Henry Z. Wang

Dual-Energy CT Angiography in the Evaluation of Intracranial Aneurysms: Image Quality, Radiation Dose, and Comparison With 3D Rotational Digital Subtraction Angiography

OBJECTIVE The purpose of this study was to evaluate the image quality, radiation dose, and diagnostic accuracy of dual-energy CT angiography (CTA) compared with 3D rotational digital subtraction angiography (DSA) in the detection of intracranial aneurysms. SUBJECTS AND METHODS Forty-six patients with clinically suspected intracranial aneurysms underwent dual-source dual-energy CTA and 3D DSA. For the analysis of the image quality and radiation dose of dual-energy CTA, 46 patients who underwent digital subtraction CTA were recruited as a control group. The image quality of dual-energy CTA and digital subtraction CTA was rated on a 4-point scale as excellent, good, moderate, or poor. The radiation dose of CTA was recorded according to patient protocol. Aneurysm detection with dual-energy CTA compared with 3D DSA was analyzed on a per-patient and on a peraneurysm basis. Sensitivity, specificity, and positive and negative predictive values for aneurysm presence were determined. The mean maximum diameter and dome and neck dimensions of aneurysms were measured on dual-energy CTA and 3D DSA images. Correlation analysis between the two techniques was performed. RESULTS There was no statistical difference between the image quality of dual-energy CTA and that of digital subtraction CTA (p>0.05). Patients undergoing dual-energy CTA received a smaller radiation dose (volume CT dose index, 20.6+/-0.1 mGy [mean+/-SD]; dose-length product, 398.6+/-19.0 mGy x cm) than those undergoing digital subtraction CTA (volume CT dose index, 50.4+/-3.4 mGy; dose-length product, 1,095.6+/-114.2 mGyxcm) (p<0.05). Three-dimensional DSA showed no aneurysm in 11 patients and 40 aneurysms in 35 patients. The mean maximum diameter of the aneurysms was 6+/-3 mm; the dome measurement, 5+/-3 mm; and the neck dimension, 3+/-2 mm. With dual-energy CTA, 38 aneurysms in 34 patients were correctly detected, and two aneurysms in two patients were missed. With DSA as the standard of reference, the sensitivity, specificity, and positive and negative predictive values of dual-energy CTA in the detection of intracranial aneurysm were 97.1%, 100%, 100%, and 91.7% on a per-patient basis and 95.0%, 100%, 100%, and 99.7% on a per-aneurysm basis. Dual-energy CTA had sensitivities of 93.8%, 100%, and 80.0% and specificities of 100%, 100%, and 100% in the detection of aneurysms larger than 5 mm, those measuring 3.1-5 mm, and aneurysms 3 mm or smaller. At dual-energy CTA, the mean maximum diameter and dome and neck dimensions were 6+/-3 mm, 5+/-3 mm, and 3+/-2 mm. Excellent correlation was found between DSA and dual-energy CTA findings with respect to mean maximum diameter and dome and neck dimensions (r=0.969, 0.957, and 0.870; p = 0.000). CONCLUSION On the basis of the findings in the small series of patients evaluated, contrast-enhanced dual-energy CTA had diagnostic image quality at a lower radiation dose than digital subtraction CTA and high diagnostic accuracy compared with 3D DSA in the detection of intracranial aneurysms.

Diffusion-weighted MR imaging of posterior reversible leukoencephalopathy syndrome: A pictorial essay

Posterior reversible leukoencephalopathy syndrome is characterized by reversible white matter lesions. However, ischemic injury with irreversible damage may occur. This pictorial essay illustrates MR features associated with posterior reversible leukoencephalopathy syndrome. We will emphasize the role of diffusion-weighted imaging for the discrimination of irreversible ischemic injury from reversible vasogenic edema.

CNS vasculitis and vasculopathy:Efficacy and usefulness of diffusion-weighted echoplanar MR imaging

This pictorial essay illustrates the usefulness of diffusion-weighted imaging (DWI) on various vasculitis or vasculopathies, including systemic lupus erythematosus (SLE), Behçets disease, Churg-Strauss disease, primary angitis of the central nervous system (PACNS), giant cell arteritis, infectious vasculitis, sickle cell disease, drug-induced vasculopathy and hypertensive vasculopathy. DWI proves to detect small and active ischemic changes not visible on conventional MRI, and it clearly discriminates cytotoxic from vasogenic edema in patients with cerebral vasculitis or vasculopathy. DWI seems useful in assessing the treatment and patient outcome.

Brain MR Imaging in the Evaluation of Chronic Headache in Patients without Other Neurologic Symptoms

RATIONALE AND OBJECTIVES The authors investigated the use of magnetic resonance (MR) imaging of the brain in adult patients with a primary complaint of chronic headache and no other neurologic symptoms or findings and determined the yield and MR predictors of major abnormalities in these patients. MATERIALS AND METHODS The medical records and MR images of 402 adult patients with chronic headache were retrospectively reviewed. All patients had been evaluated and referred by the neurology service. The findings were categorized as either negative or positive for major abnormality. Multivariate analysis with a linear logistic regression technique was performed on the clinical data, which included patient age, patient sex, and headache type. RESULTS Major abnormalities were found in 15 patients (3.7%), consisting of seven women (2.4%) and eight men (6.9%). Major abnormalities were found in 0.6% of those with migraine headaches, 1.4% with tension headaches, none with mixed migraine and tension headaches, 14.1% with atypical headaches, and 3.8% with other types of headaches. Multivariate analysis showed that the atypical headache type was the most significant predictor of major abnormality. CONCLUSION The yield of major abnormalities found with brain MR imaging in patients with isolated chronic headache is low. However, those patients with atypical headaches have a higher yield of major abnormalities and may benefit from imaging.

An analysis of noise propagation in computed T2, pseudodensity, and synthetic spin-echo images.

Methods are reviewed for estimating the transverse relaxation time T2 and the pseudodensity (PD) from spin-echo measurements acquired at an arbitrary set of echo times [TEi]. Least-squares fitting is applied to the logarithmically processed signals for the case in which the weights are proportional to the inverse of the logarithmically transformed signal variances (the minimum variance case). General formulas are derived for the estimated noise levels in the PD and T2 estimates due to the propagation of uncertainties in the original measurements. It is shown that the T2 and PD estimates are anticorrelated. Additionally, an expression is derived for the variance in a synthetic spin-echo signal subsequently formed from the PD and T2 estimates. It is shown that under many circumstances a signal synthesized at some echo time can have a signal-to-noise ratio superior to that in a signal directly acquired at that time. Experimental measurements made on phantoms match the theoretical predictions to a high degree.

Diffusion-weighted echo-planar MR imaging of CNS involvement in systemic lupus erythematosus

RATIONALE AND OBJECTIVES The purpose of this study was to determine the range of findings at diffusion-weighted magnetic resonance (MR) imaging in patients with systemic lupus erythematosus (SLE) and central nervous system involvement. MATERIALS AND METHODS Diffusion-weighted MR images were reviewed in 20 patients with SLE and correlated with clinical symptoms and findings at computed tomography, conventional MR imaging, MR angiography, or conventional angiography. RESULTS Diffusion-weighted MR imaging showed acute or subacute lesions in nine of 20 patients (45%). In the other 11, it showed no abnormal findings or chronic lesions. In four of the nine patients with lesions, diffusion-weighted imaging primarily showed hyperintense lesions with decreased apparent diffusion coefficient (ADC), which indicates acute or subacute infarcts. In four other patients, it primarily showed iso- or slightly hyperintense lesions with increased ADC, suggesting vasogenic edema. In two of these four patients, the findings were consistent with hypertensive encephalopathy. In the other two, small hyperintense foci on diffusion-weighted images with decreased ADC were seen within the vasogenic edema. These foci presumably represent microinfarcts associated with SLE vasculopathy. In the ninth patient, diffusion-weighted imaging showed a small linear hyperintense lesion with normal ADC in the left parietooccipital region. CONCLUSION Diffusion-weighted imaging shows primarily two patterns of acute or subacute parenchymal lesions in patients with SLE: acute or subacute infarction and vasogenic edema with or without microinfarcts.

Diffusion-weighted echo-planar MR imaging: clinical applications and pitfalls. A pictorial essay

Diffusion-weighted imaging (DWI) provides unique information about various pathological changes of the brain. DWI is sensitive for the detection of hyperacute infarcts, and useful in distinguishing acute or subacute infarcts from chronic infarcts. DWI is useful in differentiating cytotoxic edema from vasogenic or interstitial edema, which may help to determine prognosis. DWI is useful in differentiating cystic or necrotic tumors from abscesses or epidermoids. DWI can discriminate nonenhanced tumor infiltration from vasogenic edema, and differentiate dysmyelination from demyelination.

Improved precision in calculated T1 MR images using multiple spin-echo acquisition.

Calculated T1 images require that magnetic resonance signals be detected at several inversion or repetition times (TR). Multiple spin-echo (SE) acquisitions provide several measurements of the magnetization at each TR, the signal size diminishing according to T2 decay. In this work we review one method (Case 1) for estimating T1 from single echoes and present four new methods (Cases 2-5) in which multiple acquired echoes are used. For Case 2 a fit is performed using the first echo at each TR, repeated using second echoes, etc., and the final T1 estimate is the simple average of the individual fits at each echo time (TE). For Case 3 the optimum weighted average is performed. For Cases 4 and 5 synthetic SE images are generated at each TR prior to the T1 fit, Case 4 using a synthetic TE of zero, and Case 5 using a TE providing maximum signal-to-noise ratio in the synthetic image. The relative precision in T1 provided by each method is calculated rigorously. It is proven that Cases 3 and 5 are optimum and equivalent and can theoretically reduce the noise in T1 images by as much as 40% over Case 1 with no increase in scanning time. Approximations are proposed that enable the optimum methods to be implemented in a practical fashion. Experimental images are presented that verify the relative predicted behavior.

Correlation of Diffusion and Perfusion MRI With Ki-67 in High-Grade Meningiomas

OBJECTIVE Atypical and anaplastic meningiomas have a greater likelihood of recurrence than benign meningiomas. The risk for recurrence is often estimated using the Ki-67 labeling index. The purpose of this study was to determine the correlation between Ki-67 and regional cerebral blood volume (rCBV) and between Ki-67 and apparent diffusion coefficient (ADC) in atypical and anaplastic meningiomas. MATERIALS AND METHODS A retrospective review of the advanced imaging and immunohistochemical characteristics of atypical and anaplastic meningiomas was performed. The relative minimum ADC, relative maximum rCBV, and specimen Ki-67 index were measured. Pearsons correlation was used to compare these parameters. RESULTS There were 23 cases with available ADC maps and 20 cases with available rCBV maps. The average Ki-67 among the cases with ADC maps and rCBV maps was 17.6% (range, 5-38%) and 16.7% (range, 3-38%), respectively. The mean minimum ADC ratio was 0.91 (SD, 0.26) and the mean maximum rCBV ratio was 22.5 (SD, 7.9). There was a significant positive correlation between maximum rCBV and Ki-67 (Pearsons correlation, 0.69; p = 0.00038). However, there was no significant correlation between minimum ADC and Ki-67 (Pearsons correlation, -0.051; p = 0.70). CONCLUSION Maximum rCBV correlated significantly with Ki-67 in high-grade meningiomas.

Association of CT Perfusion Parameters with Hemorrhagic Transformation in Acute Ischemic Stroke

Because hemorrhagic transformation affects treatment and patient prognosis, these authors explored whether CT perfusion predicts it. Twenty percent of their subjects developed hemorrhagic transformation and these patients did not differ from controls in terms of age, gender, time to presentation, or comorbidities. Only CBV was found to be lower and predictive of hemorrhagic transformation. BACKGROUND AND PURPOSE: Prediction of hemorrhagic transformation in acute ischemic stroke could help determine treatment and prognostication. With increasing numbers of patients with acute ischemic stroke undergoing multimodal CT imaging, we examined whether CT perfusion could predict hemorrhagic transformation in acute ischemic stroke. MATERIALS AND METHODS: Patients with acute ischemic stroke who underwent CTP scanning within 12 hours of symptom onset were examined. Patients with and without hemorrhagic transformation were defined as cases and controls, respectively, and were matched as to IV rtPA administration and presentation NIHSS score (± 2). Relative mean transit time, relative CBF, and relative CBV values were calculated from CTP maps and normalized to the contralateral side. Receiver operating characteristic analysis curves were created, and threshold values for significant CTP parameters were obtained to predict hemorrhagic transformation. RESULTS: Of 83 patients with acute ischemic stroke, 16 developed hemorrhagic transformation (19.28%). By matching, 38 controls were found for only 14 patients with hemorrhagic transformation. Among the matched patients with hemorrhagic transformation, 13 developed hemorrhagic infarction (6 hemorrhagic infarction 1 and 7 hemorrhagic infarction 2) and 1 developed parenchymal hematoma 2. There was no significant difference between cases and controls with respect to age, sex, time to presentation from symptom onset, and comorbidities. Cases had significantly lower median rCBV (8% lower) compared with controls (11% higher) (P = .009; odds ratio, 1.14 for a 0.1-U decrease in rCBV). There was no difference in median total volume of ischemia, rMTT, and rCBF among cases and controls. The area under the receiver operating characteristic was computed to be 0.83 (standard error, 0.08), with a cutoff point for rCBV of 1.09. CONCLUSIONS: Of the examined CTP parameters, only lower rCBV was found to be significantly associated with a relatively higher chance of hemorrhagic transformation.