Improved visualization of the human lung in 1H MRI using multiple inversion recovery for simultaneous suppression of signal contributions from fat and muscle

1H magnetic resonance imaging of the lung is hampered by the low contrast between lung parenchyma, and muscle and fat in the thorax. We show that it is possible to improve contrast greatly and thereby enhance the visibility of the lung, by suppression of signal of surrounding muscle and fat based on differences in T1 relaxation times using a double inversion recovery preparation pulses (TI1 800 msec, and TI2 150 msec) and a half-Fourier acquisition single-shot turbo spin-echo (HASTE) sequence. The measured T1 values for the right and left lungs at 1.5 T were 1.37 +/- 0.18 and 1.41 +/- 0.21 sec, respectively.

A novel voluntary weightlifting model in mice promotes muscle adaptation and insulin sensitivity with simultaneous enhancement of autophagy and mTOR pathway

Our understanding of the molecular mechanisms underlying adaptations to resistance exercise remains elusive despite the significant biological and clinical relevance. We developed a novel voluntary mouse weightlifting model, which elicits squat-like activities against adjustable load during feeding, to investigate the resistance exercise-induced contractile and metabolic adaptations. RNAseq analysis revealed that a single bout of weightlifting induced significant transcriptome responses of genes that function in posttranslational modification, metabolism, and muscle differentiation in recruited skeletal muscles, which were confirmed by increased expression of fibroblast growth factor-inducible 14 (Fn14), Down syndrome critical region 1 (Dscr1) and Nuclear receptor subfamily 4, group A, member 3 (Nr4a3) genes. Long-term (8 weeks) voluntary weightlifting training resulted in significantly increases of muscle mass, protein synthesis (puromycin incorporation in SUnSET assay) and mTOR pathway protein expression (raptor, 4e-bp-1, and p70S6K proteins) along with enhanced muscle power (specific torque and contraction speed), but not endurance capacity, mitochondrial biogenesis, and fiber type transformation. Importantly, weightlifting training profound improved whole-body glucose clearance and skeletal muscle insulin sensitivity along with enhanced autophagy (increased LC3 and LC3-II/I ratio, and decreased p62/Sqstm1). These data suggest that resistance training in mice promotes muscle adaptation and insulin sensitivity with simultaneous enhancement of autophagy and mTOR pathway.

Nitric Oxide Mediates Benefits of Angiotensin II Type 2 Receptor Overexpression During Post-Infarct Remodeling

We hypothesized that nitric oxide (NO) mediates the benefits of cardiac angiotensin II type 2 (AT(2)-R) overexpression during postmyocardial infarction (post-MI) remodeling. Eleven wild-type (WT) C57BL/6 mice and 28 transgenic (TG) mice with AT(2)-R overexpression were studied by cardiac magnetic resonance imaging (CMR) at baseline and days 1 and 28 post-MI induced by left anterior descending artery occlusion and reperfusion. Sixteen TG mice were treated from day 1 through 28 post-MI with the NO synthase inhibitor N(G)-nitro-l-arginine methyl ester in drinking water at 1 mg/mL (TG-Rx). Left ventricular mass index (LVMI), end-diastolic volume index (EDVI) and end-systolic volume index (ESVI), wall thickness, percent thickening, and ejection fraction (EF) were measured. Infarct size on day 1 was assessed by post-contrast CMR. Interstitial collagen was quantified in noninfarcted regions. At baseline, heart rate (HR), blood pressure (BP), LVMI, EDVI, and ESVI were similar between groups, as were infarct size and weekly post-MI HR and systolic BP. By day 28 post-MI, EDVI and ESVI were similar in WT and TG-Rx, but significantly lower in TG (ESVI: 1.41+/-0.18 microL/g versus 2.53+/-0.14 microL/g in WT; 2.17+/-0.14 microL/g in TG-Rx; P<0.008 for both). At day 28, EF was higher in TG (46.3%+/-2.9%) compared with WT and TG-Rx (32.7+/-2.3% and 33.7+/-2.3, respectively; P<0.003 for both). Wall thickening at day 28 post-MI was greater in the base and mid-LV in TG than WT and TG-Rx. Noninfarcted region interstitial collagen was similar between groups. Thus, the NO pathway may mediate much of the benefits of cardiac AT(2)-R overexpression during post-MI remodeling.

T₂ -weighted MRI of post-infarct myocardial edema in mice

T(2) -weighted, cardiac magnetic resonance imaging (T(2) w CMR) can be used to noninvasively detect and quantify the edematous region that corresponds to the area at risk (AAR) following myocardial infarction (MI). Previously, CMR has been used to examine structure and function in mice, expediting the study of genetic manipulations. To date, CMR has not been applied to imaging of post-MI AAR in mice. We developed a whole-heart, T(2) w CMR sequence to quantify the AAR in mouse models of ischemia and infarction. The ΔB(0) and ΔB(1) environment around the mouse heart at 7 T were measured, and a T(2) -preparation sequence suitable for these conditions was developed. Both in vivo T(2) w and late gadolinium enhanced CMR were performed in mice after 20-min coronary occlusions, resulting in measurements of AAR size of 32.5 ± 3.1 (mean ± SEM)% left ventricular mass, and MI size of 50.1 ± 6.4% AAR size. Excellent interobserver agreement and agreement with histology were also found. This T(2) w imaging method for mice may allow for future investigations of genetic manipulations and novel therapies affecting the AAR and salvaged myocardium following reperfused MI.

In vitro evaluation of endothelial exosomes as carriers for small interfering ribonucleic acid delivery

Exosomes, one subpopulation of nanosize extracellular vesicles derived from multivesicular bodies, ranging from 30 to 150 nm in size, emerged as promising carriers for small interfering ribonucleic acid (siRNA) delivery, as they are capable of transmitting molecular messages between cells through carried small noncoding RNAs, messenger RNAs, deoxyribonucleic acids, and proteins. Endothelial cells are involved in a number of important biological processes, and are a major source of circulating exosomes. In this study, we prepared exosomes from endothelial cells and evaluated their capacity to deliver siRNA into primary endothelial cells. Exosomes were isolated and purified by sequential centrifugation and ultracentrifugation from cultured mouse aortic endothelial cells. Similar to exosome particles from other cell sources, endothelial exosomes are nanometer-size vesicles, examined by both the NanoSight instrument and transmission electron microscopy. Enzyme-linked immunosorbent assay analysis confirmed the expression of two exosome markers: CD9 and CD63. Flow cytometry and fluorescence microscopy studies demonstrated that endothelial exosomes were heterogeneously distributed within cells. In a gene-silencing study with luciferase-expressing endothelial cells, exosomes loaded with siRNA inhibited luciferase expression by more than 40%. In contrast, siRNA alone and control siRNA only suppressed luciferase expression by less than 15%. In conclusion, we demonstrated that endothelial exosomes have the capability to accommodate and deliver short foreign nucleic acids into endothelial cells.

Transgenic A1 adenosine receptor overexpression markedly improves myocardial energy state during ischemia-reperfusion

A1 adenosine (A1AR) activation may reduce ischemia-reperfusion injury. Metabolic and functional responses to 30 min global normothermic ischemia and 20 min reperfusion were compared in wild-type and transgenic mouse hearts with approximately 100-fold overexpression of coupled cardiac A1ARs. 31P-NMR spectroscopy revealed that ATP was better preserved in transgenic v wild-type hearts: 53 +/- 11% of preischemic ATP remained after ischemia in transgenic hearts v only 4 +/- 4% in wild-type hearts. However, recovery of ATP after reperfusion was similar in transgenic (46 +/- 5%) and wild-type hearts (37 +/- 12%). Reductions in phosphocreatine (PCr) and cytosolic pH during ischemia were similar in both groups. However, recovery of PCR on reperfusion was higher in transgenic (67 +/- 8%) v wild-type hearts (36 +/- 8%), and recovery of pH was greater in transgenic (pH = 7.11 +/- 0.05) v wild-type hearts (pH = 6.90 +/- 0.02). Bioenergetic state ([ATP]/[ADP].[Pi]) was higher in transgenic v wild-type hearts during ischemia-reperfusion. Time to ischemic contracture was prolonged in transgenic (13.6 +/- 0.8 min) v wild-type hearts (10.4 +/- 0.3 min). Degree of contracture was lower and recovery of function in reperfusion higher in transgenic v wild-type hearts. In conclusion, A1AR overexpression reduces ATP loss and improves bioenergetic state during severe ischemic insult and reperfusion. These changes may contribute to improved functional tolerance.

Reperfused myocardial infarction in mice: 3D mapping of late gadolinium enhancement and strain

We developed mathematical modeling tools for mapping 3D infarct geometry from multislice late gadolinium enhancement data, allowing fusion with multislice MR tagging data, in mice with myocardial infarction. Five C57BL/6 mice were imaged at baseline, 1, 7 and 28 days after 60 min occlusion of the left anterior descending coronary artery. The 3D infarct geometry was mapped in material coordinates, and registered with 3D strain, showing permanent dysfunction in infarcted segments, intermediate function in the adjacent zone, and maintained function in the remote zone. 3D mapping of late enhancement and strain allows registration of multiple studies in a consistent framework.

ImmunoPET-informed sequence for focused ultrasound-targeted mCD47 blockade controls glioma

Phagocytic immunotherapies such as CD47 blockade have emerged as promising strategies for glioblastoma (GB) therapy, but the blood brain/tumor barriers (BBB/BTB) pose a persistent challenge for mCD47 delivery that can be overcome by focused ultrasound (FUS)-mediated BBB/BTB disruption. We here leverage immuno-PET imaging to determine how timing of [89Zr]-mCD47 injection relative to FUS impacts antibody penetrance into orthotopic murine gliomas. We then design and implement a rational paradigm for combining FUS and mCD47 for glioma therapy. We demonstrate that timing of antibody injection relative to FUS BBB/BTB disruption is a critical determinant of mCD47 access, with post-FUS injection conferring superlative antibody delivery to gliomas. We also show that mCD47 delivery across the BBB/BTB with repeat sessions of FUS can significantly constrain tumor outgrowth and extend survival in glioma-bearing mice. This study generates provocative insights for ongoing pre-clinical and clinical evaluations of FUS-mediated antibody delivery to brain tumors. Moreover, our results confirm that mCD47 delivery with FUS is a promising therapeutic strategy for GB therapy.

Interaction between AT1 and AT2 receptors during postinfarction left ventricular remodeling

The relative contribution of the angiotensin II type 1 and 2 receptors (AT1-R and AT2-R) in postmyocardial infarction (MI) remodeling remains incompletely understood. We studied five groups of C57Bl/6 mice after 1 h of left anterior descending artery occlusion-reperfusion: 1) wild type, untreated ( n = 12); 2) wild type, treated with the AT1-R blocker losartan (10–20 mg·kg−1·day−1 in drinking water) from day 1 to day 28 post-MI ( n = 10); 3) cardiac overexpression of the AT2-R [AT2-transgenic (TG); n = 14]; 4) AT2-TG treated with losartan ( n = 13); and 5) AT2-TG and null for the AT1a-R [AT2-TG/AT1 knockout (KO); n = 10]. Cardiac magnetic resonance imaging (CMR) measured ejection fraction and left ventricular end-diastolic and end-systolic volume (EDVI and ESVI) and mass indexed to weight on days 0, 1, 7, and 28 post-MI. Infarct size was measured on day 1 by late gadolinium-enhanced CMR. Regional myocyte hypertrophy and collagen content were measured on day 28 post-MI. Infarct size was similar among groups. Systolic blood pressure was lowest in AT2-TG/AT1KO. By day 28 post-MI, when corrected for baseline differences, EDVI and ESVI were higher and ejection fraction was lower in wild type than other groups. Ejection fraction was highest and EDVI and mass index were lowest in AT2-TG/AT1KO at day 28. The AT2-TG/AT1KO demonstrated less fibrosis in adjacent regions. Regional myocyte hypertrophy was similar in all groups. The AT1-R and AT2-R are intricately intertwined in post-MI remodeling. Pharmacological blockade of AT1-R is equivalent to AT2-R overexpression in attenuating post-MI remodeling. Genetic knockout of the AT1a-R is additive to AT2-R overexpression, due, at least in part, to blood pressure lowering.

Gender differences in leptin levels during puberty are related to the subcutaneous fat depot and sex steroids

Little is known about the influence of adiposity and hormone release on leptin levels in children and adolescents. We utilized criterion methods to examine the relationships among sex steroids, body composition (4 compartment), abdominal visceral and subcutaneous fat (magnetic resonance imagery), total subcutaneous fat (sum of 9 skinfolds), energy expenditure (doubly labeled water), aerobic fitness, and serum leptin levels in prepubertal and pubertal boys (n = 16; n = 13) and girls (n = 12; n = 15). The sum of skinfolds accounted for more variance in leptin levels of all girls [coefficient of determination (R2) = 0.70, P < 0.001] and all boys (R2 = 0.60, P < 0.001) than the total fat mass (girls, R2 = 0.52, P < 0.001; boys, R2 = 0.23, P < 0.001). Total energy expenditure, corrected for the influence of fat-free mass, correlated inversely with leptin (R2 = 0.18, P = 0.02). Gender differences in leptin disappeared when corrected for sex steroid levels or the combination of adiposity and energy expenditure. In multiple regression, the sum of skinfolds and free testosterone and estrogen levels accounted for 74% of the variance in leptin levels. We conclude that serum leptin levels are positively related to subcutaneous adiposity but negatively related to androgen levels. Energy expenditure may be negatively related to leptin levels by reduction of the adiposity, or a common genetic factor may influence both the activity and serum leptin levels.

Noninvasive in vivo magnetic resonance imaging of injury-induced neointima formation in the carotid artery of the apolipoprotein-E null mouse

Mice deficient in apolipoprotein-E (apoE) experience severe hypercholesterolemia, are prone to atherosclerosis, and recently have emerged as a powerful tool in the study of plaque formation. In this study, we developed magnetic resonance (MR) imaging methods to detect the progression of atherosclerosis noninvasively in a mouse model of arterial injury. Four 14-week-old apoE-deficient mice were imaged 5 weeks after beginning an atherogenic Western diet and 4 weeks after wire denudation injury of the left common carotid artery (LCCA). Information from several images was combined into high-information content images using methods previously developed. The image resolution was 47 x 47 x 750 microm(3). We acquired T1-, T2-, and proton density (PD)-weighted images (TR/TE 650/14, 2000/60, and 2000/14 msec, respectively). Each 8-bit image was placed in a separate color channel to produce a 24-bit color image (red = T1, green = PD, and blue = T2). The composite image created contrast between different tissue types that was superior to that of any single image and revealed significant luminal narrowing of the LCCA, but not the uninjured RCCA. MR images were compared with corresponding histopathology cross sections and luminal area measurements from each method correlated(r2= 0.61). Atherosclerotic luminal narrowing was successfully detected through MR imaging in a mouse model of arterial injury that is small, reproduces quickly, and lends itself to genetic analysis and manipulation.

MR imaging of the liver: breath-hold T1-weighted MP-GRE compared with conventional T2-weighted SE imaging--lesion detection, localization, and characterization

PURPOSE

To compare breath-hold T1-weighted magnetization-prepared gradient-echo (MP-GRE) imaging with conventional T2-weighted spin-echo (SE) imaging in evaluation of focal liver disease.

MATERIALS AND METHODS

Images of 68 patients evaluated for focal liver disease were reviewed. Five sets of images were analyzed: axial, sagittal, and coronal breath-hold T1-weighted MP-GRE images, axial T2-weighted SE images, and a compilation of axial, sagittal, and coronal (three-plane) T1-weighted MP-GRE images. Lesion signal intensity (SI) and signal difference-to-noise (SD/N) ratios were calculated.

RESULTS

Lesions were detected, localized, and characterize more accurately (P < .05-.001) and with greater confidence on three-plane T1-weighted MP-GRE images than on almost all single-plane images. Mean SI ratios of nonsolid and solid lesions on MP-GRE and SE images were significantly different at all lesion sizes; mean SD/N ratio was significantly different only for large lesions.

CONCLUSION

Lesion detection, localization, and characterization can be accurately and confidently performed with three-plane T1-weighted MP-GRE breath-hold imaging, potentially obviating conventional T2-weighted SE imaging.

Low-density lipoprotein lowering does not improve calf muscle perfusion, energetics, or exercise performance in peripheral arterial disease

OBJECTIVES

We hypothesized that low-density lipoprotein (LDL) reduction regardless of mechanism would improve calf muscle perfusion, energetics, or walking performance in peripheral arterial disease (PAD) as measured by magnetic resonance imaging and magnetic resonance spectroscopy.

BACKGROUND

Statins improve cardiovascular outcome in PAD, and some studies suggest improved walking performance.

METHODS

Sixty-eight patients with mild to moderate symptomatic PAD (age 65 ± 11 years; ankle-brachial index [ABI] 0.69 ± 0.14) were studied at baseline and annually for 2 years after beginning simvastatin 40 mg (n = 20) or simvastatin 40 mg/ezetimibe 10 mg (n = 18) if statin naïve, or ezetimibe 10 mg (n = 30) if taking a statin. Phosphocreatine recovery time was measured by (31)P magnetic resonance spectroscopy immediately after symptom-limited calf exercise on a 1.5-T scanner. Calf perfusion was measured using first-pass contrast-enhanced magnetic resonance imaging with 0.1 mM/kg gadolinium at peak exercise. Gadolinium-enhanced magnetic resonance angiography was graded. A 6-min walk and a standardized graded Skinner-Gardner exercise treadmill test with peak Vo(2) were performed. A repeated-measures model compared changes over time.

RESULTS

LDL reduction from baseline to year 2 was greater in the simvastatin 40 mg/ezetimibe 10 mg group (116 ± 42 mg/dl to 56 ± 21 mg/dl) than in the simvastatin 40 mg group (129 ± 40 mg/dl to 90 ± 30 mg/dl, p < 0.01). LDL also decreased in the ezetimibe 10 mg group (102 ± 28 mg/dl to 79 ± 27 mg/dl, p < 0.01). Despite this, there was no difference in perfusion, metabolism, or exercise parameters between groups or over time. Resting ABI did improve over time in the ezetimibe 10 mg group and the entire study group of patients.

CONCLUSIONS

Despite effective LDL reduction in PAD, neither tissue perfusion, metabolism, nor exercise parameters improved, although rest ABI did. Thus, LDL lowering does not improve calf muscle physiology or functional capacity in PAD. (Comprehensive Magnetic Resonance of Peripheral Arterial Disease; NCT00587678).

The angiotensin II type 2 receptor and improved adjacent region function post-MI

Angiotensin II type 2 receptor (AT2-R) overexpression in the mouse heart preserves left ventricular (LV) size and global LV function during post-MI remodeling. We hypothesized that CMR tagging would localize regional improvements in myocardial function during post-MI remodeling in AT2-R cardiac overexpressed transgenic mice (TG), which could explain the preservation of global LV function post-MI. Six male wild-type (WT) C57BL/6 mice and 10 TG mice were studied by CMR at baseline (day 0) and days 1, 7, and 28 post-MI. MI was induced by 1 hour occlusion of the LAD followed by reperfusion. On day 1 post-MI, gadolinium-DTPA was injected to assess infarct size. LV size and function was assessed by cine CMR. Mean % circumferential shortening (%CS) was calculated within infarcted, adjacent, and remote regions at each time point in WT and TG mice. Quantitative interstitial collagen and mean myocyte cross-sectional area was measured postmortem at day 28 post-MI. LV end-systolic volume was lower and ejection fraction higher at baseline in the TG group and these differences were maintained post-MI. Within infarcted and remote zones, although %CS was higher in TG mice at day 0, there was no difference by day 28 between groups. Within adjacent regions, while there was no difference at day 0 or 1 in TG vs. WT, %CS was significantly higher in TG mice by day 7, and these changes persisted out to day 28 post-MI. Regional interstitial collagen and myocyte size were similar between groups. Thus, myocardial tagging can detect regional differences in contractile function post-MI in TG mice, and AT2-R overexpression is associated with improved contractile function in adjacent noninfarcted myocardium.

Topoisomerase Inhibition Accelerates Gene Expression after Adeno-associated Virus-mediated Gene Transfer to the Mammalian Heart

Utility of adeno-associated virus 2 (AAV2) vectors for cardiac gene therapy is limited by the prolonged lag phase before maximal gene expression. Topoisomerase inhibition can induce AAV2-mediated gene expression in vivo, but with variable success in different tissues. In this study, we demonstrate that topoisomerase inhibition can accelerate AAV2-mediated gene expression in the mouse heart. We used an AAV2 vector expressing firefly luciferase and monitored expression kinetics using non-invasive bioluminescence imaging. In the group receiving vector alone, cardiac luciferase activity was evident from week 2 onward and increased progressively to reach a steady plateau by 9 weeks postinjection. In the group receiving vector and camptothecine (CPT), luciferase expression was evident from days 2 to 4 onward and increased rapidly to reach a steady plateau by 3-4 weeks postinjection, nearly three times faster than in the absence of CPT (P<0.05). Southern blot analysis of AAV2 genomes in cardiac tissue showed rapid conversion of the AAV2 genome from its single-stranded to double-stranded form in CPT-treated mice. Non-invasive determinations of luciferase expression correlated well with in vitro luciferase assays. Direct injection of the AAV2 vector and long-term luciferase gene expression had no detectable effects on normal cardiac function as assessed by magnetic resonance imaging.

Determination of intracranial tumor volumes in a rodent brain using magnetic resonance imaging, Evans blue, and histology: a comparative study

The measurement of tumor volumes is a practical and objective method of assessing the efficacy of a therapeutic agent. However, the relative accuracy of different methods of assessing tumor volume has been unclear. Using T1-weighted, gadolinium-enhanced magnetic resonance Imaging (T1-MRI), Evans Blue infusion and histology we measured intracranial tumor volumes in a rodent brain tumor model (RT2) at days 10, 16 and 18 after implantation of cells in the caudate putamen. There is a good correlation between tumor volumes comparing T1-MRI and Evans Blue (r2 = 0.99), T1-MRI and Histology (r2 = 0.98) and histology and Evans Blue (r2 = 0.93). Each of these methods is reliable in estimating tumor volumes in laboratory animals. There was significant uptake of gadolinium and Evans Blue in the tumor suggesting a wide disruption of the blood-brain barrier.

Occlusion of the anterior cerebral artery after Gamma Knife irradiation in a rat

The anterior cerebral artery of rats was irradiated at the level of the circle of Willis by Gamma Knife with a maximum dose of 25, 50, or 100 Gy. Occlusion of the anterior cerebral artery was observed in one rat which was followed for 20 months after irradiation of 100 Gy. Cerebral infarction was found at the midline-frontal region and the cingulate gyrus. Arterial wall thickening with fibrosis, splitting of the internal elastic membrane, luminal organized thrombus, and migration of smooth muscle cells into the thrombus were observed. In the anterior cerebral artery, thrombus formation seemed to occur after the endothelial injury and this may play a prominent role for occlusion. In small arteries, various changes were observed in the irradiated tissue. These included fibrosis and thrombus, thickened smooth muscle layer, lymphocytic infiltration, and thickening of vessel wall with fibrosis and fibrinous thrombosis with leakage of fibrin into the surrounding tissue after different doses of radiation and at different observation times. These changes were comparable to the ordinary vascular response to injury including healing vasculitis and arteriosclerosis.

Detection of regional pulmonary perfusion deficit of the occluded lung using arterial spin labeling in magnetic resonance imaging

Detection of regional perfusion deficit in the lung has been demonstrated using an arterial spin labeling technique called flow-sensitive alternating inversion recovery with an extra radiofrequency pulse (FAIRER). A pulmonary artery was occluded using a nondetachable balloon catheter to simulate an acute pulmonary embolism in 3 of 10 rabbits. Inflating the balloon occludes the artery, and deflating the balloon allows for reperfusion. Perfusion imaging was performed pre-occlusion, during occlusion, and after reperfusion. Signal enhancement due to perfusion of the pulmonary parenchyma was observed in the perfusion images with negligible artifacts. The perfusion deficit of the pulmonary parenchyma was detected distal to the site of occlusion in all three rabbits. Return of the pulmonary parenchymal perfusion was observed after reperfusion. Magnetic resonance imaging using FAIRER can detect signal loss due to absence of perfusion caused by pulmonary embolism.

Contrast-Enhanced MR Angiography at 1.5 T After Implantation of Platinum Stents: In Vitro and In Vivo Comparison with Conventional Stent Designs

OBJECTIVE

The objective of our study was to evaluate the in vitro and in vivo 3D contrast-enhanced MR angiography characteristics of a new platinum-based balloon-expandable stent system and compare this system with a variety of competing metallic stents.

MATERIALS AND METHODS

All experiments were performed on 1.5-T scanners. In vitro experiments were performed using 10 stents implanted into a custom-built phantom. Different orientations of the stents along the magnetic field and multiple flip angles were examined. In addition, 19 patients underwent contrast-enhanced MR angiography after the implantation of 36 stents, including four patients with six platinum stents. Angiographic correlation was available for all 19 patients, and luminal patency and stent-induced artifacts were assessed quantitatively.

RESULTS

Of the tested balloon-expandable stents, only the platinum-based stents created artifact causing luminal narrowing of 30% or less. All other balloon-expandable stents induced larger artifacts that resulted in higher degrees of narrowing. Thus, if patent, the platinum-based stents allow significant in-stent stenosis to be ruled out reliably. Selected nitinol- or tantalum-based self-expandable stents also are suitable in this regard.

CONCLUSION

Of the tested devices, platinum-based stents are the only type of currently available balloon-expandable stent that creates 30% or less artifact-induced apparent stenosis and thus are suitable for MR angiography.

Comparison of first-pass Gd-DOTA and FAIRER MR perfusion imaging in a rabbit model of pulmonary embolism

PURPOSE

To compare the sensitivity of contrast-enhanced magnetic resonance imaging (MRI) and arterial spin labeling to perfusion deficits in the lung.

MATERIALS AND METHODS

A rabbit model of pulmonary embolism was imaged with both flow-sensitive alternating inversion recovery with an extra radiofrequency pulse (FAIRER) arterial spin labeling and Gd-DOTA enhanced MRI. The signal-to-noise ratio (SNR) was measured in the area of the perfusion deficit and the normal lung for both techniques.

RESULTS

The defect was readily visible in all images. The normal lung had an average of 3.8 +/- 1.2 times the SNR of the unperfused lung with the arterial spin labeling technique, and approximately 13.7 +/- 3.3 times the SNR with the contrast-enhanced technique.

CONCLUSION

Gd-DOTA enhanced MRI provides higher SNR in pulmonary perfusion imaging; however, arterial spin labeling is also adequate and may be used when repeated studies are indicated.

Focal liver disease: comparison of breath-hold T1-weighted MP-GRE MR imaging and contrast-enhanced CT--lesion detection, localization, and characterization

PURPOSE

To compare breath-hold T1-weighted magnetization-prepared gradient-echo (MP-GRE) magnetic resonance (MR) imaging with contrast material-enhanced computed tomography (CT) in the assessment of focal liver disease.

MATERIALS AND METHODS

The MR and CT images obtained in 64 patients with focal liver disease were reviewed by six independent reviewers in a randomized, blinded fashion. Sets of axial T1-weighted MP-GRE images, three-plane (a compilation of axial, sagittal, and coronal) T1-weighted MP-GRE images, and contrast-enhanced CT scans were analyzed. T2-weighted spin-echo (SE) MR images were also compared with CT scans.

RESULTS

Lesions were detected, localized, and characterized more accurately and generally with greater confidence with three-plane T1-weighted MP-GRE imaging than with CT (P < .01). Axial T1-weighted MP-GRE imaging was also superior (P < .05) to CT (although slightly less superior than three-plane imaging) except in the characterization of specific lesions, where both techniques were equal. T2-weighted SE MR imaging and CT were about equal.

CONCLUSION

Lesion detection, localization, and characterization are performed more accurately and confidently with breath-hold T1-weighted MP-GRE imaging than with contrast-enhanced CT, particularly when breath-hold images are obtained in three planes.

Synthesis of novel neutrophil-specific imaging agents for Positron Emission Tomography (PET) imaging

A neutrophil-specific peptide, cinnamoyl-F(D)LF(D)LFK (cFLFLFK), was conjugated consecutively with a polyethylene glycol moiety (3.4K) and 2,2',2'',2'''-(1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrayl)tetraacetic acid (DOTA) to form cFLFLFK-PEG-DOTA. After (64)Cu labeling, Positron Emission Tomography (PET) imaging was successfully able to detect mouse lung inflammation.

Percutaneous intervention in peripheral artery disease improves calf muscle phosphocreatine recovery kinetics: a pilot study

We hypothesized that percutaneous intervention in the affected lower extremity artery would improve calf muscle perfusion and cellular metabolism in patients with claudication and peripheral artery disease (PAD) as measured by magnetic resonance imaging (MRI) and spectroscopy (MRS). Ten patients with symptomatic PAD (mean ± SD: age 57 ± 9 years; ankle-brachial index (ABI) 0.62 ± 0.17; seven males) were studied 2 months before and 10 months after lower extremity percutaneous intervention. Calf muscle phosphocreatine recovery time constant (PCr) in the revascularized leg was measured by (31)P MRS immediately after symptom-limited exercise on a 1.5-T scanner. Calf muscle perfusion was measured using first-pass gadolinium-enhanced MRI at peak exercise. A 6-minute walk and treadmill test were performed. The PCr recovery time constant improved significantly following intervention (91 ± 33 s to 52 ± 34 s, p < 0.003). Rest ABI also improved (0.62 ± 0.17 to 0.93 ± 0.25, p < 0.003). There was no difference in MRI-measured tissue perfusion or exercise parameters, although the study was underpowered for these endpoints. In conclusion, in this pilot study, successful large vessel percutaneous intervention in patients with symptomatic claudication, results in improved ABI and calf muscle phosphocreatine recovery kinetics.