Perfusion-weighted MR Imaging Research Articles

Magnetic resonance imaging in perinatal brain injury: clinical presentation, lesions and outcome

Neonatal MR imaging is invaluable in assessing the term born neonate who presents with an encephalopathy. Successful imaging requires adaptations to both the hardware and the sequences used for adults. The perinatal and postnatal details often predict the pattern of lesions sustained and are essential for correct interpretation of the imaging findings, but additional or alternative diagnoses in infants with apparent hypoxic ischaemic encephalopathy should always be considered. Perinatally acquired lesions are usually at their most obvious between 1 and 2 weeks of age. Very early imaging (<3 days) may be useful to make management decisions in ventilated neonates, but abnormalities may be subtle at that stage. Diffusion-weighted imaging is clinically useful for the early identification of ischaemic white matter in the neonatal brain but is less reliable in detecting lesions within the basal ganglia and thalami. The pattern of lesions seen on MRI can predict neurodevelopmental outcome. Additional useful information may be obtained by advanced techniques such as MR angiography, venography and perfusion-weighted imaging. Serial imaging with quantification of both structure size and tissue damage provides invaluable insights into perinatal brain injury.

Prognostic value of perfusion-weighted imaging in brain glioma: a prospective study

Biopsy targeting based on MR imaging alone may fail to identify malignant areas in brain gliomas. Considering the differences in relative Cerebral Blood Volume (rCBV) ratios reported among tumour grades, we evaluated whether perfusion-weighted MR imaging (PWI) could usefully implement the routine preoperative imaging by detecting those areas bearing a higher yield for malignancy to guide the stereotactic biopsy or the surgical removal. We studied a series of 55 consecutive patients with newly diagnosed brain glioma using both conventional MR imaging and PWI in the preoperative assessment. The pathological diagnosis was established by stereotactic biopsy in 29 cases and by craniotomy in 24 cases. We evaluated the patient survival to detect undergrading. Independent from contrast-enhancement, perfusion-weighted MR imaging improved the target selection in stereotactic biopsy guidance and the removal of malignant areas in tumours amenable to surgery. Particularly sensitive to the perfused part of the tumour as to small regional changes, rCBV maps allowed a better detection of malignant areas. The rCBV ratios correlated significantly to the tumour grade and the final outcome (p < 0.01). We found PWI valuable in the preoperative assessment of brain gliomas, discriminating high from low-grade gliomas. PWI can easily be performed on widely available MR imaging systems as part of the routine imaging of gliomas.

Dynamic susceptibility contrast perfusion imaging of cerebral ischemia in nonhuman primates: Comparison of Gd‐DTPA and NMS60

To study a new gadolinium (Gd) contrast agent-NMS60-for MR perfusion-weighted imaging (PWI) of brain tissue. NMS60 is a Gd3+ trimer with a molecular weight of 2158 Daltons, and a T2 relaxivity almost three times higher than that of Gd-DTPA. Middle cerebral artery (MCA) occlusion was induced in nine nonhuman primates. The animals were scanned acutely and for up to six follow-up time points. PWI peak, and time-to-peak maps were generated, and perfusion deficit volumes were measured from these maps. The values of peak, time-to-peak, and perfusion deficit volume were compared between NMS60 and GD-DTPA. These results demonstrate that there was no significant difference in our calculated perfusion parameters between the two contrast agents. The two agents were found to be equally effective for PWI for acute and chronic stroke in primates. Along with its previously demonstrated advantage for T1-enhanced imaging, the current results show that NMS60 is a viable contrast agent for use in stroke patients.

SU‐EE‐A4‐01: Regional Change in Brain Perfusion, in Irradiated Normal Tissue: Correlation Study Between Perfusion MRI and Spatial Distribution of Radiation Dose Delivered

Purpose: When irradiating the normal brain, one of the principal causes of complications is damage to the cerebral vasculature, particularly the micro‐vasculature. This is of particular concern when treating diseases which are slow‐growing or are not malignant. While there is some data relating loss of perfusion to radiation dose in other tissues such as lung, there is very little data for the brain. We intend to determine the relationship between the change due to irradiation in hemodynamic measures, such as relative regional Mean Transit Time (rrMTT) and relative regional Cerebral Blood Volume (rrCBV), and the radiation dose delivered to the normal brain tissue. Method and Materials: We acquired data in the form of perfusion weighted images (PWI) for two patients. We used a 3.0 T magnet at the Seaman Family MRI Centre at the Foothills Medical Centre and a single‐shot echo‐planar imaging (EPI) sequence following the injection of a paramagnetic contrast agent (Gd‐DTPA‐Magnevist; Berlex, Wayne, NJ). These images have been processed to yield rrCBV and rrMTT. The patients had previously been treated with surgery, but had received no chemotherapy. Results: Our preliminary results show that with a follow‐up time of 4 months after receiving approximately 5000 cGy/25 fractions, in normal brain tissue the rrMTT is reduced by approximately 2% (1.8 ± 0.5) and the rrCBV is reduced by almost 12% (11.8 ± 2.2). The tumor showed reductions in both rrMTT (1.2 ± 1.5)% and rrCBV (19.9 ± 3.5)%. It is expected that these changes will increase with longer term follow‐up. Conclusion: Perfusion Weighted MR Imaging can be used to assess the change in hemodynamic measures in the normal brain tissue after radiotherapy.

Role of Diffusion and Perfusion-Weighted MR Imaging in Differentiating Meningioma from Solitary Dural Metastasis

In some instances conventional imaging techniques fail to differentiate meningiomas from isolated dural metastasis. This study aimed to evaluate the role of diffusion and perfusion-weighted MRI in differentiating meningiomas and dural metastasis. In this study, 14 metastasis and 26 meningiomas were involved. The imaging characteristics were analyzed using conventional MRI. Diffusion-weighted MRI was performed and ADC values were calculated from the solid components and the peritumoral edema. Perfusion-weighted MRI was performed and relative cerebral blood volume (rCBV) was calculated. Student's t test was used for the statistical analysis. Dural metastasis and meningiomas could not be differentiated by qualitative assessment of conventional and diffusion-weighted MRI. The mean intratumoral and peritumoral ADC values were not statistically significant (p &gt; 0.05). The rCBV ratios for dural metastasis and meningiomas were 4.13 ± 2.32 and 7.32 ± 4.10 respectively and the difference between two was statistically significant (p = 0.003). Peritumoral rCBV ratios for dural metastasis and meningiomas were not statistically significant (p &gt; 0.05). Conventional MRI findings of dural metastasis and meningiomas may overlap in some lesions. In differentiation of these lesions diffusion-weighted MRI yields no further information additional to conventional sequences. Perfusion-weighted MRI can be useful to distinguish these lesions by demonstrating high intratumoral rCBV ratios for meningiomas and low rCBV ratios for metastasis.

Complete recovery after spontaneous thrombolysis of a middle cerebral artery embolism: An imaging report

A 53-year-old-man demonstrated an embolism of the left middle cerebral artery, a rapid spontaneous thrombolysis and a subsequent recovery of the cerebral perfusion. These events were documented using MR angiography, perfusion-weighted MR imaging and digital subtraction angiography. The patient recovered consciousness and his symptoms of right hemiparesis and aphasia disappeared completely, representing the so-called spectacular shrinking deficit. This case provides evidence that an early spontaneous thrombolysis may recover cerebral perfusion and alleviate the symptoms of the patient.

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MR perfusion-weighted imaging and quantitative analysis of cerebral hemodynamics with symptom provocation in unmedicated patients with obsessive–compulsive disorder

We evaluated the potential effectiveness of dynamic contrast-enhanced perfusion-weighted images (PWI) in determining hemodynamic activation in brain structures that may be involved in mediating the symptomatology of patients with obsessive–compulsive disorder (OCD), as manifested by contamination obsessions with washing compulsions. Ten unmedicated female patients with OCD were subjected to PWI, and relative cerebral blood flow (rCBF) in each region of interest (ROI) and self-ratings of OCD symptoms were compared before and after symptom provocation. We found that increases in the Anxiety Analogue Scale (AAS) and OCD Analogue Scale (OCDAS) scores were each significantly associated with provocation. The correlations between OCDAS and AAS scores were also statistically significant during both the control and provoked conditions. Compared with the control state, there was a significant increase in rCBF during the symptomatic state in the right head of caudate nucleus, thalamus, and bilateral orbitofrontal cortices (OFC). No statistical changes in rCBF were found in the bilateral anterior cingulate cortices (ACC). These findings demonstrate that OCD symptomatology is accompanied by anxiety, and that abnormal features are particularly apparent in the orbitofrontal-subcortical circuits.

Functional evaluation of normothermic ischemia and reperfusion injury in dog kidney by using MR perfusion-weighted imaging

目的 结合病理对照研究MR灌注成像评价犬肾缺血再灌注损伤后肾功能的变化.方法雄性家犬12只随机分成4组,分别结扎左侧肾动脉30、60、90和120 min,开放后再灌注损伤1 h.MR检查选择5个时间段,即动脉结扎前、动脉结扎后即刻、动脉开放前、动脉开放后即刻和再灌注损伤后,分别进行常规T2WI和(或)重T2WI(T2*WI)[包括:真实稳态进动快速成像(true-FISP),快速自旋回波(TSE),平面回波成像(EPI)]和T1WI,最后进行灌注加权成像(PWI)[采用反转恢复快速小角度激发(IR-turbo-FLASH)序列]检查.测量肾皮层(C)、外髓层(OM)和内髓层(IM)的信号强度值(SI),比较不同时间段肾脏各层之间的信号变化,并绘制信号强度与时间关系曲线(SI-T曲线).选择曲线峰值(P)、达峰时间(Tp)和曲线下面积(A)作半定量分析.结果动脉结扎后,在T2WI、T2*WI上左肾各层信号明显下降;动脉开放后,EPI各组中左肾OM和IM信号仍明显低于右肾.右肾各层SI-T曲线清晰显示三期增强方式,而左肾OM和IM均表现为单期增强,无明显的增强峰出现,且曲线下面积较右肾明显减低.结论PWI能较准确地评价缺血再灌注损伤后肾功能的变化。

Validation of the CBF, CBV, and MTT values by perfusion MRI in chronic occlusive cerebrovascular disease: A comparison with 15O-PET 1

Rationale and objectives To evaluate the reliability of cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT) values obtained by deconvolution algorithm perfusion-weighted MR imaging (D-PWI), we compared these values with those obtained by first-moment algorithm perfusion-weighted MR imaging (F-PWI) and 15O-PET. Subjects and methods Six healthy volunteers and eleven patients with chronic occlusive cerebrovascular disease were studied with both perfusion-weighted MR imaging and 15O-PET, and region-of-interest analyses were performed. Normalization factors for CBF and CBV values obtained by D-PWI were determined as the mean values of 15O-PET divided by those of D-PWI in healthy volunteers. Then these values were used in analyzing the data of the patients. Results The MTT value obtained by D-PWI was 6.1 ± 0.5 seconds on the non-occluded side, 6.4 ± 0.7 seconds on the minimally to moderately stenosed side, and 6.7 ± 1.2 seconds on the severely stenosed to occluded side. These values were significantly correlated with those obtained by F-PWI ( r = 0.83; P < .001), and with those obtained by 15O-PET ( r = 0.78; P < .05). However, the CBF and CBV values obtained by D-PWI did not correlate with those obtained by 15O-PET. Conclusion MTT values obtained by D-PWI were reliable parameters of cerebral hemodynamics, but the CBF and CBV values obtained by D-PWI were not always reliable.

Reliability of mean transit time obtained using perfusion-weighted MR imaging; comparison with positron emission tomography

The purpose of this project was to assess the reliability of the cerebral mean transit time (MTT) obtained using perfusion-weighted MR imaging by comparing it with the MTT obtained when performing positron emission tomography (PET). Ten patients with chronic occlusive cerebrovascular disease were investigated. They had either unilateral internal carotid artery occlusion or middle cerebral artery occlusion. The regions-of-interest were placed in non-infarcted areas within the territory of the middle cerebral artery on the affected side. Control regions-of-interest were placed in mirrored regions of the contralateral side. Linear regression analyses were performed using the parameters of the MTT obtained with perfusion-weighted MR imaging and the MTT, cerebral blood flow, vascular reactivity, and oxygen extraction fraction obtained with PET. The respective MTTs of the affected and non-affected sides obtained with perfusion-weighted MR imaging versus those with PET were 7.3 ± 2.2 s and 6.0 ± 1.2 s versus 8.2 ± 3.0 s and 6.4 ± 1.7 s. The MTT obtained using perfusion-weighted MR imaging and PET demonstrated statistically significant correlation ( r = 0.87, p < 0.0001). The MTT obtained with perfusion-weighted MR imaging correlated statistically with cerebral blood flow ( r = −0.74, p < 0.001), vascular reactivity ( r = −0.73, p < 0.001) and oxygen extraction fraction ( r = 0.61, p < 0.01). Similarly, the MTT obtained using PET statistically correlated with cerebral blood flow ( r = −0.78, p < 0.0001), vascular reactivity ( r = −0.51, p < 0.05) and oxygen extraction fraction ( r = 0.68, p < 0.01). The reliability of the MTT obtained using perfusion-weighted MR imaging appears to be approximately equal to that obtained with positron emission tomography.

Peritumoral brain edema in intracranial meningiomas evaluated by dynamic perfusion-weighted MR imaging: a preliminary study.

Our objective was to semi-quantitatively evaluate the cerebral perfusion in the peritumoral brain edema of meningiomas using dynamic perfusion-weighted MR imaging. Six patients with intracranial meningiomas accompanied by peritumoral brain edema were prospectively examined by perfusion-weighted MR imaging. One patient was examined twice, once before and once 5 months after the surgical resection. The relative regional cerebral blood volume (rrCBV), the relative regional cerebral blood flow (rrCBF), and the relative regional mean transit time (rrMTT) were calculated for peritumoral brain edema and the contralateral white matter. These parameters were compared between peritumoral brain edema and the contralateral white matter. The time-concentration curve of the peritumoral brain edema was less prominent than that of the contralateral white matter, resulting in a significantly lower rrCBV (mean 46%) and rrCBF (mean 45%) in peritumoral brain edema than those of contralateral white matter. The serial perfusion-weighted MR imaging also demonstrated the recovery of these parameters after the removal of meningioma by means of surgical resection. Perfusion-weighted MR imaging can demonstrate significantly decreased rrCBV and rrCBF in peritumoral brain edema compared with those in normal white matter.

Functional MRI procedures in the diagnosis of brain tumors: Perfusion- and diffusion-weighted imaging

Despite the increased diagnostic accuracy of contrast material enhanced MR imaging, specification and grading of brain tumors are still only approximate at best: neither morphology, nor relaxation times or contrast material enhancement reliably predict tumor histology or tumor grade. As histology and tumor grade strongly influence which therapy concept is chosen, a more precise diagnosis is mandatory. With diffusion- and perfusion-weighted MR imaging (DWI, PWI) it is now possible to obtain important information regarding the cellular matrix and the relative regional cerebral blood volume (rrCBV) of brain tumors, which cannot be obtained with standard MR techniques. These dynamic-functional imaging techniques are very useful in the preoperative diagnosis of gliomas, lymphomas, and metastases, as well as in the differentiation of these neoplastic lesions from abscesses, atypical ischemic infarctions, and tumor-like manifestations of demyelinating disease. Additionally, they appear suitable for determining glioma grade and regions of active tumor growth which should be the target of stereotactic biopsy and therapy. After therapy these techniques are helpful to better assess the tumor response to therapy, possible therapy failure and therapy complications such as radiation necrosis.

Comparative evaluation of cerebral blood volume and cerebral blood flow in acute ischemic stroke by using perfusion-weighted MR imaging and SPECT.

To investigate the relationship between relative cerebral blood volume (CBV) measured with perfusion-weighted (PW) MR imaging and relative cerebral blood flow (CBF) measured with SPECT in acute ischemic stroke. Fifteen patients who had acute unilateral middle cerebral artery occlusion underwent both PW MR imaging and 99mTc-HMPAO SPECT with an interval less than 20 min between the two examinations within 6 h after stroke onset. Lesion-to-contralateral relative CBV and CBF ratios measured in multiple regions of interest were compared to evaluate the relationship of the two parameters. An overall linear relationship was found between relative CBV and relative CBF ratios (R2 = 0.54, p < 0.0001). The two parameters correlated linearly to each other in regions with evolving infarction (R2 = 0.43, p<0.0001), but not in regions without evolving infarction (R2 = 0.001, p>0.05). Regions with evolving infarction had more severe hypoperfusion (mean relative CBF ratio, 0.38 +/- 0.22) than regions without (mean relative CBF ratio, 0.70+/-0.13) (p<0.0001). A significant linear relationship existed between relative CBV and relative CBF in acute ischemic stroke, although relative CBV did not change linearly to relative CBF in mild hypoperfusion. Relative CBV can be used as an alternative to relative CBF within 6 h after stroke onset, particularly in regions with severe hypoperfusion proceeding to infarction.

Comparative evaluation of cerebral blood volume and cerebral blood flow in acute ischemic stroke by using perfusion-weighted MR imaging and spect

To investigate the relationship between relative cerebral blood volume (CBV) measured with perfusion-weighted (PW) MR imaging and relative cerebral blood flow (CBF) measured with SPECT in acute ischemic stroke. Fifteen patients who had acute unilateral middle cerebral artery occlusion underwent both PW MR imaging and 99mTc-HMPAO SPECT with an interval less than 20 min between the two examinations within 6 h after stroke onset. Lesion-to-contralateral relative CBV and CBF ratios measured in multiple regions of interest were compared to evaluate the relationship of the two parameters. An overall linear relationship was found between relative CBV and relative CBF ratios (R2 = 0.54, p < 0.0001). The two parameters correlated linearly to each other in regions with evolving infarction (R2 = 0.43, p<0.0001), but not in regions without evolving infarction (R2 = 0.001, p>0.05). Regions with evolving infarction had more severe hypoperfusion (mean relative CBF ratio, 0.38 +/- 0.22) than regions without (mean relative CBF ratio, 0.70+/-0.13) (p<0.0001). A significant linear relationship existed between relative CBV and relative CBF in acute ischemic stroke, although relative CBV did not change linearly to relative CBF in mild hypoperfusion. Relative CBV can be used as an alternative to relative CBF within 6 h after stroke onset, particularly in regions with severe hypoperfusion proceeding to infarction.

Neural substrates of the cognitive processes underlying spelling: Evidence from MR diffusion and perfusion imaging

Background: Despite a rich literature on the cognitive processes underlying spelling, there is little known about the neural substrates of these processes. Aims: The study aimed to identify regions of brain dysfunction associated with impairment of each cognitive process underlying spelling. It was hypothesised that impairments of distinct components of the spelling task would be associated with different areas of low blood flow or infarction in acute stroke patients. Methods & Procedures: Associations between impairment of each component of the spelling process and hypoperfusion and/or infarct of any of 11 Brodmann's areas (BAs) were identified in a consecutive series of 80 patients studied within 24 hours of onset of left hemisphere stroke. Impairment of each component of spelling was identified with tests of written naming, word comprehension, spelling words and pseudowords to dictation, direct and delayed copying, and case transcoding. Infarct and/or hypoperfusion in each BA was identified with MR diffusion-weighted imaging and perfusion-weighted imaging. Significant associations were identified with a correlation matrix, and the strongest associations were confirmed with chi square analysis. Outcomes & Results: Impairments of various cognitive processes were associated with separate regions of tissue dysfunction. Conclusions: It was concluded that spelling involves a network of relatively independent processes that rely on different brain regions.

High-grade gliomas and solitary metastases: differentiation by using perfusion and proton spectroscopic MR imaging.

To determine whether perfusion-weighted and proton spectroscopic MR imaging can be used to differentiate high-grade primary gliomas and solitary metastases on the basis of differences in vascularity and metabolite levels in the peritumoral region. Fifty-one patients with a solitary brain tumor (33 gliomas, 18 metastases) underwent conventional, contrast material--enhanced perfusion-weighted, and proton spectroscopic MR imaging before surgical resection or stereotactic biopsy. Of the 33 patients with gliomas, 22 underwent perfusion-weighted MR imaging; nine, spectroscopic MR imaging; and two underwent both. Of the 18 patients with metastases, 12 underwent perfusion-weighted MR imaging, and six, spectroscopic MR imaging. The peritumoral region was defined as the area in the white matter immediately adjacent to the enhancing (hyperintense on T2-weighted images, but not enhancing on postcontrast T1-weighted images) portion of the tumor. Relative cerebral blood volumes in these regions were calculated from perfusion-weighted MR data. Spectra from the enhancing tumor, the peritumoral region, and normal brain were obtained from the two-dimensional spectroscopic MR acquisition. The Student t test was used to determine if there was a statistically significant difference in relative cerebral blood volume and metabolic ratios between high-grade gliomas and metastases. The measured relative cerebral blood volumes in the peritumoral region in high-grade gliomas and metastases were 1.31 +/- 0.97 (mean +/- SD) and 0.39 +/- 0.19, respectively. The difference was statistically significant (P <.001). Spectroscopic imaging demonstrated elevated choline levels (choline-to-creatine ratio was 2.28 +/- 1.24) in the peritumoral region of gliomas but not in metastases (choline-to-creatine ratio was 0.76 +/- 0.23). The difference was statistically significant (P =.001). Although conventional MR imaging characteristics of solitary metastases and primary high-grade gliomas may sometimes be similar, perfusion-weighted and spectroscopic MR imaging enable distinction between the two.

A Case of MELAS: Hyperperfused Lesions Detected by Non-invasive Perfusion-weighted MR Imaging

We report a case of MELAS in which lesions were detected by perfusion-weighted MR imaging. Perfusion-weighted MRI using contrast media (PWI) and FAIR (flow-sensitive alternating inversion recovery), an arterial spin labeling method, clearly showed these lesions as hyperperfused areas. One of these lesions, diminished after steroid therapy, could also be detected by FAIR.

Tissue Viability Thresholds in Acute Stroke

Tissue Viability Thresholds in Acute Stroke

Late temporal lobe necrosis in patients with nasopharyngeal carcinoma: evaluation with combined multi-section diffusion weighted and perfusion weighted MR imaging

Late temporal lobe necrosis is a well-known and serious complication in patients with nasopharyngeal carcinoma (NPC) following radiotherapy. Owing to the close proximity to the skull base, the medial temporal lobes are inevitably included in the target volume of irradiation. Patients with NPC provide a unique opportunity in study of delay radiation effect in normal human brain. The objective of this study was to evaluate late temporal lobe radiation injury by combined multi-section diffusion weighted and perfusion weighted MR imaging. We prospectively studied 16 patients with typical clinical symptoms of late temporal lobe necrosis or other abnormalities in the temporal lobes incidentally detected by conventional MR imaging. All patients had a previous history of radiotherapy for histologically proven NPC. Conventional T1- and T2-weighted images, fast gradient echo with echo-planar diffusion-weighted and perfusion-weighted MR imaging were performed. Apparent diffusion coefficient (ADC) map and relative cerebral blood volume (rCBV) map were computed via commercially available software. MR diffusion and perfusion images were then analyzed and graded by two independent observers with focusing on the diffusion and perfusion mismatch. The temporal lobe lesions displayed marked high diffusion on the ADC map. The rCBV map also revealed marked hypoperfusion in these temporal lobe lesions in all patients. The areas of abnormality on the rCBV map were significantly larger than the lesions on the ADC map in 14 patients (observer 1) and 13 patients (observer 2). Since late temporal lobe necrosis is probably caused by damage of the endothelium of vessels and ischemia, perfusion and diffusion mismatch might imply injured tissue but potentially salvageable brain tissue. A mismatch may be potentially used to predict the response to treatment in-patients with late temporal lobe necrosis.