Diffusion‐weighted hyperpolarized 129Xe MRI in healthy volunteers and subjects with chronic obstructive pulmonary disease

Given its greater availability and lower cost, ¹²⁹Xe apparent diffusion coefficient (ADC) MRI offers an alternative to ³He ADC MRI. To demonstrate the feasibility of hyperpolarized ¹²⁹Xe ADC MRI, we present results from healthy volunteers (HV), chronic obstructive pulmonary disease (COPD) subjects, and age‐matched healthy controls (AMC). The mean parenchymal ADC was 0.036 ± 0.003 cm² sec^?1 for HV, 0.043 ± 0.006 cm² sec^?1 for AMC, and 0.056 ± 0.008 cm² sec^?1 for COPD subjects with emphysema. In healthy individuals, but not the COPD group, ADC decreased significantly in the anterior–posterior direction by ～22% (P = 0.006, AMC; 0.0059, HV), likely because of gravity‐induced tissue compression. The COPD group exhibited a significantly larger superior–inferior ADC reduction (～28%) than the healthy groups (～24%) (P = 0.00018, HV; P = 3.45 × 10^?5, AMC), consistent with smoking‐related tissue destruction in the superior lung. Superior–inferior gradients in healthy subjects may result from regional differences in xenon concentration. ADC was significantly correlated with pulmonary function tests (forced expiratory volume in 1 sec, r = ?0.77, P = 0.0002; forced expiratory volume in 1 sec/forced vital capacity, r = ?0.77, P = 0.0002; diffusing capacity of carbon monoxide in the lung/alveolar volume (V_A), r = ?0.77, P = 0.0002). In healthy groups, ADC increased with age by 0.0002 cm² sec^?1 year^?1 (r = 0.56, P = 0.02). This study shows that ¹²⁹Xe ADC MRI is clinically feasible, sufficiently sensitive to distinguish HV from subjects with emphysema, and detects age‐ and posture‐dependent changes. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Investigation of relationships between transverse relaxation rate,diffusion coefficient,and labeled cell concentration in ischemic rat brain using MRI

MRI has been used to evaluate labeled cell migration and distribution. However, quantitative determination of labeled cell concentration using MRI has not been systematically investigated. In the current study, we investigated the relationships between labeled cell concentration and MRI parameters of transverse relaxation rate, R₂, and apparent diffusion coefficient (ADC), in vitro in phantoms and in vivo in rats after stroke. Significant correlations were detected between iron concentration or labeled cell concentration and MRI measurements of R₂, ADC, and ADC×R₂ in vitro. In contrast, in vivo labeled cell concentration did not significantly correlate with R₂, ADC, and ADC×R₂. A major factor for the absence of a significant correlation between labeled cell concentration and MRI measurements in vivo may be attributed to background effects of ischemic tissue. By correcting the background effects caused by ischemic damage, ΔR₂ (difference in R₂ values in the ischemic tissue with and without labeled cells) exhibited a significant correlation to labeled cell concentration. Our study suggests that MRI parameters have the potential to quantitatively determine labeled cell concentration in vivo. Magn Reson Med, 2009. © 2008 Wiley‐Liss, Inc.     

Four‐dimensional transcatheter intraarterial perfusion (TRIP)‐MRI for monitoring liver tumor embolization in VX2 rabbits

Transcatheter intraarterial perfusion (TRIP)‐MRI is an intraprocedural technique to iteratively monitor liver tumor perfusion changes during transcatheter arterial embolization (TAE) and chemoembolization (TACE). However, previous TRIP‐MRI approaches using two‐dimensional (2D) T₁‐weighted saturation‐recovery gradient‐recalled echo (GRE) sequences provided only limited spatial coverage and limited capacity for accurate perfusion quantification. In this preclinical study, a quantitative 4D TRIP‐MRI technique (serial iterative 3D volumetric perfusion imaging) with rigorous radiofrequency (RF) B₁ field calibration and dynamic tissue longitudinal relaxation rate R₁ measurement is presented for monitoring intraprocedural liver tumor perfusion during TAE. 4D TRIP‐MRI and TAE were performed in five rabbits with eight VX2 liver tumors (N = 8). After B₁ calibrated baseline and dynamic R₁ quantification, subsequent tissue contrast agent concentration time curves were derived. A single‐input flow‐limited pharmacokinetic model and peak gradient method were applied for perfusion analysis. The perfusion Fρ reduced significantly from pre‐TAE 0.477 (95% confidence interval [CI]: 0.384–0.570) to post‐TAE 0.131 (95% CI: 0.080–0.183 ml/min/ml, P < 0.001). Magn Reson Med 60:970–975, 2008. © 2008 Wiley‐Liss, Inc.     

In vivo imaging of vessel diameter,size, and density: A comparative study between MRI and histology

The aim of this study was to compare magnetic resonance imaging (MRI) and histological estimates of the mean vessel diameter (mVD), the vessel density (Density), and the vessel size index (VSI) obtained in the same tumor‐bearing animals. Twenty‐seven rats bearing intracranial glioma (C6 or RG2) were imaged by MRI. Changes in transverse relaxations (ΔR and R₂) were induced by the injection of an iron‐based contrast agent and were mapped using a multi gradient‐echo spin‐echo sequence. Then, brain vascular network was studied ex vivo by histology. Three regions of interest were drawn in apparently normal tissue (neocortex and striatum) and in the tumor. In vivo mVD_MRI, Density_MRI, and VSI_MRI were measured; ex vivo, mVD_histo, Density_histo, and VSI_histo were quantified on the same animals. MRI and histology measurements differed by ?15 to 26%. A positive correlation was found between MRI and histology for mVD, Density, and VSI counterparts (R² = 0.62, 0.50, 0.73, respectively; P < 0.001 in all cases). This study indicates that MRI and histology yields well correlated the estimates of mVD, Density, and VSI. VSI is the closest MRI estimate to histology. As Density and mVD or VSI provide complementary information, it is worth computing them to characterize angiogenesis beyond blood volume fraction. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.     

Comparison of 1H blood oxygen level–dependent (BOLD) and 19F MRI to investigate tumor oxygenation

Fluorine‐19 [¹⁹F] MRI oximetry and ¹H blood oxygen level–dependent (BOLD) MRI were used to investigate tumor oxygenation in rat breast 13762NF carcinomas, and correlations between the techniques were examined. A range of tissue oxygen partial pressure (pO₂) values was found in the nine tumors while the anesthetized rats breathed air, with individual tumor pO₂ ranging from a mean of 1 to 36 torr and hypoxic fraction (HF10) (<10 torr) ranging from 0% to 75%, indicating a large intra‐ and intertumor heterogeneity. Breathing oxygen produced significant increase in tumor pO₂ (mean ΔpO₂ = 50 torr) and decrease in HF₁₀ (P < 0.01). ¹H BOLD MRI observed using a spin echo‐planar imaging (EPI) sequence revealed a heterogeneous response and significant increase in mean tumor signal intensity (SI) (ΔSI = 7%, P < 0.01). R measured by multigradient‐echo (MGRE) MRI decreased significantly in response to oxygen (mean ΔR = ?4 s^?1; P < 0.05). A significant correlation was found between changes in mean tumor pO₂ and mean EPI BOLD ΔSI accompanying oxygen breathing (r² > 0.7, P < 0.001). Our results suggest that BOLD MRI provides information about tumor oxygenation and may be useful to predict pO₂ changes accompanying interventions. Significantly, the magnitude of the BOLD response appears to be predictive for residual tumor HFs. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Compensation of slice profile mismatch in combined spin‐ and gradient‐echo echo‐planar imaging pulse sequences

Combined acquisition of gradient‐echo and spin‐echo signals in MRI time series reveals additional information for perfusion‐weighted imaging and functional MRI because of differences in the sensitivity of gradient‐echo and spin‐echo measurements to the properties of the underlying vascular architecture. The acquisition of multiple echo trains within one time frame facilitates the simultaneous estimation of the transversal relaxation parameters R₂ and R. However, the simultaneous estimation of these parameters tends to be incorrect in the presence of slice profile mismatches between signal excitation and subsequent refocusing pulses. It is shown here that improvements in pulse design reduced R₂ and R estimation errors. Further improvements were achieved by augmented parameter estimation through the introduction of an additional parameter δ to correct for discordances in slice profiles to facilitate more quantitative measurements. Moreover, the analysis of time‐resolved acquisitions revealed that the temporal stability of R₂ estimates could be increased with improved pulse design, counteracting low contrast‐to‐noise ratios in spin‐echo‐based perfusion and functional MRI. Magn Reson Med, 2012. © 2011 Wiley Periodicals, Inc.     

Evaluation of hepatic fibrosis with portal pressure gradient in rats

MRI has the potential of providing a noninvasive assessment of liver pathology. This work introduces a portal pressure gradient (PPG) model derived from fluid mechanics, where the PPG is proportional to the average velocity and inversely proportional to the vessel area in the upper part of portal vein. Using a phase‐contrast spoiled gradient echo sequence, the PPG model was verified in a phantom study and was tested in an animal study using 35 rats with various degrees of hepatic fibrosis induced by carbon tetrachloride (CCl₄). Histological examination was conducted to determine the severity of hepatic fibrosis. The fibrosis score monotonically increased with the duration of CCl₄ treatment. The PPG was highly correlated with nonzero fibrosis scores (r² = 0.90, P < 0.05). There was a significant difference between control and cirrhosis groups (P < 0.0006, α < 0.0018). The difference between control and fibrosis (noncirrhosis) groups (P < 0.002, α < 0.006) was also significant. Without the administration of any contrast agent, the MRI‐PPG approach shows promise as a noninvasive means of evaluating liver fibrosis. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Diffusion-weighted and dynamic contrast-enhanced MRI in evaluation of early treatment effects during neoadjuvant chemotherapy in breast cancer patients

Purpose:

To use dynamic contrast‐enhanced (DCE) and diffusion‐weighted (DW) MRI at 3 Tesla (T) for early evaluation of treatment effects in breast cancer patients undergoing neoadjuvant chemotherapy (NAC), and assess the reliability of DW‐MRI.

Materials and Methods:

DW‐ and DCE‐MRI acquisitions of 15 breast cancer patients were performed before and after one cycle of NAC. MRI tumor diameter and volume, apparent diffusion coefficient (ADC) and kinetic parameters (K^trans, v_e) were derived. The reliability of ADC before NAC was assessed. Changes in MRI parameters after NAC were analyzed, and logistic regression analysis was used to find the best predictors for pathologic response.

Results:

The reliability for ADC values was high, with intraclass correlation coefficient of 0.84 (P = 0.001). After one cycle of NAC, MRI tumor diameter (8%, P = 0.005) and tumor volume (30%, P = 0.008) was reduced for all patients, while ADC mean values increased (0.12 mm²/s, P = 0.008). The best predictor for treatment response was a change in MRI tumor diameter with mean error rate of 0.167 (13% for responders, 5% for nonresponders, P = 0.291).

Conclusion:

Changes in MRI derived tumor diameter and ADC after only one cycle of NAC could provide a valuable tool for early evaluation of treatment effects in breast cancer patients. J. Magn. Reson. Imaging 2011;. © 2011 Wiley Periodicals, Inc.     

Effect of disease progression on liver apparent diffusion coefficient and T2 values in a murine model of hepatic fibrosis at 11.7 Tesla MRI

Purpose:

To evaluate the effects of hepatic fibrosis on ADC and T₂ values of ex vivo murine liver specimens imaged using 11.7 Tesla (T) MRI.

Materials and Methods:

This animal study was IACUC approved. Seventeen male, C57BL/6 mice were divided into control (n = 2) and experimental groups (n = 15), the latter fed a 3, 5‐dicarbethoxy‐1, 4‐dihydrocollidine (DDC) supplemented diet, inducing hepatic fibrosis. Ex vivo liver specimens were imaged using an 11.7T MRI scanner. Spin‐echo pulsed field gradient and multi‐echo spin‐echo acquisitions were used to generate parametric ADC and T₂ maps, respectively. Degrees of fibrosis were determined by the evaluation of a pathologist as well as digital image analysis. Scatterplot graphs comparing ADC and T₂ to degrees of fibrosis were generated and correlation coefficients were calculated.

Results:

Strong correlation was found between degrees of hepatic fibrosis and ADC with higher degrees of fibrosis associated with lower hepatic ADC values. Moderate correlation between hepatic fibrosis and T₂ values was seen with higher degrees of fibrosis associated with lower T₂ values.

Conclusion:

Inverse relationships between degrees of fibrosis and both ADC and T₂ are seen, highlighting the utility of these parameters in the ongoing development of an MRI methodology to quantify hepatic fibrosis. J. Magn. Reson. Imaging 2012;35:140‐146. © 2011 Wiley Periodicals, Inc.     

2D and 3D radial multi‐gradient‐echo DCE MRI in murine tumor models with dynamic R*2‐corrected R1 mapping

Dynamic contrast‐enhanced MRI is extensively studied to define and evaluate biomarkers for early assessment of vasculature‐targeting therapies. In this study, two‐dimensional and three‐dimensional radial multi‐gradient‐echo techniques for dynamic R*₂‐corrected R₁ mapping based on the spoiled gradient recalled signal equation were implemented and validated at 4.7 T. The techniques were evaluated on phantoms and on a respiratory motion animated tumor model. R₁ measurements were validated with respect to a standard inversion‐recovery spin‐echo sequence in a four‐compartment phantom covering a range of relaxation rates typically found in tumor tissue. In the range of [0.4, 3] sec^?1, R₁ differences were less than 10% for both two‐dimensional and three‐dimensional experiments. A dynamic contrast‐enhanced MRI pilot study was performed on a colorectal tumor model subcutaneously implanted in mice at the abdominal level. Low motion sensitivity of radial acquisition allowed image recording without respiratory triggering. Three‐dimensional K^trans maps and significantly different mean K^trans values were obtained for two contrast agents with different molecular weights. The radial multi‐gradient‐echo approach should be most useful for preclinical experimental conditions where the tissue of interest experiences physiologic motion, like spontaneous extracerebral tumors developed by transgenic mice, and where dynamic contrast‐enhanced MRI is performed with high‐relaxivity contrast agents. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

An improved method for acquiring cerebrovascular reactivity maps

This study aims to improve the method used to produce cerebrovascular reactivity (CVR) maps by MRI. Previous methods have used a standard boxcar presentation of carbon dioxide (CO₂). Here this is replaced with a sinusoidally modulated CO₂ stimulus. This allowed the use of Fourier analysis techniques to measure both the amplitude and phase delay of the BOLD CVR response, and hence characterize the arrival sequence of blood to different regions of the brain. This characterization revealed statistically significant relative delays between regions of the brain (ANOVA < 0.0001). In addition, post hoc comparison showed that the frontal (P < 0.001) and parietal (P = 0.004) lobes reacted earlier than the occipital lobe. Magn Reson Med, 2011. © 2010 Wiley‐Liss, Inc.     

Quantification of venous vessel size in human brain in response to hypercapnia and hyperoxia using magnetic resonance imaging

Hypercapnia and hyperoxia give rise to vasodilation and vasoconstriction, respectively. This study investigates the influence of hypercapnia and hyperoxia on venous vessel size in the human brain. Venous vessel radii were measured in response to hypercapnia and hyperoxia. The venous vessel radii were determined by calculation of the changes in R₂* and R₂ that are induced by breathing 6% CO₂ or pure oxygen. The experimental paradigm consisted of two 3‐min intervals of inhaling 6% CO₂ or 100% O₂ interleaved with three 2‐min intervals of breathing air. Hypercapnic and hyperoxic experiments were performed on eight subjects on a 3T scanner. Parametric maps of mean venous vessel radius were calculated from the changes in R₂* and R₂, which were measured by simultaneous acquisition of gradient‐echo and spin‐echo signals. The mean venous vessel radii in hypercapnia were 7.3 ± 0.3 μm in gray matter and 6.6 ± 0.5 μm in white matter. The corresponding vessel radii in hyperoxia were 5.6 ± 0.2 μm in gray matter and 5.4 ± 0.2 μm in white matter. These results show that the venous vessel radius was larger in hypercapnia than that in hyperoxia in both gray matter and white matter (P < 0.005), which agrees with the hypothesis that hypercapnia causes vasodilation and hyperoxia induces vasoconstriction. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.     

Hepatic fat quantification using chemical shift MR imaging and MR spectroscopy in the presence of hepatic iron deposition: validation in phantoms and in patients with chronic liver disease

Purpose:

To compare the accuracy of four chemical shift magnetic resonance imaging (MRI) (CS‐MRI) analysis methods and MR spectroscopy (MRS) with and without T2‐correction in fat quantification in the presence of excess iron.

Materials and Methods:

CS‐MRI with six opposed‐ and in‐phase acquisitions and MRS with five‐echo acquisitions (TEs of 20, 30, 40, 50, 60 msec) were performed at 1.5 T on phantoms containing various fat fractions (FFs), on phantoms containing various iron concentrations, and in 18 patients with chronic liver disease. For CS‐MRI, FFs were estimated with the dual‐echo method, with two T2*‐correction methods (triple‐ and multiecho), and with multiinterference methods that corrected for both T2* and spectral interference effects. For MRS, FF was estimated without T2‐correction (single‐echo MRS) and with T2‐correction (multiecho MRS).

Results:

In the phantoms, T2*‐ or T2‐correction methods for CS‐MRI and MRS provided unbiased estimations of FFs (mean bias, ?1.1% to 0.5%) regardless of iron concentration, whereas the dual‐echo method (?5.5% to ?8.4%) and single‐echo MRS (12.1% to 37.3%) resulted in large biases in FFs. In patients, the FFs estimated with triple‐echo (R = 0.98), multiecho (R = 0.99), and multiinterference (R = 0.99) methods had stronger correlations with multiecho MRS FFs than with the dual‐echo method (R = 0.86; P ≤ 0.011). The FFs estimated with multiinterference method showed the closest agreement with multiecho MRS FFs (the 95% limit‐of‐agreement, ?0.2 ± 1.1).

Conclusion:

T2*‐ or T2‐correction methods are effective in correcting the confounding effects of iron, enabling an accurate fat quantification throughout a wide range of iron concentrations. Spectral modeling of fat may further improve the accuracy of CS‐MRI in fat quantification. J. Magn. Reson. Imaging 2011;33:1390–1398. © 2011 Wiley‐Liss, Inc.

     

Changes in apparent diffusion coefficient and T2 relaxation during radiotherapy for prostate cancer

Purpose:

To evaluate regional and temporal changes in apparent diffusion coefficient (ADC) and T₂ relaxation during radiation therapy (RT) in patients with low and intermediate risk localized prostate cancer.

Materials and Methods:

Seventeen patients enrolled on a prospective clinical trial where MRI was acquired every 2 weeks throughout eight weeks of image‐guided prostate IMRT (78 Gy/39 fractions). ADC and T₂ quantification used entire prostate, central gland, benign peripheral zone, and tumor‐dense regions‐of‐interest, and mean values were evaluated for common response trends.

Results:

Overall, the RT responses were greater than volunteer measurement repeatability, and week 6 appeared to be an optimum time‐point for early detection. RT effects on the entire prostate were best detected using ADC (5–7% by week 2, P < 0.0125), effects on peripheral zone were best detected using T₂ (19% reduction at week 6; P = 0.004) and effects on tumors were best detected using ADC (14% elevation at week 6; P = 0.004).

Conclusion:

ADC and T₂ may be candidate biomarkers of early response to RT warranting further investigation against clinical outcomes. J. Magn. Reson. Imaging 2013;37:909–916. © 2012 Wiley Periodicals, Inc.     

Breathhold multiecho fast spin‐echo pulse sequence for accurate R2 measurement in the heart and liver

Measurement of proton transverse relaxation rates (R₂) is a generally useful means for quantitative characterization of pathological changes in tissue with a variety of clinical applications. The most widely used R₂ measurement method is the Carr‐Purcell‐Meiboom‐Gill (CPMG) pulse sequence but its relatively long scan time requires respiratory gating for chest or body MRI, rendering this approach impractical for comprehensive assessment within a clinically‐acceptable examination time. The purpose of our study was to develop a breathhold multiecho fast spin‐echo (FSE) sequence for accurate measurement of R₂ in the liver and heart. Phantom experiments and studies of subjects in vivo were performed to compare the FSE data with the corresponding even‐echo CPMG data. For pooled data, the R₂ measurements were strongly correlated (Pearson correlation coefficient = 0.99) and in excellent agreement (mean difference [CPMG – FSE] = 0.10 s^–1; 95% limits of agreement were 1.98 and –1.78 s^–1) between the two pulse sequences. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.     

Respiratory self‐gated multiple gradient recalled echo sequence for free‐breathing abdominal R2* mapping

Abdominal effective transverse relaxation rate (R₂*) mapping is critical for a wide range of applications. However, respiratory motion can lead to significant image quality deterioration and R₂* overestimation. For this work, we explored the feasibility of combining respiratory self‐gating techniques with a multiple gradient‐recalled echo sequence for free‐breathing abdominal R₂* measurements. In a series of eight normal volunteers, respiratory self‐gated–multiple gradient‐recalled echo methods effectively avoided motion artifacts to produce quantitative R₂* measurements in liver, spleen, and kidneys that were comparable to R₂* measurements produced while breath‐holding. Respiratory self‐gated–multiple gradient‐recalled echo methods demonstrated the potential to avoid the need for breath‐holding during abdominal R₂* mapping. For clinical application, respiratory self‐gated–multiple gradient‐recalled echo approaches could be particularly useful for R₂* measurements in those patients unable or unwilling to sustain sufficiently long breath‐holds to avoid motion artifacts. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

Dynamic hysteresis between gradient echo and spin echo attenuations in dynamic susceptibility contrast imaging

Perfusion measurements using dynamic susceptibility contrast imaging provide additional information about the mean vessel size of microvasculature when supplemented with a dual gradient echo (GE) – spin echo (SE) contrast. Dynamic increase in the corresponding transverse relaxation rate constant changes, ΔR_2GE and ΔR_2SE, forms a loop on the (Δ, ΔR_2GE) plane, rather than a reversible line. The shape of the loop and the direction of its passage differentiate between healthy brain and pathological tissue, such as tumour and ischemic tissue. By considering a tree model of microvasculature, the direction of the loop is found to be influenced mainly by the relative arterial and venous blood volume, as well as the tracer bolus dispersion. A parameter Λ is proposed to characterize the direction and shape of the loop, which might be considered as a novel imaging marker for describing the pathology of cerebrovascular network. Magn Reson Med 69:981–991, 2013. © 2012 Wiley Periodicals, Inc.     

Acetazolamide-challenged perfusion magnetic resonance imaging for assessment of cerebrovascular reserve capacity in patients with symptomatic middle cerebral artery stenosis: comparison with technetium-99m-hexamethylpropyleneamine oxime single-photon emission computed tomography

Objectives

Acetazolamide-challenged perfusion magnetic resonance imaging (MRI) has been shown as a method for assessment of cerebrovascular reserve (CVR) capacity in patients with atherosclerotic steno-occlusive disease of internal carotid artery. We have assessed the feasibility of the acetazolamide-challenged perfusion MRI for evaluating CVR in symptomatic patients with severe middle cerebral artery (MCA) stenosis (≥70%) by comparison with the acetazolamide-challenged technetium-99m-hexamethylpropyleneamine oxime (HMPAO) single-photon emission computed tomography (SPECT).

Methods

Seventeen prospectively enrolled patients with symptomatic unilateral MCA stenosis underwent technetium-99m-hexamethylpropyleneamine oxime SPECT and perfusion MRI without and with acetazolamide challenge, respectively. Acetazolamide-challenged SPECT and perfusion MRI were compared quantitatively by Region of interest (ROI) analysis.

Results

At all ROIs, there were no significant differences in percent change between SPECT and perfusion MRI. Patients with impaired CVR showed significant decreases in the percent changes of respective cerebral blood flow (P=.016) and respective cerebral blood volume (P=.029).

Conclusion

Acetazolamide-challenged perfusion MRI is feasible for evaluating CVR in symptomatic patients with severe MCA stenosis quantitatively.     

Correlative assessment of cerebral blood flow obtained with perfusion CT and positron emission tomography in symptomatic stenotic carotid disease

Twelve patients with ICA stenosis underwent dynamic perfusion computed tomography (CT) and positron emission tomography (PET) studies at rest and after acetazolamide challenge. Cerebral blood flow (CBF) maps on perfusion CT resulted from a deconvolution of parenchymal time-concentration curves by an arterial input function (AIF) in the anterior cerebral artery as well as in both anterior choroidal arteries. CBF was measured by [¹⁵O]H₂O PET using multilinear least-squares minimization procedure based on the one-compartment model. In corresponding transaxial PET scans, CBF values were extracted using standardized ROIs. The baseline perfusion CT-CBF values were lower in perfusion CT than in PET (P>0.05). CBF values obtained by perfusion CT were significantly correlated with those measured by PET before (P<0.05) and after (P<0.01) acetazolamide challenge. Nevertheless, the cerebrovascular reserve capacity was overestimated (P=0.05) using perfusion CT measurements. The AIF selection relative to the side of carotid stenosis did not significantly affect calculated perfusion CT-CBF values. In conclusion, the perfusion CT-CBF measurements correlate significantly with the PET-CBF measurements in chronic carotid stenotic disease and contribute useful information to the evaluation of the altered cerebral hemodynamics.     

Multicompartmental analysis of late contrast enhancement in areas of myocardial infarction supplied by chronically occluded coronary arteries

Purpose

To analyze the relationship between late contrast enhancement (LCE) and the interstitial distribution volume (V_In) of gadolinium (Gd) tracers in the myocardial infarction (MI) areas supplied by chronically occluded arteries from patients. In animal experimental models, LCE has already been shown to correspond to an enhanced V_In of Gd tracers and thus, to a decrease in the amount of intact cells.

Materials and Methods

A multicompartmental analysis was applied to serial MRI images encompassing both infarct and remote areas and recorded with a conventional two‐dimensional (2D) segmented inversion‐recovery gradient‐echo (IR‐GRE) sequence during a 15‐minute period following Gd‐diethylenetriamine pentaacetic acid (Gd‐DTPA) injection in 12 patients with Q‐wave MI supplied by chronically occluded coronary arteries.

Results

V_In from infarct tissue was: 1) higher than V_In from remote areas (in % of myocardial volume: 74 ± 16% vs. 20 ± 7%, P < 0.001); and 2) correlated with the quantification of LCE between infarct and noninfarct areas at the 15th minute (R² = 0.63, P = 0.002). However, the difference in V_In between infarct and remote myocardium was a much better correlate of this quantified LCE (R² = 0.85, P < 0.001).

Conclusion

Detection of LCE in the MI territories supplied by chronically occluded arteries relates to the difference in the V_In of tracers between the infarct and the noninfarct areas. J. Magn. Reson. Imaging 2009;29:78–85. © 2008 Wiley‐Liss, Inc.