A grid overlay framework for analysis of medical images and its application to the measurement of stroke lesions.

OBJECTIVES: To create and evaluate an interactive software tool for measuring imaging data in situations where hand-drawn region-of-interest measurements are unfeasible, for example, when the structure of interest is patchy with ill-defined boundaries. METHODS: An interactive grid overlay software tool was implemented that enabled coding of voxels dependent on their imaging appearance with a series of user-defined classes. The Grid Analysis Tool (GAT) was designed to automatically extract quantitative imaging data, grouping the results by tissue class. Inter- and intra-observer reproducibility was evaluated by six observers of various backgrounds in a study of acute stroke patients. RESULTS: The software tool enabled a more detailed classification of the stroke lesion than would be possible with a region-of-interest approach. However, inter-observer coefficients of variation (CVs) were relatively high, reaching 70% in "possibly abnormal" tissue and around 15-20% in normal appearing tissues, while intra-observer CVs were no more than 13% in "possibly abnormal" tissue and generally less than 1% in normal-appearing tissues. CONCLUSIONS: The grid-overlay method overcomes some of the limitations of conventional Region Of Interest (ROI) approaches, providing a viable alternative for segmenting patchy lesions with ill-defined boundaries, but care is required to ensure acceptable reproducibility if the method is applied by multiple observers. KEY POINTS: Computer software developed to overcome limitations of conventional regions of interest measurements • This software is suitable for patchy lesions with ill-defined borders • Allows a more detailed assessment of imaging data.

Brain choline concentration. Early quantitative marker of ischemia and infarct expansion?

OBJECTIVE: Better prediction of tissue prognosis in acute stroke might improve treatment decisions. We hypothesized that there are metabolic ischemic disturbances measurable noninvasively by proton magnetic resonance spectroscopy ((1)H MRS) that occur earlier than any structural changes visible on diffusion-tensor imaging (DTI), which may therefore serve for territorial identification of tissue at risk. METHODS: We performed multivoxel (1)H MRS plus DTI within a maximum of 26 hours, and DTI at 3-7 days, after ischemic stroke. We compared choline, lactate, N-acetylaspartate, and creatine concentrations in normal-appearing voxels that became infarcted (infarct expansion) with normal-appearing voxels around the infarct that remained "healthy" (nonexpansion) on follow-up DTI. Each infarct expansion voxel was additionally classified as either complete infarct expansion (infarcted tissue on follow-up DTI covered > or =50% of the voxel) or partial infarct expansion (<50% of voxel). RESULTS: In 31 patients (NIH Stroke Scale score 0-28), there were 108 infarct nonexpansion voxels and 113 infarct expansion voxels (of which 80 were complete expansion and 33 partial expansion voxels). Brain choline concentration increased for each change in expansion category from nonexpansion, via partial expansion to complete expansion (2,423, 3,843, 4,158 IU; p < 0.05). Changes in lactate, N-acetylaspartate, and creatine concentrations in expansion category were insignificant although for lactate there was a tendency to such association. CONCLUSIONS: Choline concentration measurable with (1)H MRS was elevated in peri-ischemic normal-appearing brain that became infarcted by 3-7 days. The degree of elevation was associated with the amount of infarct expansion. (1)H MRS might identify DTI-normal-appearing tissue at risk of conversion to infarction in early stroke.

Clinical associations of striae gravidarum.

Striae gravidarum are a common finding in the abdominal skin of pregnant women. This study of 128 pregnant women examined factors which are associated with their occurrence. It is clear that women with higher body mass indices have more striae and that striae are also more common in younger women. These findings may be explained by the greater degrees of stretch applied to the skin in obese women with larger babies, and by changes in skin collagen and connective tissue that are age-related and affect its tendency to tear.