Xuexiang Jiang

Collateral Circulation Imaging: MR Perfusion Territory Arterial Spin-Labeling at 3T

BACKGROUND AND PURPOSE: Current knowledge of the collateral circulation remains sparse, and a noninvasive method to better characterize the role of collaterals is desirable. The aim of our study was to investigate the presence and distal flow of collaterals by using a new MR perfusion territory imaging, vessel-encoded arterial spin-labeling (VE-ASL). MATERIALS AND METHODS: Fifty-six patients with internal carotid artery (ICA) or middle cerebral artery (MCA) stenosis were identified by sonography. VE-ASL was performed to assess the presence and function of collateral flow. The perfusion information was combined with VE maps into high signal-intensity-to-noise-ratio 3-colored maps of the left carotid, right carotid, and posterior circulation territories. The presence of the anterior and posterior collateral flow was demonstrated by the color of the standard anterior cerebral artery/MCA flow territory. The distal function of collateral flow was categorized as adequate (cerebral blood flow [CBF] ≥10 mL/min/100 g) or deficient (CBF <10 mL/min/100 g). The results were compared with those of MR angiography (MRA) and intra-arterial digital subtraction angiography (DSA) in cross table, and κ coefficients were calculated to determine the agreement among different methods. RESULTS: The κ coefficients of the presence of anterior and posterior collaterals by using VE-ASL and MRA were 0.785 and 0.700, respectively. The κ coefficient of the function of collaterals by using VE-ASL and DSA was 0.726. Apart from collaterals through the circle of Willis, VE-ASL showed collateral flow via leptomeningeal anastomoses. CONCLUSIONS: In patients with ICA or MCA stenosis, VE-ASL could show the presence, the origin, and distal function of collateral flow noninvasively.

Quantitative cerebral blood flow mapping and functional connectivity of postherpetic neuralgia pain: A perfusion fMRI study

Summary This study investigated the postherpetic neuralgia pain‐related brain regions and the underlying seed‐based networks detected by arterial spin labeling. Abstract This article investigates the effects of postherpetic neuralgia (PHN) on resting‐state brain activity utilizing arterial spin labeling (ASL) techniques. Features of static and dynamic cerebral blood flow (CBF) were analyzed to reflect the specific brain response to PHN pain. Eleven consecutive patients suffering from PHN and 11 age‐ and gender‐matched control subjects underwent perfusion functional magnetic resonance imaging brain scanning during the resting state. Group comparison was conducted to detect the regions with significant changes of CBF in PHN patients. Then we chose those regions that were highly correlated with the self‐reported pain intensity as “seeds” to calculate the functional connectivity of both groups. Absolute CBF values of these regions were also compared across PHN patients and control subjects. Significant increases in CBF of the patient group were observed in left striatum, right thalamus, left primary somatosensory cortex (S1), left insula, left amygdala, left primary somatomotor cortex, and left inferior parietal lobule. Significant decreases in CBF were mainly located in the frontal cortex. Regional CBF in the left caudate, left insula, left S1, and right thalamus was highly correlated with the pain intensity, and further comparison showed that the regional CBF in these regions is significantly higher in PHN groups. Functional connectivity results demonstrated that the reward circuitry involved in striatum, prefrontal cortex, amygdala, and parahippocampal gyrus and the circuitry among striatum, thalamus, and insula were highly correlated with each element in PHN patients. In addition, noninvasive brain perfusion imaging at rest may provide novel insights into the central mechanisms underlying PHN pain.

The serial effect of iodinated contrast media on renal hemodynamics and oxygenation as evaluated by ASL and BOLD MRI.

Contrast-induced nephropathy is a prevalent cause of renal failure, and the mechanisms underlying this injury are not fully understood. We utilized noninvasive functional MRI in order to determine the serial effect of a single administration of iodinated contrast media (CM) on renal hemodynamics and oxygenation. Fifteen rabbits were randomized to receive an intravenous injection of CM (i.e. iopamidol-370; 6 ml kg(-1) body weight) or an equivalent amount of 0.9% saline. Both arterial spin-labeling and blood oxygen level-dependent imaging sequences were performed at 24 h before and at intervals of 1, 24, 48 and 72 h after injection to obtain serial renal blood flow (RBF) and relative spin-spin relaxation rate (R(2)*). Results showed that, in the iopamidol group, the mean cortical RBF decreased at 1 h (p = 0.04 vs baseline), reached its minimum at 24 h (p = 0.01) and gradually returned to baseline by 48 h (p = nonsignificant, NS). The outer medullary RBF decreased to its minimum by 24 h (p = 0.00) and remained less than baseline until 72 h. R(2)* in inner stripes was dramatically increased at 1 h (p = 0.00), remained elevated at 24 h (p = 0.05), but returned to baseline by 48 h (p = NS). R(2)* values within the cortex and outer stripes and inner medulla were slightly increased, but the changes did not reach a statistical significance (p = NS). Saline did not produce positive change in either RBF or R(2)* within different compartments of the kidney. We conclude that iopamidol is associated with a relatively longer-term hypoperfusion in whole kidney and decreased oxygen level in the inner stripes of the outer medulla.

Hemodynamic Effects of Furosemide on Renal Perfusion as Evaluated by ASL-MRI

RATIONALE AND OBJECTIVES The aim of this study was to investigate the short-term effects of furosemide on renal perfusion by using arterial spin labeling (ASL) magnetic resonance imaging. MATERIALS AND METHODS Eleven healthy human subjects were enrolled in the study. The measurement of renal blood flow (RBF) was performed by applying an ASL technique with flow-sensitive alternating inversion recovery spin preparation and a single-shot fast spin-echo imaging strategy on a 3.0-T magnetic resonance scanner. For all subjects, the ASL magnetic resonance images were obtained before agent injection as a baseline scan. Then 20 mg of furosemide was injected intravenously. Postfurosemide ASL images were acquired following administration to evaluate the renal hemodynamic response. RESULTS Postinjection scans showed that cortical RBF decreased from 366.59 ± 41.19 mL/100 g/min at baseline to 314.33 ± 48.83 mL/100 g/min at 10 minutes after the administration of furosemide (paired t test, P = .04 vs baseline), and medullary RBF decreased from 118.59 ± 24.69 mL/100 g/min at baseline to 97.38 ± 18.40 mL/100 g/min at 10 minutes after the administration of furosemide (paired t test, P = .01 vs baseline). There was a negative correlation between the furosemide-induced diuretic effect and the reduction of RBF (Spearmans r = -0.61). CONCLUSIONS The dominant hemodynamic effect of furosemide on the kidney is associated with a decrease in both cortical and medullary blood perfusion. Furthermore, the quantitative ASL technique may provide an alternative way to noninvasively monitor the change in renal function due to furosemide administration.

Effect of Iodinated Contrast Media on Renal Function Evaluated with Dynamic Three-dimensional MR Renography

PURPOSE To assess the hemodynamic effect of iodinated contrast media (CM) on glomerular filtration rate (GFR) by using dynamic three-dimensional magnetic resonance (MR) renography in a rabbit model. MATERIALS AND METHODS This study was approved by the university animal care and use committee. Twelve healthy male New Zealand rabbits (body mass range, 2.5-3.0 kg) were included. Two of them were sacrificed before MR examination to obtain renal histologic samples as controls. The other ten rabbits completed 4-minute dynamic contrast material-enhanced MR imaging 24 hours before and 20 minutes after intravenous injection of iopamidol (370 mg of iodine per milliliter) at a dose of 6 mL per kilogram of body weight. Blood volume (V(B)), GFR, and tubule volume (V(E)) of the renal cortex were determined with a two-compartment kinetic model. Maximum upslope (K(m)), peak concentration (P(c)), and initial 60-second area under the curve (IAUC) of the whole kidney renogram curve were measured with semiquantitative analysis. The self-control data were compared by using the Student paired t test. RESULTS Iopamidol significantly decreased cortical V(B) (mean, 42.53% ± 10.16 [standard deviation] before CM administration vs 27.23% ± 16.13 after CM administration; P < .01), V(E) (mean, 22.40% ± 11.69 before CM administration vs 11.51% ± 6.58 after CM administration; P < .01), and GFR (mean, 31.92 mL/100 g per minute ± 12.52 before CM administration vs 21.48 mL/100 g per minute ± 10.02 after CM administration; P < .01). Results of whole-kidney renogram analysis showed a decrease in K(m), P(c), and IAUC caused by iopamidol administration. CONCLUSION High-dose iopamidol resulted in a marked decrease in renal function, which could be detected at dynamic three-dimensional MR renography.

Low-contrast agent dose dual-energy CT monochromatic imaging in pulmonary angiography versus routine CT.

Objective This study aimed to retrospectively evaluate the feasibility and reliability of low-contrast agent dose dual-energy computed tomography (DECT) monochromatic imaging in pulmonary angiography. Methods Computed tomography pulmonary angiography was performed in 86 patients, 41 in 120-kVp computed tomography (CT) and 45 in DECT with low-contrast agent dose. The images in DECT were reconstructed at optimal kiloelectron-voltage (keV), demonstrating the best contrast-to-noise ratio between pulmonary artery and soft tissue, and at 70 keV. Image quality was compared by quantitative and subjective indexes. The radiation doses were recorded. Results Compared with 120-kVp CT, optimal keV showed superior quantitative indexes with inferior subjective image quality, whereas 70 keV demonstrated no statistical difference in quantitative indexes with superior subjective image quality. All suspicious pulmonary embolisms in DECT were diagnosed confidently by combination of 2 kinds of monochromatic imaging. The radiation dose in DECT is almost twice as 120-kVp CT. Conclusions Low-contrast agent dose DECT monochromatic imaging in pulmonary angiography accommodates superior intravascular enhancement and contrast in pulmonary arteries, and improves diagnostic confidence with compatible radiation dose.

Apparent Diffusion Coefficients of Metabolites in Patients with MELAS Using Diffusion-Weighted MR Spectroscopy

BACKGROUND AND PURPOSE: DW-MR spectroscopy can detect the diffusion coefficients of NAA, Cr, PCr, and Cho and can, therefore, provide some useful information. The aims of this study were to probe the mechanisms underlying the pathogenesis of MELAS and to see whether DW-MR spectroscopy is a useful technique for other diseases besides cerebral infarction. MATERIALS AND METHODS: Fifteen healthy volunteers and 10 patients with MELAS were enrolled in the study. All were scanned on a 3T whole-body MR imaging scanner. Fifteen ADCs of the singlet metabolites in the gray matter of the healthy subjects, 10 ADCs of the singlet metabolites in the lesions, and 8 ADCs of the singlet metabolites in the nonaffected areas were used in the statistical analysis, respectively. RESULTS: The metabolite ADCs of the nonaffected areas and the lesions in the patients were higher than those of the frontal gray matter in the healthy controls. There were significant differences between the metabolite ADCs of the nonaffected areas in patients and those in the healthy controls, and it was the same with the metabolite ADCs of the lesions and those of the healthy controls. CONCLUSIONS: The increased ADC values of the metabolites reveal that MELAS is a mitochondrial neuronopathy and involves the entire brain. DW-MR spectroscopy is a very useful noninvasive technique, which can show some valuable information that conventional MR imaging cannot display. Thus, it can be applied to brain diseases besides cerebral infarction.

Time course study on the effects of iodinated contrast medium on intrarenal water transport function using diffusion‐weighted MRI

To assess the effects of intravenous‐injected iodinated contrast medium (CM) on intrarenal water diffusion using noninvasive diffusion‐weighted MRI (DW‐MRI).

Blood oxygen level-dependent MRI for the monitoring of neoadjuvant chemotherapy in breast carcinoma: initial experience

PURPOSE To determine the feasibility of using R2* map MRI for pretreatment diagnosis and monitoring of tumor response to neoadjuvant chemotherapy (NAC) in patients with breast cancer. MATERIAL AND METHODS Twenty-eight women with breast cancer, as evidenced by pathology, underwent MR imaging prior to and after chemotherapy. All patients were examined by conventional MRI and R2* map imaging. Subjects were divided into major histological response (MHR) and non-major histological response (NMHR) groups. Mean R2* values of cancerous and normal glandular tissues were measured before and following NAC. Differences in R2* and ΔR2*% values between these two groups were compared with paired or independent t tests. The relationship between ΔR2*% and histological response was examined using Spearmans correlation test. RESULTS Before NAC, the average R2* values in carcinoma were lower than in normal glandular tissue (P<.05). After two to four cycles of NAC, the R2* values in carcinoma were increased (P<.05 ), but this change was not significant in normal glandular tissue. After NAC, ΔR2*% was significantly higher in MHR as compared to NMHR (P<.05). The ΔR2*% correlated with the histological response (r=0.581, P<.01). CONCLUSION In women undergoing NAC for breast cancer treatment, R2* and ΔR2*% appear to provide predictive information of tumor response which is probably associated with changes in tumor angiogenesis and tissue oxygenation. R2* map imaging of breasts may therefore be useful in monitoring tumor response to NAC.

Feasibility study of exploring a T1‐weighted dynamic contrast‐enhanced MR approach for brain perfusion imaging

To investigate the feasibility of T1‐weighted dynamic contrast‐enhanced (DCE) MRI for the measurement of brain perfusion.