Perceived Dark Rim Artifact in First-Pass Myocardial Perfusion Magnetic Resonance Imaging Due to Visual Illusion

OBJECTIVE: To demonstrate that human visual illusion can contribute to sub-endocardial dark rim artifact in contrast-enhanced myocardial perfusion magnetic resonance images.MATERIALS AND METHODS: Numerical phantoms were generated to simulate the first-passage of contrast agent in the heart, and rendered in conventional gray scale as well as in color scale with reduced luminance variation. Cardiac perfusion images were acquired from two healthy volunteers, and were displayed by the same gray and color scales used in the numerical study. Before and after k-space windowing, the left ventricle (LV)-myocardium boarders were analyzed visually and quantitatively through intensity profiles perpendicular the boarders.RESULTS: k-space windowing yielded monotonically decreasing signal intensity near the LV-myocardium boarder in the phantom images, as confirmed by negative finite difference values near the board ranging −1.07 to −0.14. However, the dark band still appears, which is perceived by visual illusion. Dark rim is perceived in the in-vivo images after k-space windowing that removed the quantitative signal dip, suggesting that the perceived dark rim is a visual illusion. The perceived dark rim is stronger at peak LV enhancement than the peak myocardial enhancement, due to the larger intensity difference between LV and myocardium. In both numerical phantom and in-vivo images, the illusory dark band is not visible in the color map due to reduced luminance variation.CONCLUSION: Visual illusion is another potential cause of dark rim artifact in contrast-enhanced myocardial perfusion MRI as demonstrated by illusory rim perceived in the absence of quantitative intensity undershoot.

Hyperperfusion in DWI Abnormality in a Patient with Acute Symptomatic Hypoglycemic Encephalopathy

The perfusion change in acute symptomatic hypoglycemic encephalopathy (ASHE) is not well known. We present the perfusion-weighted imaging of a patient with ASHE. The area of diffusion-weighted imaging abnormalities and adjacent normal-appearing white matter showed increased cerebral blood volume and flow, and shortening of time-to-peak.

Hyperperfusion in DWI Abnormality in a Patient with Acute Symptomatic Hypoglycemic Encephalopathy

The perfusion change in acute symptomatic hypoglycemic encephalopathy (ASHE) is not well known. We present the perfusion-weighted imaging of a patient with ASHE. The area of diffusion-weighted imaging abnormalities and adjacent normal-appearing white matter showed increased cerebral blood volume and flow, and shortening of time-to-peak.

Chordoid Glioma with Intraventricular Dissemination: A Case Report with Perfusion MR Imaging Features

Chordoid glioma is a rare low grade tumor typically located in the third ventricle. Although a chordoid glioma can arise from ventricle with tumor cells having features of ependymal differentiation, intraventricular dissemination has not been reported. Here we report a case of a patient with third ventricular chordoid glioma and intraventricular dissemination in the lateral and fourth ventricles. We described the perfusion MR imaging features of our case different from a previous report.

Perfusion Magnetic Resonance Imaging: A Comprehensive Update on Principles and Techniques

Perfusion is a fundamental biological function that refers to the delivery of oxygen and nutrients to tissue by means of blood flow. Perfusion MRI is sensitive to microvasculature and has been applied in a wide variety of clinical applications, including the classification of tumors, identification of stroke regions, and characterization of other diseases. Perfusion MRI techniques are classified with or without using an exogenous contrast agent. Bolus methods, with injections of a contrast agent, provide better sensitivity with higher spatial resolution, and are therefore more widely used in clinical applications. However, arterial spin-labeling methods provide a unique opportunity to measure cerebral blood flow without requiring an exogenous contrast agent and have better accuracy for quantification. Importantly, MRI-based perfusion measurements are minimally invasive overall, and do not use any radiation and radioisotopes. In this review, we describe the principles and techniques of perfusion MRI. This review summarizes comprehensive updated knowledge on the physical principles and techniques of perfusion MRI.

Cerebral Hemodynamic Analysis in Pediatric Moyamoya Patients using Perfusion Weighted MRI

OBJECTIVE: Classically, single photon emission tomography is known to be the reference standard for evaluating the hemodynamic status of patients with moyamoya disease. Recently, T2-weighted perfusion magnetic resonance(MR) imaging has been found to be effective in estimating cerebral hemodynamics in moyamoya disease. We aim to assess the utility of perfusion-weighted MR imaging for evaluating hemodynamic status of moyamoya disease. METHODS: The subjects were fourteen moyamoya patients(mean age: 7.21yrs) who were admitted at our hospital between Sep. 2001 to Sep 2003. Four normal children were used for control group. Perfusion MR imaging was performed before any treatment by using a T2-weighted contrast material-enhanced technique. Relative cerebral blood volume(rCBV) and time to peak enhancement(TTP) maps were calculated. Relative ratios of rCBV and TTP in the anterior cerebral artery(ACA), middle cerebral artery(MCA) and basal ganglia were measured and compared with those of the posterior cerebral artery(PCA) in each cerebral hemispheres. Using this data, we analysed the hemodynamic aspect of pediatric moyamoya disease patients in regarding to the age, Suzuki stage, signal change in FLAIR MR imaging, and hemispheres inducing symptoms. RESULTS: The mean rCBV ratio of ACA, MCA did not differ between normal children and moyamoya patients. However the significant TTP delay was observed at ACA, MCA territories (mean = 2.3071 sec, 1.2089 sec, respectively, p < 0.0001). As the Suzuki stage of patients is advanced, rCBV ratio is decreased and TTP differences increased. CONCLUSION: Perfusion MR can be applied for evaluating preoperative cerebral hemodynamic status of moyamoya patients. Furthermore, perfusion MR imaging can be used for determine which hemisphere should be treated, first.

Perfusion Brain Magnetic Resonance Image in Patients of Head Trauma

OBJECTIVE: The purpose of this study is to evaluate the findings of magnetic resonance(MR) perfusion study and relation with the prognosis in patients of head trauma. METHODS: Forty-two consecutive patients with head trauma were evaluated and the findings of brain computed tomography(CT) and MR image were compared with MR perfusion study. We classified perfusion MR findings into 5 categories and correlated with the prognosis. RESULTS: In all 42 patients with head trauma, 38 cases(90.5%) showed new lesions of abnormal perfusion pattern in MR perfusion study compared to CT and conventional MR image. Causes of the trauma were motor vehicle accident(73.8%) falling(16.7%), and blows to the head(7.1%) in order of frequency. The cumulative prevalent sites of focal abnormalities were frontal lobe in 11 cases(39.3%), basal ganglia and thalamus 9 cases(32.1%), temporal lobe 3 cases(10.7%) and parietal lobe 3 cases(10.7%) and occipital lobe 1 case(3.6%) and cerebellum 1 case(3.6%). The pattern of abnormalities in MR perfusion study were focal type in 18 cases(42.8%), diffuse type 18 cases(42.8%), mixed type 4 cases(9.5%). MR perfusion findings showed statistically significant correlation with initial Glasgow Coma Scale score and Glasgow Outcome Scale score(p<0.05). CONCLUSION: The patterns of perfusion MR abnormality show significant correlation with the prognosis. Further study is mandatory to define the meaning of perfusion defect area and clinical significance.

Comparison of Perfusion- and Diffusion-weighted MRI in Acute Ischemic Stroke

BACKGROUND: Perfusion imaging (PI) of magnetic resonance imaging (MRI) uses the signal loss that occurs during dynamic tracking of the first pass of intravenous paramagnetic contrast agent. Then different hemodynamic measurements can be calculated and displayed as perfusion maps. Diffusion-weighted imaging (DWI) measures diffusional movement of water molecules within the brain and it can identify acute ischemic injury or cytotoxic edema. We evaluated clinical usefulness of PI and DWI in acute ischemic stroke. METHODS: Fifteen patients with clinical diagnosis of acute cerebral infarction were imaged with PI, DWI, and magnetic resonance angiogram (MRA) including FLAIR within 24 hours after onset. Comparisons were made between infarct volumes measured by DWI and PI using the parameters including relative mean transit time (rMTT) map, relative cerebral blood volume (rCBV) map, and relative cerebral blood flow (rCBF) map. RESULTS: Two patterns were found. rMTT map in PI lesion is larger than in the DWI lesion (n=7/15), and rMTT map in PI lesion is the same size or smaller than in DWI lesion (n=8/15). The former pattern was shown in cases with severe stenosis or occlusion of the major cerebral artery (MCA, PCA, or ICA) on MRA. The majority of latter pattern was lacunes (n=6/8). Also, we found presence of infarction cores surrounded by hypoperfused areas in rMTT map in acute largearterial territorial infarction. CONCLUSIONS: Perfusion- and Diffusion- weighted MRIs may be useful in differentiating large-arterial territorial infarction from lacunes.

Findings of Perfusion MR Imaging in Acute Middle Cerebral Artery Territory Ischemic Stroke

BACKGROUND: Although a magnetic resonance imaging (MRI) is highly sensitive for changes associated with ischemic stroke, the detection of an acute ischemic lesion is usually impossible within 6 hours of the stroke onset on a conventional MRI. The perfusion MRI is a new imaging technique for diagnosing acute ischemic stroke. We evaluate the clinical usefulness of the perfusion MRI in predicting the final infarct extent in 18 patients with acute middle cerebral artery (MCA) territory ischemic stroke. METHOD: The perfusion MRI was performed within 6 hours after the stroke onset in all patients with a single-section dynamic contrast-enhanced T2*-weighted imaging in conjunction with a conventional routine MRI and MR angiography. Time-concentration curves and cerebral blood volume (CBV) maps were calculated from the dynamic MR imaging data by using numerical integration techniques. We compared findings of CBV maps with infarction on a follow-up CT or MRI. RESULTS: In 14 of 18 patients, the CBV in the occluded MCA territory were decreased. In the remaining 4 patients with a reversible ischemic neurologic deficit (RIND) or transient ischemic attack (TIA), the CBV were increased in 3 and normal in 1. Out of 14 patients with a decreased CBV, two had focal regions of increased CBV within the affected territory, indicating reperfusion hyperemia. The regions of increased or decreased CBV were eventually converted to infarction on follow-up images in all 14 patients. Out of 4 patients with RIND or TIA, one showed focal infarction in centrum semiovale on a follow-up image. CONCLUSIONS: The perfusion MRI was useful for the assessment of hemodynamic change about cerebral perfusion and may predict the extent of final infarction in acute MCA territory ischemic stroke. These results suggest that the perfusion MRI may play an important role in the diagnosis and management of acute ischemic stroke.