Recognizing false ischemic penumbras in CT brain perfusion studies.

Computed tomography (CT) plays a pivotal role in the diagnosis of acute stroke and in treatment decision making. CT perfusion imaging performed with intravenous iodinated contrast material allows calculation of the time to peak enhancement, mean transit time, and cerebral blood volume, important parameters for differentiating between an ischemic penumbra, which might benefit from intravascular therapy with thrombolytic agents, and infarcted tissue, which would not benefit from such therapy. Differentiation between the two entities is important because thrombolytic therapy is associated with an increased risk for intracranial hemorrhage. A finding of delay in peak enhancement or increased mean transit time in a region with normal or only slightly abnormal cerebral blood volume is suggestive of an ischemic penumbra; however, accurate interpretation of the CT perfusion parameters may be difficult in the presence of a cerebrovascular anatomic variant or physiologic condition that produces benign oligemia leading to a false appearance of penumbra. For this reason, CT perfusion parameters must be correlated with the clinical history and findings at unenhanced head CT, angiography or CT angiography, and diffusion-weighted magnetic resonance imaging. The authors identify five possible causes of false penumbras, each of which produces a different pattern at imaging: upstream flow restriction, evolution of ischemic change, vascular dysregulation, positioning of the patient's head at an angle during image acquisition, and variant anatomy in the circle of Willis. Familiarity with the imaging patterns and causes of false penumbras may increase the radiologist's confidence in diagnosis and help avoid costly errors in treatment.

Idiopathic pulmonary fibrosis: physiologic tests, quantitative CT indexes, and CT visual scores as predictors of mortality.

PURPOSE: To retrospectively evaluate quantitative computed tomographic (CT) indexes, pulmonary function test results, and visual CT scoring as predictors of mortality and to describe serial changes in quantitative CT indexes over 12 months in patients with idiopathic pulmonary fibrosis (IPF). MATERIALS AND METHODS: Institutional review board approval and informed consent were obtained at all participating institutions. One hundred sixty-seven patients (110 men, 57 women; mean age, 63 years +/- 9 [standard deviation]) with IPF were enrolled in a clinical trial. Patients underwent thin-section CT in the supine position at full inspiration at enrollment (baseline) and at 12-month follow-up. After segmentation of the lungs, mean lung attenuation (MLA), skewness, and kurtosis were measured. Extent of ground glass opacity and lung fibrosis were assessed visually. Forced vital capacity (FVC) and total lung capacity (TLC) were measured. Median duration of follow-up for mortality was 1.5 years. Univariate and multivariate survival analyses were used to determine the predictive value of baseline variables for survival. RESULTS: At univariate analysis, baseline variables predictive of death included TLC, fibrosis, skewness, and kurtosis. At multivariate analysis, FVC (P = .006) and fibrosis (P = .002) were predictors of short-term mortality. In 95 patients who had both baseline and follow-up CT scans, fibrosis (P = .030), MLA (P = .003), skewness (P < .001), and kurtosis (P < .001) all showed change indicating disease progression. CONCLUSION: Visually determined disease extent on CT images is a strong independent predictor of mortality in IPF. Serial evaluation of quantitative CT measures can show disease progression in these patients.

Multiple sclerosis pathology in the normal and abnormal appearing white matter of the corpus callosum by diffusion tensor imaging.

Lesions in the corpus callosum in multiple sclerosis (MS) include those that are hyperintense on T2-weighted images, which can be either focal (isolated) or connected, but there is evidence that the corpus callosum, similar to other white matter regions, contains normal appearing white matter (NAWM) which is abnormal based on quantitative MR methodologies. In this pilot study, diffusion tensor based measures were determined in corpus callosum from 10 patients with MS and 12 age and gender matched controls. T2-hyperintense lesions were carefully segmented out from normal appearing corpus callosum to minimize contamination of the NAWM fraction with these lesions. The orientationally averaged diffusion coefficient was increased and the fractional anisotropy reduced in the NAWM fraction of the MS patients. These results confirm prior studies which suggest that pathology in the NAWM occurs independent of focal MS lesions, and are not likely the result of sample contamination through or across slices. This injury to the NAWM may be the result of focal, microscopic T2-invisible lesions and/or secondary degeneration related to distant lesions whose related fibres cross the corpus callosum.

Quantitative CT indexes in idiopathic pulmonary fibrosis: relationship with physiologic impairment.

PURPOSE: To determine whether measurements of skewness, kurtosis, and mean lung attenuation on thin-section computed tomographic (CT) histograms in patients with idiopathic pulmonary fibrosis (IPF) correlate with pulmonary physiologic abnormality in a nonspirometrically controlled multicenter study. MATERIALS AND METHODS: The authors analyzed baseline digital thin-section CT data from 144 patients with IPF who enrolled in a double-blind placebo-controlled clinical effectiveness trial of interferon beta 1a in the treatment of IPF. All patients underwent thin-section CT in the supine position at full inspiration. The lungs were isolated by using a semiautomated thresholding technique, with an upper threshold of -200 HU. An attenuation correction algorithm was used. Pulmonary function tests (PFTs) included forced vital capacity, total lung capacity, forced expiratory volume in 1 second, and diffusing lung capacity. Univariate and multiple correlation and regression statistical analyses were used to determine relationships between histogram features and results of PFTs. RESULTS: Moderate correlations existed between histogram features and PFT results. Kurtosis showed the greatest degree of correlation with physiologic abnormality (r = 0.53, P <.01). Strength of correlation increased with exclusion of suboptimal scans but did not change significantly after application of an attenuation correction algorithm. Attenuations for lungs, gas, and soft tissue varied considerably between scanner manufacturers. Kurtosis alone provided predictions of pulmonary function that were virtually as good as those from all histogram features combined. CONCLUSION: Thin-section CT histograms of the lungs were found to correlate with results of PFTs in patients with IPF, which supports the claim that histogram features can be used as valid indexes of IPF in a multiinstitutional nonspirometrically controlled study.