Age-Related Changes in Conventional and Magnetization Transfer MR Imaging in Elderly People: Comparison with Neurocognitive Performance

OBJECTIVE: This study was designed to compare three different measures of the elderly human brain; the magnetization transfer ratio (MTR) histogram, the percentage of brain parenchymal volume, and the volume of T2 hyperintense areas in terms of correlations with the study subjects' neurocognitive performance. MATERIALS AND METHODS: Thirty-five healthy community-dwelling elderly volunteers aged 60-82 years underwent dual fast spin-echo (FSE) imaging and magnetization transfer imaging. A semi-automated technique was used to generate the MTR histogram, the brain parenchymal volume, and the T2 lesion volume. The subjects' neurocognitive performance was assessed by using the Korean-Mini Mental State Examination (K-MMSE) and additional tests. The peak height of the MTR (PHMTR), the percentage of brain parenchymal volume (PBV), and the normalized T2 lesion volume (T2LV) were compared between the normal group (Z score on the K-MMSE > or = -2, n=23) and the mild cognitive impairment group (Z score on the K-MMSE < -2, n=12), and these parameters were correlated with age and various neurocognitive performance scores. RESULTS: The PHMTR was significantly lower in the cognitively impaired subjects than the PHMTR in the normal subjects (p = 0.005). The PBV scores were lower in the cognitively impaired subjects than in the normal subjects (p = 0.02). The T2LV scores were significantly higher in the cognitively impaired subjects (p = 0.01). An inverse correlation was found between the PHMTR and T2LV (r = -0.747, p < ; 0.001), and also between the PBV and T2LV (r = -0.823, p < ; 0.001). A positive correlation was observed between the PHMTR and the PBV (r = 0.846, p < 0.001). Scores on the various neurocognitive tests were positively correlated with the PHMTR (6 of 7 items) and the PBV (5 of 7 items), and they were negatively correlated with the T2LV (5 of 7 items). CONCLUSION: Our findings of a correlation among the PBV, the T2LV, and the PHMTR suggest that MTR histograms and the PBV and T2LV can be used as a reliable method and valid statistical tool, respectively, for quantifying the total lesion burden in an aging brain.

Comparison of Magnetization Transfer Ratios of Various Cerebral Edemas

PURPOSE: To compare magnetization transfer ratios (MTR) among various cerebral edemas with different pathophysiologic processes. MATERIALS AND METHODS: Cerebral edemas seen on MR images in 45 patients were classified as one of three types: vasogenic (n=22; tumor[n=9], contusion[n=3], hemangioma[n=4], hemorrhage[n=4], others[2]); cytotoxic (n=18; all acute infarction), and interstitial edema (n=5). In all cases, both T2-weighted images with and without magnetization transfer were obtained using off-set pulses of 600Hz. MTRs in each cerebral edema were measured and compared. RESULTS: The mean MTRs of vasogenic edema, cytotoxic edema and interstitial edema were 22 +/- 5%, 26 +/- 4 % and 19 +/- 2%, respectively. There was no statistically significant difference among the three types (p>0.05). CONCLUSION: Mean MTR was highest in cytotoxic edema and lowest in interstitial edema, but the differences were not significant.

Magnetization Transfer Ratio in Head and Neck Lymphadenopathy

PUYPOSE: The purpose of this study was to determine whether the magnetization transfer ratio(MTR) differs between malignant and benign cervical lymphadenopathy. MATERIALS AND METHODS: Magnetization transfer ratios were obtained from 104 lymph nodes of 43 patients. Fifty-five nodes were malignant and 49 were benign. Biopsy or cervical lymph node dissection was performed in 83 nodes, while the remaining 21 were diagnosed clinically or by follow-up imaging studies. Among the 55 malignant nodes, squamous cell carcinomas accounted for 29 cases, lymphomas for 15, undifferentiated carcinomas for four, acute myelogenous leukemia for four, and melanomas for three. The 49 benign nodes comprised 21 cases of reactive hyperplasia, 12 of Kikuchi's disease, nine of acute lymphadenitis, and seven of tuberculous lymphadenitis. All scans were performed using a 1.5T Magnetom Vision(Siemens, Erlangen, Germany) with phased-array or Helmholtz-type neck coil. Scanning was performed with and without magnetization transfer pulse(MT pulse : 11.2 T, 250 Hz band-width, off-set 2.0 KHz) using FLASH 2D sequencing. The region of interest(ROI) for signal intensity(SI) measurements was sampled at the same nodes by keeping the position, shape and size of the ROI constant for the scans before and after the MT pulse was applied. SI measurements were repeated more than three times in each node and the mean value was used to calculate MTR. In this study, however, corrected MTRs(CoMTRs) were used for correction of the effect of background noise produced by magnetic field inhomogeneity. RESULTS: Mean CoMTRs of malignant and benign nodes were 0.33(SD: +/- 0.04) and 0.28(SD: +/- 0.05), respectively. This difference was statistically significant. At CoMTR 0.31, the sensitivity and specificity of malignant nodes were 83% and 75%, respectively. CONCLUSION: A CoMTR of above 0.31 suggests malignant lymphadenopathy. CoMTR is one of the MR criteria which can serve to differentiate between malignant and benign lymphadenopathy.

Magnetization Transfer on T2-weighted Image: Magnetization Transfer Ratios in Normal Brain and CerebralLesions

PURPOSE: To evaluate the magnetization transfer ratio(MTR) of various normal structures and pathologiclesions, as seen on magnetization transfer T2-weighted images (MT+T2WI). MATERIALS AND METHODS: In ten normalvolunteers, T2-weighted images without MT (MT-T2WI) and with MT(MT+T2WI) were obtained. Off-set pulses used inMT+T2WI were 400, 600, 1000, 1500, and 2000Hz. In 60 clinical cases infarction(n=10), brain tumors(n=5), traumatichematomas(n=5), other hematomas(n=3) vascular malformation(n=2) white matter disease(n=2) normal(n=31) andothers(n=2), both MT-T2WI and MT+T2WI images were obtained using an off-set pulse of 600 Hz. In all volunteers andpatients, MTR in various normal brain parenchyma and abnormal areas was measured. RESULT: The MTRs of white andgray matter were 48% and 45% respectively at 400 Hz, 26% and 22% at 600Hz, 12% and 11% of 1000Hz, 10% and 9% 1500HZ, and 9% and 8% at 2000Hz of RF. The MTR of CSF was 43% at 400 Hz of off-resonance RF, while the contrastresolution of T2WI was poor. An off-resonance of 600Hz appeared to be the optimal frequency. In diseased areas,MTRs varied but were usually similar to or lower than those of brain parenchyma. CONCLUSION: The optimaloff-resonance RF on MT+T2WI appears to be 600 Hz for relatively high MTR of brain parenchyma and low MTR of CSF,in which MTRs of white and gray matter were 26% and 22%, respectively, of 600Hz off-set pulse. The MTRs ofcerebral lesions varied and further studies of various cerebral lesions are needed.

Contrast-Enhanced Turbo Spin-Echo(TSE) T1-weighted Imaging: Improved Contrast of Enhancing Lesions

PURPOSE: The purpose of this study was to evaluate the effect of contrast improvement of enhancing brain lesions by inherent magnetization transfer effect in turbo spin-echo (TSE) T1-weighted MR imaging. MATERIALS AND METHODS: Twenty-six enhancing lesions of 19 patients were included in this study. Using a 1.0T superconductive MR unit, contrast-enhanced SE T1-weighted images (TR=600 msec, TE=12 msec, NEX=2, acquisition time=4 min 27sec) and contrast-enhanced TSE T1-weighted images (TR=600 msec, TE=12 msec, NEX=2, acquisition time=1min 44sec) were obtained. Signal intensities at enhancing lesions and adjacent white matter were measured in the same regions of both images. Signal-to-noise ratio (SNR) of enhancing lesions and adjacent white matter, and contrast-to-noise ratio (CNR) and lesion-to-background contrast (LBC) of enhancing lesions were calculated and statistically analysed using the paired t-test. RESULTS: On contrast-enhanced TSE T1-weighted images, SNR of enhancing lesions and adjacent white matter decreased by 18%(p<0.01) and 32% (p<0.01), respectively, compared to contrast-enhanced SET1-weighted images. CNR and LBC of enhancing lesions increased by 16% (p<0.05) and 66% (p<0.01), respectively. CONCLUSION: Due to the proposed inherent magnetization transfer effects in TSE imaging, contrast-enhanced T1-weighted TSE images demonstrated a statistically significant improvement in CNR and LBC, compared to conventional contrast-enhanced T1-weighted SE images, and scan time was much shorter.

Effects of Magnetization Transfer in Gadolinium-Enhanced Brain MR Imaging

PURPOSE: To evaluate the effect of magnetization transfer(MT) in contrast-enhanced brain MR imaging of the various intracranial diseases. MATERIALS AND METHODS: We prospectively studied the effect of MT incontrast-enhanced brain MR imaging 101 patients with a variety of intracranial diseases. In all patients contrast-enhanced T1-weighted(TR/TE = 550/14) SE MR images with and without MT were obtained on a 1.5 Tsuper conducting unit(Magnetom, Siemens). The MT pulse used for MT images was an 8.1 msec(=250 Hz band width) syncpulse, 1000 Hz off-resonance. We randomly divided the patients into two groups : group I and group II. Group I consisted of 54 patients in whom contrast-enhanced images without MT and then images with MT were obtained just ofter the injection of Gd-DTPA(0.1 mmol/kg). In group II(47 patients), contrast-enhanced images with MT and then the images without MT were obtained, considering the delayed-enhancement effect. The effect of MT was assessed visually and quantitatively. For quantitative assessment, contrast to noise ratios(CNR) were calculated in 27 cases with enhancing intracranial tumors larger than 1 cm. We then compared CNRs of contrast-enhanced images with and without MT. The paired t-test was used for statistical analysis. RESULTS: On visual assessment, only11.9%(12/101) of normally enhancing structures and only 20.3%(14/69) of enhancing lesions showed improved enhancement in images with MT. There was however, no case in which the enhancing lesion was seen only in MR image with MT but not in that without MT. On quantitative analysis there was no statistically significant difference between overall images with MT and those without MT(p>0.05). The average CNR of images with MT was higher than that of images without MT in group I, but not in group II. CONCLUSION: MT in contrast-enhanced brain MR imaging resulted in contrast improvement in a limited number(less than approximately 20%) of patients. Routine application of MT images to contrast-enhanced brain MR imaging may be of limited value. Further studies on the clinical usefulness of MT technique with more refined MT pulse are thus needed.