Incidence of actionable findings on contrast enhanced magnetic resonance angiography ordered for pulmonary embolism evaluation.

PURPOSE: To determine the incidence of actionable findings on contrast-enhanced magnetic resonance angiography (MRA) scans performed for the primary diagnosis of pulmonary embolism (PE). MATERIALS AND METHODS: This was a HIPAA-compliant and IRB-approved single center, retrospective study of consecutive series of patients evaluated with contrast-enhanced MRA for PE. The final radiology report of each MRA was reviewed. All technically adequate negative exams were included in the analysis. The findings were divided into three types: those requiring further action (actionable-Type 1) those not requiring follow-up (non-actionable-Type 2) and normal exams. We compared our results with the literature regarding the use of computed tomographic angiography (CTA) in this scenario using Fisher's exact test. RESULTS: 580 MRA scans for PE were performed. There were 561/580 (97%) technically adequate exams. Of these, 514/580 (89%) were negative and 47/580 (8%) were positive for PE. In the PE negative group of 514 exams, Type 1 findings were identified in 85/514 (17%), 188/514 (36%) cases were Type 2 and 241/514 (47.0%) were Type 3. There was no significant difference between the incidence of Type 1 and the combination of Type 2 and Type 3 findings on MRA and the reported incidence of actionable findings derived from CTA negative exams for PE (p<0.5). CONCLUSION: MRA as a first-line test for PE can identify actionable findings in those patients without PE, with an incidence similar to that reported in the literature for CTA.

Longitudinal Assessment of Renal Perfusion and Oxygenation in Transplant Donor-Recipient Pairs Using Arterial Spin Labeling and Blood Oxygen Level-Dependent Magnetic Resonance Imaging.

OBJECTIVES: The aims of this study were to assess renal function in kidney transplant recipients and their respective donors over 2 years using arterial spin labeling (ASL) and blood oxygen level-dependent (BOLD) magnetic resonance imaging (MRI) and to prospectively evaluate the effect of losartan on functional MRI measures in recipients. MATERIALS AND METHODS: The study included 15 matched pairs of renal transplant donors and recipients. Arterial spin labeling and BOLD MRI of the kidneys were performed on donors before transplant surgery (baseline) and on both donors and recipients at 3 months, 1 year, and 2 years after transplant. After 3 months, 7 of the 15 recipients were prescribed 25 to 50 mg/d losartan for the remainder of the study. A linear mixed-effects model was used to evaluate perfusion, R2*, estimated glomerular filtration rate, and fractional excretion of sodium for changes across time or associated with losartan treatment. RESULTS: In donors, cortical perfusion in the remaining kidney decreased by 50 ± 19 mL/min per 100 g (11.8%) between baseline and 2 years (P < 0.05), while cortical R2* declined modestly by 0.7 ± 0.3 s-1 (5.6%; P < 0.05). In transplanted kidneys, cortical perfusion decreased markedly by 141 ± 21 mL/min per 100 g (34.2%) between baseline and 2 years (P < 0.001), while medullary R2* declined by 1.5 ± 0.8 s-1 (8.3%; P = 0.06). Single-kidney estimated glomerular filtration rate increased between baseline and 2 years by 17.7 ± 2.7 mL/min per 1.73 m (40.3%; P < 0.0001) in donors and to 14.6 ± 4.3 mL/min per 1.73 m (33.3%; P < 0.01) in recipients. Cortical perfusion at 1 and 2 years in recipients receiving 25 to 50 mg/d losartan was 62 ± 24 mL/min per 100 g higher than recipients not receiving the drug (P < 0.05). No significant effects of losartan were observed for any other markers of renal function. CONCLUSIONS: The results suggest an important role for noninvasive functional monitoring with ASL and BOLD MRI in kidney transplant recipients and donors, and they indicate a potentially beneficial effect of losartan in recipients.

Measurements of wall shear stress and aortic pulse wave velocity in swine with familial hypercholesterolemia.

PURPOSE: To assess measurements of pulse wave velocity (PWV) and wall shear stress (WSS) in a swine model of atherosclerosis. MATERIALS AND METHODS: Nine familial hypercholesterolemic (FH) swine with angioplasty balloon catheter-induced atherosclerotic lesions to the abdominal aorta (injured group) and 10 uninjured FH swine were evaluated with a 4D phase contrast (PC) magnetic resonance imaging (MRI) acquisition, as well as with radial and Cartesian 2D PC acquisitions, on a 3T MR scanner. PWV values were computed from the 2D and 4D PC techniques, compared between the injured and uninjured swine, and validated against reference standard pressure probe-based PWV measurements. WSS values were also computed from the 4D PC MRI technique and compared between injured and uninjured groups. RESULTS: PWV values were significantly greater in the injured than in the uninjured groups with the 4D PC MRI technique (P = 0.03) and pressure probes (P = 0.02). No significant differences were found in PWV between groups using the 2D PC techniques (P = 0.75-0.83). No significant differences were found for WSS values between the injured and uninjured groups. CONCLUSION: The 4D PC MRI technique provides a promising means of evaluating PWV and WSS in a swine model of atherosclerosis, providing a potential platform for developing the technique for the early detection of atherosclerosis.

Quantitative MR measures of intrarenal perfusion in the assessment of transplanted kidneys: initial experience.

RATIONALE AND OBJECTIVES: The purpose of this study was to evaluate prospectively a gadolinium-based perfusion technique for intrarenal blood flow in transplanted kidneys and to determine if magnetic resonance imaging (MRI) measurements of intrarenal perfusion could be used to differentiate between normal-functioning kidney allografts and allografts with acute tubular necrosis (ATN) or acute rejection. MATERIALS AND METHODS: Twenty-one subjects were enrolled within 4 months of receiving a kidney transplant. A biopsy was performed on subjects to diagnose each allograft as having either ATN or acute rejection. A group of subjects with normal functioning transplants was also enrolled in our study. MRI perfusion images were acquired on a 1.5 T MRI system within 48 hours after biopsy using an echo planar, T2*-weighted sequence, and an injection of gadodiamide contrast agent administered at a dose of 0.1 mmol/kg. Scan parameters were: repetition time/echo time/flip = 1000 ms/30 ms/60 degrees , field of view = 340 x 340 mm, matrix = 128 x 64, slice thickness = 10 mm, and temporal resolution = 1.0 seconds. Cortical and medullary blood flow values were calculated. RESULTS: Medullary blood flow values were significantly (P = .02) lower in allografts undergoing acute rejection (121 +/- 41 mL/100 g/min) compared to normal-functioning allografts (221 +/- 96 mL/100 g/min) and those with ATN (247 +/- 124 mL/100 g/min). Cortical blood flow values were also significantly (P = .03) reduced in allografts with acute rejection (243 +/- 116 mL/100 g/min) compared to those with normal function (413 +/- 116 mL/100 g/min). CONCLUSIONS: Preliminary results indicate that MRI perfusion techniques may provide a means of determining noninvasively the viability of renal allografts, potentially alleviating the need for biopsy in some patients.

Functional lung imaging using hyperpolarized gas MRI.

The noninvasive assessment of lung function using imaging is increasingly of interest for the study of lung diseases, including chronic obstructive pulmonary disease (COPD) and asthma. Hyperpolarized gas MRI (HP MRI) has demonstrated the ability to detect changes in ventilation, perfusion, and lung microstructure that appear to be associated with both normal lung development and disease progression. The physical characteristics of HP gases and their application to MRI are presented with an emphasis on current applications. Clinical investigations using HP MRI to study asthma, COPD, cystic fibrosis, pediatric chronic lung disease, and lung transplant are reviewed. Recent advances in polarization, pulse sequence development for imaging with Xe-129, and prototype low magnetic field systems dedicated to lung imaging are highlighted as areas of future development for this rapidly evolving technology.

BOLD-MRI assessment of intrarenal oxygenation and oxidative stress in patients with chronic kidney allograft dysfunction.

Blood oxygen level-dependent (BOLD) magnetic resonance imaging (MRI) uses deoxyhemoglobin as an endogenous contrast agent for the noninvasive assessment of tissue oxygen bioavailability. We hypothesized that intrarenal oxygenation was impaired in patients with chronic allograft nephropathy (CAN). Ten kidney-transplant recipients with CAN and nine healthy volunteers underwent BOLD-MRI. Medullary R2* (MR2*) and cortical R2* (CR2*) levels (measures directly proportional to tissue deoxyhemoglobin levels) were determined alongside urine and serum markers of oxidative stress (OS): hydrogen peroxide (H(2)O(2)), F(2)-isoprostanes, total nitric oxide (NO), heat shock protein 27 (HSP27), and total antioxidant property (TAOP). Mean MR2* and CR2* levels were significantly decreased in CAN (increased local oxyhemoglobin concentration) compared with healthy volunteers (20.7 +/- 1.6 vs. 23.1 +/- 1.8/s, P = 0.03 and 15.9 +/- 1.9 vs. 13.6 +/- 2.3/s, P = 0.05, respectively). There was a significant increase in serum and urine levels of H(2)O(2) and serum HSP27 levels in patients with CAN. Conversely, urine NO levels and TAOP were significantly increased in healthy volunteers. Multiple linear regression analyses showed a significant association between MR2* and CR2* levels and serum/urine biomarkers of OS. BOLD-MRI demonstrated significant changes in medullary and cortical oxygen bioavailability in allografts with CAN. These correlated with serum/urine biomarkers of OS, suggesting an association between intrarenal oxygenation and OS.

Noninvasive assessment of early kidney allograft dysfunction by blood oxygen level-dependent magnetic resonance imaging.

BACKGROUND: Blood oxygen level-dependent (BOLD) magnetic resonance imaging (MRI) is a noninvasive method to assess tissue oxygen bioavailability, using deoxyhemoglobin as an endogenous contrast agent. We hypothesized that BOLD-MRI could accurately discriminate different types of rejection early after kidney transplantation. METHODS: Twenty-three patients underwent imaging in the first four months posttransplant. Five had normal functioning transplants and 18 had biopsy-proven acute allograft dysfunction (acute tubular necrosis [ATN, n=5] and acute rejection [n=13] including borderline rejection: n=3; IA rejection: n=4; IIA rejection: n=6: C4d(+) rejection: n=9). RESULTS: Mean medullary R2* (MR2*) levels (a measure directly proportional to tissue deoxyhemoglobin levels) were significantly higher in normal functioning allografts (R2*=24.3/s+/-2.3) versus acute rejection (R2*=16.6/s+/-2.1) and ATN (R2*=20.9/s+/-1.8) (P<0.05). The lowest MR2* levels were observed in acute rejection episodes with vascular injury i.e. IIA and C4d (+). Similarly, the lowest medullary to cortical R2* ratios (MCR2*) were present in allografts with IIA (1.24+/-0.05) and C4d(+) rejection (1.26+/-0.06). ROC curve analyses suggested that MR2* and MCR2* values could accurately discriminate acute rejection in the early posttransplant period. CONCLUSIONS: BOLD-MRI demonstrated significant changes in medullary oxygen bioavailability in allografts with biopsy-proven ATN and acute rejection, suggesting that there may be a role for this noninvasive tool to evaluate kidney function early after transplantation.

Early emphysematous changes in asymptomatic smokers: detection with 3He MR imaging.

PURPOSE: To prospectively compare apparent diffusion coefficient (ADC) measurements derived from diffusion-weighted hyperpolarized helium 3 (3He) magnetic resonance (MR) imaging with functional and structural findings using spirometric tests and thin-section computed tomography (CT) of the lungs in asymptomatic smokers and healthy nonsmokers of similar age. MATERIALS AND METHODS: All studies were HIPAA compliant and were approved by the institutional review board. Informed consent was obtained. Ventilation and diffusion-weighted 3He MR images were obtained in healthy subjects: 11 smokers (five women, six men; mean age, 47 years+/-18 [standard deviation]; range, 23-73 years) and eight nonsmokers (<100 cigarettes in lifetime) (four women, four men; mean age, 46 years+/-16; range, 23-69 years). Mean ADC values for smokers and nonsmokers were compared with spirometric values, diffusing capacity of the lung for carbon monoxide (Dlco), age, and pack-years with Spearman rank correlation coefficient (rs) and multiple linear regression analysis. Mean ADC value and thin-section CT emphysema index of relative area less than -950 HU (RA950) were compared on a regional basis by using linear mixed-effect models. RESULTS: Mean ADC values and number of pack-years were significantly correlated (rs=0.60; 95% confidence interval (CI): 0.21, 1.00; P=.007); relationship remained significant after adjustment for age (P=.003). Dlco was strongly correlated with pack-years (rs=-0.63; 95% CI: -0.97, -0.29; P=.004). Negative correlations between mean ADC values and percentage predicted Dlco (rs=-0.79; 95% CI: -0.93, -0.64; P<.001) and the ratio of forced expiratory volume in 1 second to forced vital capacity (rs=-0.72; 95% CI: -0.92, -0.52; P=.001) were statistically significant. Correlations between spirometric values or RA950 and number of pack-years were not significant (.05 level). CONCLUSION: Correlations between mean ADC values and pulmonary function test measurements for diagnosing emphysema, especially Dlco, were statistically significant.

Detection of age-dependent changes in healthy adult lungs with diffusion-weighted 3He MRI.

RATIONALE AND OBJECTIVES: To investigate changes in lung microstructure in healthy adult subjects with no smoking history using diffusion-weighted 3He MRI. MATERIALS AND METHODS: Diffusion magnetic resonance imaging using hyperpolarized helium 3 (3He) was applied to healthy volunteers to explore the dependence of lung microstructural changes with age, reflected by changes in the apparent diffusion coefficient (ADC) of 3He in lung air spaces. Data from three sites (University of Virginia (UVa), N = 25; University of Wisconsin (UW), N = 8; University of Nottingham (UN), N = 11) were combined in pooled analysis, including a total of N = 44 subjects (age range, 18-69 years; average age, 41.7 +/- 16.7 years). RESULTS: ADC was found to depend on age at all three sites (UW, R = +0.95, P = .0003; UVa, R = +0.74, P < .0001; UN, R = +0.96, P < .0001). Increases in mean ADCs with age appeared similar across sites (UW, +0.0017 cm2 s(-1) y(-1); UVa, +0.0015 cm2 s(-1) y(-1); pooled, +0.0015 cm2 s(-1) y(-1); P = .71). In a regional analysis performed on UW data, the increase in ADC affected all regions of the lung, but the apical and middle regions showed a greater increase compared with the base of the lung. CONCLUSION: Results suggest the observed age dependence of the ADC may be caused by changes in lung microstructure that increase alveolar volume during the aging process.

Assessment of acute renal transplant rejection with blood oxygen level-dependent MR imaging: initial experience.

PURPOSE: To prospectively assess the oxygenation state of renal transplants and determine the feasibility of using blood oxygen level-dependent (BOLD) magnetic resonance (MR) imaging to differentiate between acute tubular necrosis (ATN), acute rejection, and normal function. MATERIALS AND METHODS: This HIPAA-compliant study had institutional human subjects review committee approval, and written informed consent was obtained from all patients. BOLD MR imaging was performed in 20 patients (age range, 21-70 years) who had recently received renal transplants. Six patients had clinically normal functioning transplants, eight had biopsy-proved rejection, and six had biopsy-proved ATN. R2* (1/sec) measurements were obtained in the medulla and cortex of transplanted kidneys. R2* is a measure of the rate of signal loss in a specific region and is related to the amount of deoxyhemoglobin present. Statistical analysis was performed by using a two-sample t test. Threshold R2* values were identified to discriminate between transplanted kidneys with ATN, those with acute rejection, and those with normal function. RESULTS: R2* values for the medulla were significantly lower in the acute rejection group (R2* = 15.8/sec +/- 1.5) than in normally functioning transplants (R2* = 23.9/sec +/- 3.2) and transplants with ATN (R2* = 21.3/sec +/- 1.9). The differences between the acute rejection and normal function groups (P = .001), as well as between the acute rejection and ATN groups (P < .001), were significant. Acute rejection could be differentiated from normal function and ATN in all cases by using a threshold R2* value of 18/sec. R2* values for the cortex were higher in ATN (R2* = 14.2/sec +/- 1.4) than for normally functioning transplants (R2* = 12.7/sec +/- 1.6) and transplants with rejection (R2* = 12.4/sec +/- 1.2). The difference in R2* values in the cortex between ATN and rejection was statistically significant (P = .034), although there was no threshold value that enabled differentiation of all cases of ATN from cases of normal function or acute rejection. CONCLUSION: R2* measurements in the medullary regions of transplanted kidneys with acute rejection were significantly lower than those in normally functioning transplants or transplants with ATN. These results suggest that marked changes in intrarenal oxygenation occur during acute transplant rejection.