Biomedical subjects

Jorge Jovicich

Publications and source records attributed to Jorge Jovicich.

4 recordsLinked to original sources

PubMed2006

Reliability of MRI-derived measurements of human cerebral cortical thickness: the effects of field strength, scanner upgrade and manufacturer.

In vivo MRI-derived measurements of human cerebral cortex thickness are providing novel insights into normal and abnormal neuroanatomy, but little is known about their reliability. We investigated how the reliability of cortical thickness measurements is affected by MRI instrument-related factors, including scanner field strength, manufacturer, upgrade and pulse sequence. Several data processing factors were also studied. Two test-retest data sets were analyzed: 1) 15 healthy older subjects scanned four times at 2-week intervals on three scanners; 2) 5 subjects scanned before and after a major scanner upgrade. Within-scanner variability of global cortical thickness measurements was <0.03 mm, and the point-wise standard deviation of measurement error was approximately 0.12 mm. Variability was 0.15 mm and 0.17 mm in average, respectively, for cross-scanner (Siemens/GE) and cross-field strength (1.5 T/3 T) comparisons. Scanner upgrade did not increase variability nor introduce bias. Measurements across field strength, however, were slightly biased (thicker at 3 T). The number of (single vs. multiple averaged) acquisitions had a negligible effect on reliability, but the use of a different pulse sequence had a larger impact, as did different parameters employed in data processing. Sample size estimates indicate that regional cortical thickness difference of 0.2 mm between two different groups could be identified with as few as 7 subjects per group, and a difference of 0.1 mm could be detected with 26 subjects per group. These results demonstrate that MRI-derived cortical thickness measures are highly reliable when MRI instrument and data processing factors are controlled but that it is important to consider these factors in the design of multi-site or longitudinal studies, such as clinical drug trials.

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PubMed2005

Reliability in multi-site structural MRI studies: effects of gradient non-linearity correction on phantom and human data.

Longitudinal and multi-site clinical studies create the imperative to characterize and correct technological sources of variance that limit image reproducibility in high-resolution structural MRI studies, thus facilitating precise, quantitative, platform-independent, multi-site evaluation. In this work, we investigated the effects that imaging gradient non-linearity have on reproducibility of multi-site human MRI. We applied an image distortion correction method based on spherical harmonics description of the gradients and verified the accuracy of the method using phantom data. The correction method was then applied to the brain image data from a group of subjects scanned twice at multiple sites having different 1.5 T platforms. Within-site and across-site variability of the image data was assessed by evaluating voxel-based image intensity reproducibility. The image intensity reproducibility of the human brain data was significantly improved with distortion correction, suggesting that this method may offer improved reproducibility in morphometry studies. We provide the source code for the gradient distortion algorithm together with the phantom data.

Calibration↗

PubMed2003

Persistent brain abnormalities in antiretroviral-naive HIV patients 3 months after HAART.

BACKGROUND: Proton magnetic resonance spectroscopy (1H-MRS) and neuropsychological tests may be useful for monitoring the effectiveness of highly active antiretroviral therapy (HAART) in HIV-associated brain injury. We aimed to evaluate whether brain abnormalities will improve 3 months after HAART. METHOD: Thirty-three HIV patients naive to antiretroviral medications were evaluated before and 3 months after HAART using 1H-MRS and neuropsychological tests; results were compared with those of 26 seronegative control subjects. RESULTS: Despite significant improvement in CD4 counts, and suppression of plasma and cerebrospinal fluid (CSF) viral loads, elevated brain metabolites (choline compounds and myoinositol in the frontal lobes) and neuropsychological tests abnormalities (including the computerized tests [CalCAP]) persisted after 3 months of HAART. In the basal ganglia, choline and myoinositol became elevated only after treatment. No interaction effect was observed between the number of CSF-penetrating drugs (one vs two) and changes (baseline vs 3 months) in any of the brain metabolites, cognitive performance or CSF viral load. CONCLUSIONS: The persistent brain abnormalities suggest ongoing repair or reactive inflammatory processes in the brain after 3 months of HAART. Regimens with two CSF-penetrating antiretroviral medications do not appear to be more effective than those with one CSF-penetrating drug in treating HIV brain injury at 3 months.

AIDS Dementia Complex↗

PubMed2002

The effects of tamoxifen and estrogen on brain metabolism in elderly women.

BACKGROUND: Tamoxifen is used to treat breast cancer and may reduce the risk of breast cancer. However, there are conflicting reports as to whether tamoxifen use is associated with changes in brain metabolism and function or cognitive impairment. Consequently, we assessed the effects of tamoxifen and estrogen on the brain chemistry of elderly women. METHODS: We used proton magnetic resonance spectroscopy to measure the concentrations of N-acetyl-containing compounds, myo-inositol (MI), total creatine (creatine plus phosphocreatine), and choline-containing compounds in the frontal white matter, basal ganglia, and hippocampus of 76 elderly women of whom 16 had received tamoxifen therapy, 27 had received estrogen as hormone replacement therapy (HRT), and 33 had received neither (control group). A two-way analysis of variance (ANOVA) was performed to determine the statistical significance of differences in cerebral metabolite concentrations among subject groups and brain regions. All statistical tests were two-sided. RESULTS: Women in the tamoxifen and HRT groups had lower concentrations of MI in all areas than women in the control group (P =.02; overall group effect on ANOVA). Compared with the control group, the tamoxifen group (P =.004) and the HRT group (P =.06) had lower concentrations of MI in their basal ganglia. The MI concentration in the basal ganglia was inversely correlated with the duration of tamoxifen treatment (rho = -.72; P =.005). CONCLUSIONS: The reduced concentrations of MI in the brains of women treated with tamoxifen and HRT, compared with those of control women, suggest that tamoxifen has an effect similar to that of estrogen. These results, if confirmed, may alleviate concerns about the safety of using tamoxifen to reduce breast cancer risk in elderly women.

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