M.A. Hall-Craggs

The spectrum of MRI findings in CNS cryptococcosis in AIDS

We retrospectively reviewed the cranial MRI appearances of 25 patients with AIDS and microbiologically proven central nervous system (CNS) cryptococcosis. Four patients had a normal scan. Ten patients had dilated perivascular Virchow-Robin spaces that were hyperintense on T2-weighted images. Nine of these patients developed progressive cryptococcomas, eight in the basal ganglia and one in the cerebral white matter. The cryptococcomas displayed high signal on T2-weighted and intermediate to low signal on T1-weighted images. None enhanced after dimeglumine gadopentetate. No abnormal dural or leptomeningeal enhancement was detected in any patient. One patient developed an acquired arachnoid cyst during treatment of CNS cryptococcosis which was thought to represent a focal collection of organisms and mucoid material within the subarachnoid space. In addition either cerebral atrophy and/or background white matter hyperintensity on T2-weighted images was present in 19/25 patients. In two patients the neuropathological findings at autopsy correlated well with the imaging abnormalities. In conclusion, this spectrum of MRI appearances in CNS cryptococcosis reflects the pathological mechanism of invasion by the fungus, but a normal scan or one with features of CNS HIV infection such as atrophy or white matter hyperintensity does not exclude the diagnosis.

Short echo time proton spectroscopy of the brain in HIV infection/AIDS

Short echo time proton spectra have been acquired from the brains of 30 male homosexual Acquired Immunodeficiency Syndrome (AIDS) patients and 12 age-matched control subjects on a 1.5 T MR system. The acquisition protocol used stimulated acquisition voxel localisation with a voxel size of 8 ml and repeat, echo, and mixing times of 5000, 20, and 30 ms, respectively. A single 25.6-ms Gaussian water suppression pulse was used with 128 spectral acquisitions and the data were eddy current corrected using a water reference. Baseline-corrected spectra were nonlinearly least squares fitted to a model function consisting of Gaussian functions representing the major metabolites reported in short echo proton spectra. Results indicate that the N-acetyl/creatine (NA/Cr) ratio is significantly reduced by 20% in AIDS patients [NA/Cr = 1.91 (0.51)] compared to control subjects [NA/Cr = 2.37 (0.25)] at short echo times.

Sub-cortical White-grey Matter Contrast on MRI as a Quantitative Marker of Diffuse HIV-related Parenchymal Abnormality

White matter change occurs in human immunodeficiency virus (HIV) encephalopathy, which may be difficult to assess subjectively especially in the early stages of disease. This study applies a quantitative approach to the assessment of this finding. Sixty-three HIV seropositive subjects, 47 seronegative blood donors and 17 seronegative homosexual men underwent axial T2 weighted MRI of the brain at 1.5T. Quantitative analysis was performed by obtaining the pixel contrast between parieto-occipital white matter and head of caudate grey matter (Cwg). Highest values of Cwg were found in a subgroup of subjects with AIDS who had diffuse/patchy white matter abnormalities and atrophy on qualitative image assessment. Statistically significant differences were found in Cwg between subjects with high (> or = 200 x 10(6)/I) and low (< 200 x 10(6)/I) CD4 lymphocyte counts (P < 0.05) and between subjects with and without HIV-1 associated cognitive/motor complex (P < 0.05). This technique provides an objective measure of diffuse HIV-related parenchymal abnormality seen on T2 weighted MRI.

Quantifying bone structure, micro-architecture, and pathophysiology with MRI

The radiology of bone has been transformed by magnetic resonance imaging, which has the ability to interrogate bones complex architecture and physiology. New techniques provide information about both the macrostructure and microstructure of bone ranging from micrometre detail to the whole skeleton. Furthermore functional information about bone physiology can be used to detect disease early before structural changes occur. The future of bone imaging is in quantifying the anatomical and functional information to diagnose and monitor disease more precisely. This review explores the state of the art in quantitative MRI bone imaging.