertebral marrow fat content in females more than 60 years was approximately 10% higher in females than males, i.e., a reversal of sex difference reported in marrow fat content for subjects less than 60 years., Conclusion: Marrow fat content increases sharply in female subjects between 55 and 65 years of age while male subjects continue to increase marrow fat at a more gradual steady rate. Females older than 60 years have a higher marrow fat content than males. This increased deposition in marrow fat concurs with recognized changes in extraosseous fat distribution in postmenopausal females., (Copyright © 2012 Wiley Periodicals, Inc.)

Purpose: To present a novel heuristic linear mapping method to individually estimate physiological parameters for Tofts model without T(1) measurement and contrast agent concentration., Materials and Methods: A linear relationship was used for k(ep) mapping through a heuristic time intensity curve (TIC) shape factor (TSF). K(trans) maps were subsequently estimated using k(ep) maps and another approximate linear model derived from the Tofts model. Twenty-seven patients with head-and-neck squamous cell carcinoma received dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI). Physiological parameters maps were obtained using this heuristic linear mapping method and compared to the maps obtained by the normal nonlinear least-square fitting with T(1) measurement., Results: High linearity (R(2) >0.95) between k(ep) and TSF was found in all patients for k(ep) <5/min. This linearity is robust for TSF timepoint selection. The k(ep) maps generated by this linear fitting were highly consistent with those by the normal nonlinear approach (P > 0.05). The K(trans) maps were consistent with the normally derived maps in pattern distribution but the absolute value might be scaled due to the assumption of the reference K(trans) value., Conclusion: This novel method generates reliable and consistent physiological parameter maps with significantly lower computation complexity than the multiparameter nonlinear fitting. The DCE-MRI scan time can be greatly shortened without T(1) mapping., (Copyright © 2011 Wiley Periodicals, Inc.)

Purpose: To determine the optimal method to correct air and tissue susceptibility differences in the head and neck to allow proton ((1)H) chemical shift imaging (CSI) to be performed at 3T., Materials and Methods: Shimming protocols (iterative, first-order, and second-order) and perfluorocarbon (PFC) pads were evaluated using water peak linewidth measurements obtained from single-voxel magnetic resonance spectroscopy (MRS) on a head and neck phantom. After optimization of the technique, CSI was then tested on 14 patients with head and neck tumors., Results: Second-order shimming (water peak linewidth, 4.6 Hz) performed significantly (P < 0.001) better than first-order (16.5 Hz) and iterative shimming (18 Hz) and the water peak linewidth was significantly reduced using PFC pads (P < 0.001). Using second-order shimming and PFC pads, CSI was successful in 10 patients with nodal metastases (n = 8) and benign tumors (n = 2) and unsuccessful in four patients with primary tumors along the aerodigestive tract., Conclusion: Proton CSI can be successfully performed in the head and neck using second-order shimming and PFC pads to correct air and tissue susceptibility differences. CSI was more successfully performed on nodal metastases, while CSI for primary tumors along the aerodigestive tract remains a challenge., (© 2010 Wiley-Liss, Inc.)

Purpose: To determine if choline (cho) identified by proton magnetic resonance spectroscopy ((1)H-MRS) performed pretreatment and early in the course of treatment predicts clinicopathologic response of head and neck squamous cell carcinoma (HNSCC)., Materials and Methods: In all, 60 patients with HNSCC scheduled to undergo concurrent chemoradiotherapy or radiotherapy alone were recruited. (1)H-MRS was performed pretreatment and early intratreatment (2 weeks after start of treatment). Cho:creatine and cho:water ratios at each timepoint and change in the ratios between the two timepoints were correlated with locoregional failure, distant metastases, overall survival, and cancer-related death. Statistical analysis was performed using logistic regression and chi-square and a P-value of < 0.05 was considered statistically significant., Results: Cho was identified in 47/49 successful pretreatment spectra and 42 of these 47 underwent successful (1)H-MRS early intratreatment, of which 21 showed persistent cho. Locoregional failure occurred in 15, distant metastases in 6, and death in 15 patients; the follow-up period in survivors ranged from 13-64 months (mean, 39 months). No statistically significant correlation was found between (1)H-MRS parameters and clinical endpoints., Conclusion: The pretreatment cho and change in cho early during a course of treatment did not predict clinical outcome., ((c) 2010 Wiley-Liss, Inc.)

Purpose: To apply pharmacokinetic modeling to the investigation of bone perfusion in subjects of varying bone mineral density., Materials and Methods: This study re-analyzed previous experimental data. A modified pharmacokinetic model was applied to data obtained from two prior studies of dynamic contrast-enhanced MR imaging of L3 vertebral body in 165 subjects (65 males, 100 females), classified into three groups (normal, osteopenia, and osteoporosis) according to bone mineral density. Three parameters, amplitude A, exchange rate (k(ep)), and elimination rate (k(el)), were obtained by fitting the signal intensity to the pharmacokinetic model. These parameters were compared across the three groups for males and females, respectively., Results: Perfusion parameters, amplitude A was found to be reduced in osteoporotic subjects with additional, though less pronounced, reductions found in the permeability constant (A*k(ep)) and the elimination rate (k(el)). Increased marrow fat content was found in osteoporotic bone, which helped to partially explain the observed reduction in interstitial space., Conclusion: By pharmacokinetic model, bone perfusion can be quantitatively analyzed with alteration in functional parameters related to microcirculation in subjects of varying bone mineral density. Developing bone marrow specific pharmacokinetic models should help to deepen knowledge of physiological and pathological perfusion changes occurring in bone., (Copyright 2010 Wiley-Liss, Inc.)

Purpose: To determine the reproducibility of proton ((1)H) magnetic resonance (MR) spectroscopy and dynamic contrast-enhanced MR imaging in a clinical setting for the assessment of marrow fat fraction and marrow perfusion in longitudinal studies., Materials and Methods: In all, 36 subjects (17 females, 19 males, mean age 72.9 +/- 2.9 years) who underwent MR spectroscopy and/or dynamic contrast-enhanced perfusion imaging of the proximal femur were asked to return after 1 week for a repeat MR examination., Results: Reproducibility of (1)H MR spectroscopy in all bone areas tested was high, ranging from 0.78-0.85, with the highest reproducibility being in the femoral head and lowest in the femoral neck. Reproducibility of paired perfusion measurements ranged from 0.59 (enhancement slope femoral head) to 0.98 (enhancement maximum acetabulum). Overall reproducibility of (1)H MR spectroscopy and dynamic contrast-enhanced imaging tended to be best in areas with the highest inherent fat fraction or perfusion., Conclusion: Reproducibility of (1)H MR spectroscopy or perfusion imaging is sufficiently high to warrant these techniques being applied to the longitudinal study of bone diseases.

Purpose: To investigate the relationship between vertebral blood perfusion and vertebral bone mineral density (BMD) in a rat orchiectomy (ORX) model., Materials and Methods: Nine 6-month-old male Wistar-Kyoto rats were used. Computed tomography (CT) bone densitometry and dynamic MRI were performed at baseline and four weeks post-ORX. MRI was performed on a 1.5 T clinical MR scanner with a small surface coil placed under the rat lumbar spine region. A sagittal midsection of the lumbar spine was prescribed. Dynamic MRI was performed after a bolus injection of gadolinium-tetraazacyclododecane tetraacetic acid (Gd-DOTA) (0.3 mmol/kg) administered through a tail vein cannula. At a temporal resolution of 0.6 seconds, 800 images were acquired. Regions-of-interest were drawn comprising the medullary component of lumbar vertebrae L3-L6. Maximum enhancement was analyzed., Results: Satisfactory CT and MRI data for analysis was obtained in all animals. Vertebral BMD decreased by 16.6% at four weeks post-ORX (1.134 +/- 0.035 vs. 0.946 +/- 0.027 g/cm(3), P = 0.008). MRI maximum enhancement decreased by 17% at four weeks post-ORX (151.5 +/- 12.0% vs. 125.8 +/- 9.9%, P = 0.015)., Conclusion: Vertebral blood perfusion reduction is associated with vertebral BMD reduction in a male rat osteoporosis model. Perfusion MRI provides a new investigative technique for osteoporosis experimental research., ((c) 2008 Wiley-Liss, Inc.)

Purpose: To evaluate the feasibility of using a clinical 1.5T MR scanner to perform magnetic resonance (MR) diffusion tensor imaging (DTI) on in vivo rodent brains and to trace major rodent neuronal bundles with anatomical correlation., Materials and Methods: Two normal adult Sprague Dawley (SD) rats were anesthetized and imaged in a 1.5T MR scanner with a microscopic coil. DTI was performed at a resolution of 0.94 mm x 0.94 mm x 0.5 mm (reconstructed to 0.47 mm x 0.47 mm x 0.5 mm, with b-factors of 600 seconds/mm2 and 1000 seconds/mm2) and a higher resolution of 0.63 mm x 0.63 mm x 0.5 mm (reconstructed to 0.235 mm x 0.235 mm x 0.5 mm, with a b-factor of 1500 seconds/mm2). The fiber-tracking results were correlated with corresponding anatomical sections stained to visualize neuronal fibers. The apparent diffusion coefficient (ADC) and fractional anisotropy (FA) of the neuronal fibers were measured and compared with results in published reports., Results: Several major neuronal fiber tracts, including the corticospinal cord, corpus callosum, and anterior commissure, were identified in all DTI data sets. Stained anatomical sections obtained from the rats confirmed the location of these fibers. The ADC values (0.6-0.8 +/- 10(-3) mm2/second) of the fibers were similar to published figures. However, the FA values (0.3-0.35) were lower than those obtained in previous studies of white matter in rodent spinal cord., Conclusion: We have demonstrated the feasibility of using a 1.5T clinical MR scanner for neuronal fiber tracking in rodent brains. The technique will be useful in rodent neuroanatomy studies. Further investigation is encouraged to verify the FA values generated by DTI with such techniques., (Copyright 2006 Wiley-Liss, Inc.)

Purpose: To use proton magnetic resonance spectroscopy ((1)H-MRS) to evaluate vertebral marrow fat, and to determine whether bone density correlates with fat content and fat unsaturation levels in postmenopausal women., Materials and Methods: Fifty-three women (mean age = 70 years) underwent dual energy x-ray absorptiometry and (1)H-MRS, and 12 young female controls (mean age = 28 years) underwent (1)H-MRS of the lumber spine. Water and lipid peak amplitudes were measured to calculate fat content and fat unsaturation index. Spearman's correlation tests and a t-test comparison of means were applied., Results: (1)H-MRS was successful in 15 normal, 15 osteopenic, and 20 osteoporotic subjects, and in all controls. Marrow fat content was significantly elevated in osteoporotic (65.5% +/- 10%) and osteopenic (63.5% +/- 9.3%) subjects compared to normal subjects (56.3% +/- 11.2%) and young controls (29% +/- 9.6%). The fat unsaturation index was significantly decreased in osteoporotic (0.091 +/- 0.013) and osteopenic (0.097 +/- 0.014) subjects compared to normal subjects (0.114 +/- 0.016) and young controls (0.127 +/- 0.031). A good inverse correlation was observed between the fat content and the unsaturation index (r(s) = -0.53, P < 0.0001)., Conclusion: Osteoporosis is associated with increased marrow fat. As marrow fat increases, saturated lipids appear to increase preferentially to unsaturated lipids., ((c) 2005 Wiley-Liss, Inc.)

Purpose: To determine the diffusion of vertebral body marrow with quantitative MR diffusion imaging and to examine whether differences exist between subjects with postmenopausal osteoporosis and premenopausal control subjects., Materials and Methods: A total of 44 consecutive women (mean age, 70 years) with documented bone mineral density (BMD) measured by dual energy x-ray absorptiometry (T-score) and 20 normal subjects (mean age, 28 years) were examined with echo-planar diffusion imaging at 1.5 T using b values of 0, 20, 40, 60, 80, 100, 200, 300, 400, and 500 seconds/mm2. Extravascular diffusion (D) and apparent diffusion coefficient (ADC) were calculated and results from both groups compared., Results: Both D and ADC values tended to decrease with decreasing BMD. Mean D values were significantly lower in postmenopausal women with reduced BMD (0.42 +/- 0.12 x 10(-3) mm2/second) than normal premenopausal women (0.50 +/- 0.09 x 10(-3) mm2/second). Mean ADC values were significantly lower both in subjects with reduced BMD (0.41 +/- 0.10 x 10(-3) mm2/second) and normal BMD (0.43 +/- 0.08 x 10(-3) mm2/second) compared to normal controls (0.49 +/- 0.07 x 10(-3) mm2/second)., Conclusion: Accumulation of fatty bone marrow associated with osteoporosis is reflected by a decrease in D and ADC. Diffusion imaging may prove useful in the study of osteoporosis., (Copyright 2004 Wiley-Liss, Inc.)

We prospectively evaluated metabolite changes in late delayed radiation-induced injury to the temporal lobes on proton ((1)H) magnetic resonance spectroscopy (MRS) in 34 patients. Morphologically more severe injury on imaging tended to have lower N-acetyl aspartate (NAA)/creatine (Cr) and NAA/choline (Cho) ratios. A significantly higher Cho/Cr ratio was found in the most severe grade of cerebral necrosis, in which lactate might be present. The progressive decrease in NAA with increasing severity reflected neuronal loss at different stages of late delayed radiation-induced brain injury. The absence of Cho elevation in mild and moderate lesions did not suggest demyelination or glial hyperplasia as an etiologic mechanism of late delayed radiation-induced brain injury. The association of severe morphologic lesions with elevated lactate suggests ischemia as the underlying mechanism for severe lesions. (1)H MRS may provide metabolite information conducive to the understanding of the pathophysiology of late radiation-induced brain injury. J. Magn. Reson. Imaging 1999;10:130-137., (Copyright 1999 Wiley-Liss, Inc.)