Quantification of iron in the non-human primate brain with diffusion-weighted magnetic resonance imaging.

Pathological iron deposits in the brain, especially within basal ganglia, are linked to severe neurodegenerative disorders like Parkinson's disease. As iron induces local changes in magnetic susceptibility, its presence can be visualized with magnetic resonance imaging (MRI). The usual approach, based on iron induced changes in magnetic relaxation (T2/T2'), is often prone, however, to confounding artifacts and lacks specificity. Here, we propose a new method to quantify and map iron deposits using water diffusion MRI. This method is based on the differential sensitivity of two image acquisition schemes to the local magnetic field gradients induced by iron deposits and their cross-term with gradient pulses used for diffusion encoding. Iron concentration could be imaged and estimated with high accuracy in the brain cortex, the thalamus, the substantia nigra and the globus pallidus of macaques, showing iron distributions in agreement with literature. Additionally, iron maps could clearly show a dramatic increase in iron content upon injection of an UltraSmall Particle Iron Oxide (USPIO) contrast agent, notably in the cortex and the thalamus, reflecting regional differences in blood volume. The method will benefit clinical investigations on the effect of iron deposits in the brain or other organs, as iron deposits are increasingly seen as a biomarker for a wide range of diseases, notably, neurodegenerative diseases in the pre-symptomatic stage. It also has the potential for quantifying variations in blood volume induced by brain activation in fMRI studies using USPIOs.

Prediction of motor function outcome after intracerebral hemorrhage using fractional anisotropy calculated from diffusion tensor imaging.

BACKGROUND: The efficacy of surgical evacuation in patients with intracerebral hemorrhage (ICH) remains unclear for recovery of motor function. The relationship between improvement of motor function outcome and sequential change of fractional anisotropy (FA) values was investigated in patients with ICH, to explore whether motor function outcome can be predicted in the early phase. Indication of the surgical hematoma evacuation was also considered. METHODS: This prospective study included 23 patients with ICH. All patients underwent diffusion tensor imaging to measure the FA value five times: within 3 days, day 14, day 30, day 60, and day 90 after the onset. The regions of interest were determined on the b = 0 step of the echo planar imaging scans in the bilateral cerebral peduncles and were automatically transferred onto the FA images. The FA value was then calculated for each patient. Patients were divided into good and poor recovery groups according to the motor function outcome on day 90. RESULTS: The mean FA value of the poor recovery group gradually decreased until day 90, but remained unchanged in the good recovery group. The mean FA value on day 3 was significantly higher (p < 0.001) in the good recovery group (0.745 ± 0.0073) than in the poor recovery group (0.682 ± 0.0090). Receiver operating characteristic curve analysis showed that the FA value on day 3 could predict motor function outcome with a sensitivity of 100% and a specificity of 77.8% at an FA value of 0.7 on day 3. CONCLUSION: The main finding of this study was that the FA values of the cerebral peduncle on the pathological side in patients with ICH on day 3 could predict the motor function outcome on day 90.

Preoperative single-slab 3D time-of-flight magnetic resonance angiography predicts development of new cerebral ischemic events after carotid endarterectomy. Clinical article.

OBJECT: Preoperative impairment of cerebral hemodynamics predicts the development of new cerebral ischemic events after carotid endarterectomy (CEA), including neurological deficits and cerebral ischemic lesions on diffusion weighted MR imaging. Furthermore, the signal intensity of the middle cerebral artery (MCA) on single-slab 3D time-of-flight MR angiography (MRA) can assess hemodynamic impairment in the cerebral hemisphere. The purpose of the present study was to determine whether, on preoperative MR angiography, the signal intensity of the MCA can be used to identify patients at risk for development of cerebral ischemic events after CEA. METHODS: The signal intensity of the MCA ipsilateral to CEA on preoperative MR angiography was graded according to the ability to visualize the MCA in 106 patients with unilateral internal carotid artery stenosis (>or=70%). Diffusion weighted MR imaging was performed within 3 days of and 24 hours after surgery. The presence or absence of new postoperative neurological deficits was also evaluated. RESULTS: Cerebral ischemic events after CEA were observed in 16 patients. Reduced signal intensity of the MCA on preoperative MR angiography was the only significant independent predictor of postoperative cerebral ischemic events. When the reduced MCA signal intensity on preoperative MR angiography was defined as an impairment in cerebral hemodynamics, MR angiography grading resulted in an 88% sensitivity and 63% specificity, with a 30% positive- and a 97% negative-predictive value for the development of postoperative cerebral ischemic events. CONCLUSIONS: Signal intensity of the MCA on preoperative single-slab 3D time-of-flight MR angiography is useful for identifying patients at risk for cerebral ischemic events after CEA.

Preoperative prediction of cerebral hyperperfusion after carotid endarterectomy using middle cerebral artery signal intensity in 1.5-tesla magnetic resonance angiography followed by cerebrovascular reactivity to acetazolamide using brain perfusion single-photon emission computed tomography.

OBJECTIVE: The purpose of the present study was to determine whether the signal intensity of the middle cerebral artery (MCA) on preoperative 1.5-T magnetic resonance angiography (MRA) could identify patients at risk for hyperperfusion following carotid endarterectomy (CEA) as a clinical screening test and whether an additional measurement of preoperative cerebrovascular reactivity (CVR) to acetazolamide on brain perfusion single-photon emission computed tomography (SPECT) could increase the predictive accuracy for the development of hyperperfusion. METHODS: In 301 patients, the signal intensity of the MCA ipsilateral to CEA on MRA was preoperatively graded according to the ability to visualize the MCA. For patients with reduced MCA signal intensity on the MRA study, CVR to acetazolamide was subsequently assessed using brain perfusion SPECT. Cerebral hyperperfusion was determined intraoperatively using transcranial regional cerebral oxygen saturation monitoring with near-infrared spectroscopy. RESULTS: Preoperative reduced MCA signal intensity was significantly associated with the development of cerebral hyperperfusion (95% CI, 1.188-3.965; p = 0.0352). While the sensitivity and negative predictive value were 100% both for the preoperative MCA signal intensity alone and in combination with subsequent preoperative CVR to acetazolamide, the specificity and positive predictive value were significantly greater for the latter than for the former (p < 0.05). CONCLUSIONS: Signal intensity of the MCA on preoperative 1.5-T MRA identifies patients at risk for hyperperfusion following CEA as a clinical screening test. An additional measurement of preoperative CVR to acetazolamide increases the predictive accuracy for the development of hyperperfusion.

Effects of uncomplicated carotid endarterectomy on cognitive function and brain perfusion in patients with unilateral asymptomatic severe stenosis of the internal carotid artery by comparison with unoperated patients.

OBJECTIVE: The purpose of the present exploratory study was to evaluate the effects of uncomplicated carotid endarterectomy (CEA) on cognitive function and brain perfusion in patients with unilateral asymptomatic severe stenosis of the internal carotid artery (ICA) by comparison with unoperated patients. METHODS: Patients with age ≤75 years and unilateral asymptomatic severe stenosis (≥70%) of the cervical ICA underwent CEA with antiplatelet therapy (surgically treated group: 116 patients) or antiplatelet therapy alone or neither (medically treated group: 45 patients). For the surgically treated group, neuropsychological testing and brain perfusion measurement using single-photon emission computed tomography were performed within one month before surgery and one month after surgery. For the medically treated group, the same testing and measurement were performed twice at an interval of 1 to 2 months. RESULTS: None of the operated patients developed new major ischemic events after surgery or intraoperative cerebral hyperperfusion. None of the patients in the medically treated group experienced neurological deficits including transient ischemic attacks during the study period. The incidence of patients with interval cognitive improvement was significantly greater in the surgically treated group (11 patients: 9%) than in the medically treated group (0%) (p = 0.0352). The incidence of patients with interval brain perfusion improvement in the ipsilateral cerebral hemisphere was significantly greater in the surgically treated group (24 patients: 21%) than in the medically treated group (0%) (p = 0.0003). CONCLUSIONS: Uncomplicated CEA may improve cognitive function and brain perfusion in patients with unilateral asymptomatic severe stenosis of the ICA when compared with unoperated patients.

Does preoperative measurement of cerebral blood flow with acetazolamide challenge in addition to preoperative measurement of cerebral blood flow at the resting state increase the predictive accuracy of development of cerebral hyperperfusion after carotid endarterectomy? Results from 500 cases with brain perfusion single-photon emission computed tomography study.

The purpose of the present study was to determine whether preoperative measurement of cerebral blood flow (CBF) with acetazolamide in addition to preoperative measurement of CBF at the resting state increases the predictive accuracy of development of cerebral hyperperfusion after carotid endarterectomy (CEA). CBF at the resting state and cerebrovascular reactivity (CVR) to acetazolamide were quantitatively assessed using N-isopropyl-p-[(123)I]-iodoamphetamine (IMP)-autoradiography method with single-photon emission computed tomography (SPECT) before CEA in 500 patients with ipsilateral internal carotid artery stenosis (≥ 70%). CBF measurement using (123)I-IMP SPECT was also performed immediately and 3 days after CEA. A region of interest (ROI) was automatically placed in the middle cerebral artery territory in the affected cerebral hemisphere using a three-dimensional stereotactic ROI template. Preoperative decreases in CBF at the resting state [95% confidence intervals (CIs), 0.855 to 0.967; P = 0.0023] and preoperative decreases in CVR to acetazolamide (95% CIs, 0.844 to 0.912; P < 0.0001) were significant independent predictors of post-CEA hyperperfusion. The area under the receiver operating characteristic curve for prediction of the development of post-CEA hyperperfusion was significantly greater for CVR to acetazolamide than for CBF at the resting state (difference between areas, 0.173; P < 0.0001). Sensitivity, specificity, and positive- and negative-predictive values for the prediction of the development of post-CEA hyperperfusion were significantly greater for CVR to acetazolamide than for CBF at the resting state (P < 0.05, respectively). The present study demonstrated that preoperative measurement of CBF with acetazolamide in addition to preoperative measurement of CBF at the resting state increases the predictive accuracy of the development of post-CEA hyperperfusion.

Prediction of cerebral hyperperfusion after carotid endarterectomy using middle cerebral artery signal intensity in preoperative single-slab 3-dimensional time-of-flight magnetic resonance angiography.

OBJECTIVE: Cerebral hyperperfusion after carotid endarterectomy (CEA) occurs in patients with preoperative impairments in cerebral hemodynamics. Signal intensity of the middle cerebral artery (MCA) on single-slab 3-dimensional time-of-flight magnetic resonance angiography (MRA) can assess hemodynamic impairment in the cerebral hemisphere. The purpose of the present study was to determine whether the signal intensity of the MCA on preoperative MRA could identify patients at risk for cerebral hyperperfusion after CEA. METHODS: The signal intensity of the MCA ipsilateral to CEA on preoperative MRA was graded according to the ability to visualize the MCA in 81 patients with ipsilateral internal carotid artery stenosis (>or=70%). Cerebral blood flow was also quantified using single-photon emission computed tomography before and immediately after CEA and on the third postoperative day. RESULTS: Cerebral hyperperfusion immediately after CEA (cerebral blood flow increase >or=100% compared with preoperative values) was observed in 10 patients. Multivariate analysis revealed that only reduced signal intensity of the MCA was significantly associated with the development of postoperative cerebral hyperperfusion (95% confidence interval, 1.015-1.401; P = 0.0319). When the reduced signal intensity of the MCA on MRA was defined as an impairment in cerebral hemodynamics, MRA grading resulted in 100% sensitivity and 63% specificity, with a 28% positive predictive value and a 100% negative predictive value for the development of post-CEA hyperperfusion. Hyperperfusion syndrome developed on the fourth and sixth postoperative days in 2 of the 10 patients who exhibited hyperperfusion immediately after CEA. CONCLUSION: Signal intensity of the MCA, as assessed by this simple MRA method, may identify patients at risk for post-CEA cerebral hyperperfusion.