Assessment of cell infiltration in myocardial infarction: A dose‐dependent study using micrometer‐sized iron oxide particles

Myocardial infarction (MI) is a leading cause of death and disabilities. Inflammatory cells play a vital role in the process of postinfarction remodeling and repair. Inflammatory cell infiltration into the infarct site can be monitored using T‐weighted MRI following an intravenous administration of iron oxide particles. In this study, various doses of micrometer‐sized iron oxide particles (1.1–14.5 μg Fe/g body weight) were injected into the mouse blood stream before a surgical induction of MI. Cardiac MRIs were performed at 3, 7, 14, and 21 days postinfarction to monitor the signal attenuation at the infarct site. A dose‐dependent phenomenon of signal attenuation was observed at the infarct site, with a higher dose leading to a darker signal. The study suggests an optimal temporal window for monitoring iron oxide particles‐labeled inflammatory cell infiltration to the infarct site using MRI. The dose‐dependent signal attenuation also indicates an optimal iron oxide dose of approximately 9.1–14.5 μg Fe/g body weight. A lower dose cannot differentiate the signal attenuation, whereas a higher dose would cause significant artifacts. This iron oxide‐enhanced MRI technique can potentially be used to monitor cell migration and infiltration at the pathological site or to confirm any cellular response following some specific treatment strategies. Magn Reson Med, 2011. © 2011 Wiley Periodicals, Inc.     

Monitoring bone marrow‐originated mesenchymal stem cell traffic to myocardial infarction sites using magnetic resonance imaging

How stem cells promote myocardial repair in myocardial infarction (MI) is not well understood. The purpose of this study was to noninvasively monitor and quantify mesenchymal stem cells (MSC) from bone marrow to MI sites using magnetic resonance imaging (MRI). MSC were dual‐labeled with an enhanced green fluorescent protein and micrometer‐sized iron oxide particles prior to intra‐bone marrow transplantation into the tibial medullary space of C57Bl/6 mice. Micrometer‐sized iron oxide particles labeling caused signal attenuation in T₂*‐weighted MRI and thus allowed noninvasive cell tracking. Longitudinal MRI demonstrated MSC infiltration into MI sites over time. Fluorescence from both micrometer‐sized iron oxide particles and enhanced green fluorescent protein in histology validated the presence of dual‐labeled cells at MI sites. This study demonstrated that MSC traffic to MI sites can be noninvasively monitored in MRI by labeling cells with micrometer‐sized iron oxide particles. The dual‐labeled MSC at MI sites maintained their capability of proliferation and differentiation. The dual‐labeling, intra‐bone marrow transplantation, and MRI cell tracking provided a unique approach for investigating stem cells' roles in the post‐MI healing process. This technique can potentially be applied to monitor possible effects on stem cell mobilization caused by given treatment strategies. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

Effectiveness of micron‐sized superparamagnetic iron oxide particles as markers for detection of migration of bone marrow‐derived mesenchymal stromal cells in a stroke model

Purpose:

To evaluate the feasibility of using micron‐sized superparamagnetic iron oxide particles (MPIOs) as an effective labeling agent for monitoring bone marrow‐derived mesenchymal stromal cell (BMSC) migration in the brain using magnetic resonance imaging (MRI) in a rat model of stroke and whether the accumulation of MPIO‐labeled BMSCs can be differentiated from the accumulation of free MPIO particles or hemoglobin breakdown at a site of neuronal damage.

Materials and Methods:

In this study BMSCs were labeled with iron oxide and their pattern of migration following intravenous injection in a rat stroke model was monitored using a clinical MRI system followed by standard histopathology. The migration pattern was compared between intravenous injection of BMSCs alone, BMSCs labeled with MPIOs, and MPIO particles alone.

Results:

The results demonstrated that while MRI was highly sensitive in the detection of iron oxide particle‐containing cells in areas of neuronal ischemia, the true origin of cells containing iron oxide particles remains ambiguous. Therefore, detection of iron particles may not be a suitable strategy for the detection of BMSCs in the brain in a stroke model.

Conclusion:

This study suggests that the use of MPIOs as labeling agents are insufficient to conclusively determine the localization of iron within cells in regions of neuronal ischemia and hemorrhage. J. Magn. Reson. Imaging 2013;37:1409–1418. © 2012 Wiley Periodicals, Inc.     

Indirectly probing Ca2+ handling alterations following myocardial infarction in a murine model using T1‐mapping manganese‐enhanced magnetic resonance imaging

Prolonged ischemia causes cellular necrosis and myocardial infarction (MI) via intracellular calcium (Ca²⁺) overload. Manganese‐enhanced MRI indirectly assesses Ca²⁺ influx movement in vivo as manganese (Mn²⁺) is a Ca²⁺ analog. To characterize myocardial Mn²⁺ efflux properties, T₁‐mapping manganese‐enhanced MRI studies were performed on adult male C57Bl/6 mice in which Ca²⁺ efflux was altered using pharmacological intervention agents or MI‐inducing surgery. Results showed that ( 1 ) Mn²⁺ efflux rate increased exponentially with increasing Mn²⁺ doses; ( 2 ) SEA0400 (a sodium–calcium exchanger inhibitor) decreased the rate of Mn²⁺ efflux; and ( 3 ) dobutamine (a positive inotropic agent) increased the Mn²⁺ efflux rate. A novel analysis technique also delineated regional features in the MI mice, which showed an increased Mn²⁺ efflux rate in the necrosed and peri‐infarcted tissue zones. The T₁‐mapping manganese‐enhanced MRI technique characterized alterations in myocardial Mn²⁺ efflux rates following both pharmacologic intervention and an acute MI. The Mn²⁺ efflux results were consistent with those in ex vivo studies showing an increased Ca²⁺ concentration under similar conditions. Thus, T₁‐mapping manganese‐enhanced MRI has the potential to indirectly identify and quantify intracellular Ca²⁺ handling in the peri‐infarcted tissue zones, which may reveal salvageable tissue in the post‐MI myocardium. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Improved arterial spin labeling after myocardial infarction in mice using cardiac and respiratory gated look‐locker imaging with fuzzy C‐means clustering

Experimental myocardial infarction (MI) in mice is an important disease model, in part due to the ability to study genetic manipulations. MRI has been used to assess cardiac structural and functional changes after MI in mice, but changes in myocardial perfusion after acute MI have not previously been examined. Arterial spin labeling noninvasively measures perfusion but is sensitive to respiratory motion and heart rate variability and is difficult to apply after acute MI in mice. To account for these factors, a cardiorespiratory‐gated arterial spin labeling sequence using a fuzzy C‐means algorithm to retrospectively reconstruct images was developed. Using this method, myocardial perfusion was measured in remote and infarcted regions at 1, 7, 14, and 28 days post‐MI. Baseline perfusion was 4.9 ± 0.5 mL/g·min and 1 day post‐MI decreased to 0.9 ± 0.8 mL/g·min in infarcted myocardium (P < 0.05 versus baseline) while remaining at 5.2 ± 0.8 mL/g·min in remote myocardium. During the subsequent 28 days, perfusion in the remote zone remained unchanged, while a partial recovery of perfusion in the infarct zone was seen. This technique, when applied to genetically engineered mice, will allow for the investigation of the roles of specific genes in myocardial perfusion during infarct healing. Magn Reson Med 63:648–657, 2010. © 2010 Wiley‐Liss, Inc.     

Fat‐water separated delayed hyperenhanced myocardial infarct imaging

Fat deposition associated with myocardial infarction (MI) has been reported as a commonly occurring phenomenon. Magnetic resonance imaging (MRI) has the ability to efficiently detect MI using T₁‐sensitive contrast‐enhanced sequences and fat via its resonant frequency shift. In this work, the feasibility of fat‐water separation applied to the conventional delayed hyperenhanced (DHE) MI imaging technique is demonstrated. A three‐point Dixon acquisition and reconstruction was combined with an inversion recovery gradient‐echo pulse sequence. This allowed fat‐water separation along with T₁ sensitive imaging after injection of a gadolinium contrast agent. The technique is demonstrated in phantom experiments and three subjects with chronic MI. Areas of infarction were well defined as conventional hyperenhancement in water images. In two cases, fatty deposition was detected in fat images and confirmed by precontrast opposed‐phase imaging. Magn Reson Med 60:503–509, 2008. © 2008 Wiley‐Liss, Inc.     

Flow‐sensitive four‐dimensional cine magnetic resonance imaging for offline blood flow quantification in multiple vessels: A validation study

Purpose:

To further validate the quantitative use of flow‐sensitive four‐dimensional velocity encoded cine magnetic resonance imaging (4D VEC MRI) for simultaneously acquired venous and arterial blood flow in healthy volunteers and for abnormal flow in patients with congenital heart disease.

Materials and Methods:

Stroke volumes (SV) obtained in arterial and venous thoracic vessels were compared between standard two‐dimensional (2D), 4D VEC MRI with and without respiratory navigator gating (gated/nongated) in volunteers (n = 7). In addition, SV and regurgitation fractions (RF) measured in aorta or pulmonary trunk of patients with malformed and/or insufficient valves (n = 10) were compared between 2D and nongated 4D VEC MRI methods.

Results:

In volunteers and patients, Bland–Altman tests showed excellent agreement between 2D, gated, and nongated 4D VEC MRI obtained quantitative blood flow measurements. The bias between 2D and gated 4D VEC MRI was <0.5 mL for SV; between 2D and nongated 4D VEC MRI the bias was <0.7 mL for SV and <1% for RF.

Conclusion:

Blood flow can be quantified accurately in arterial, venous, and pathological flow conditions using 4D VEC MRI. Nongated 4D VEC MRI has the potential to be suited for clinical use in patients with congenital heart disease who require flow acquisitions in multiple vessels. J. Magn. Reson. Imaging 2010;32:677–683. © 2010 Wiley‐Liss, Inc.     

Myocardial T2‐mapping and velocity mapping: Changes in regional left ventricular structure and function after heart transplantation

Monitoring post cardiac transplant (TX) status relies on frequent invasive techniques such as endomyocardial biopsies and right heart cardiac catheterization. The aim of this study was to noninvasively evaluate regional myocardial structure, function, and dyssynchrony in TX patients. Myocardial T2‐mapping and myocardial velocity mapping of the left ventricle (basal, midventricular, and apical short‐axis locations) was applied in 10 patients after cardiac transplantation (49 ± 13years, n = 2 with signs of mild rejection, time between TX and MRI = 1–64 months) and compared to healthy controls (n = 20 for myocardial velocity mapping and n = 14 for T2). Segmental analysis based on the 16‐segment American Heart Association model revealed increased T2 (P = 0.0003) and significant (P < 0.0001) reductions in systolic and diastolic radial and long‐axis peak myocardial velocities in TX patients without signs of rejection compared to controls. Multiple comparisons of individual left ventricular segments demonstrated reductions of long‐axis peak velocities in 50% of segments (P < 0.001) while segmental T2 values were not significantly different. Systolic radial as well as diastolic radial and long‐axis dyssynchrony were significantly (P < 0.04) increased in TX patients indicating less coordinated contraction, expansion, and lengthening. Correlation analysis revealed moderate but significant (P < 0.010) inverse relationships between myocardial T2 and long‐axis peak velocities suggesting a structure–function relationship between altered T2 and myocardial function. Magn Reson Med 70:517–526, 2013. © 2012 Wiley Periodicals, Inc.     

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

T₂‐weighted, cardiac magnetic resonance imaging (T₂w 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, T₂w CMR sequence to quantify the AAR in mouse models of ischemia and infarction. The ΔB₀ and ΔB₁ environment around the mouse heart at 7 T were measured, and a T₂‐preparation sequence suitable for these conditions was developed. Both in vivo T₂w 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 T₂w imaging method for mice may allow for future investigations of genetic manipulations and novel therapies affecting the AAR and salvaged myocardium following reperfused MI. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

Manganese‐enhanced MRI of salivary glands and head and neck tumors in living subjects

Manganese‐enhanced MRI has previously been used for visualization of brain architecture and functional mapping of neural pathways. The present work investigated the potential of manganese‐enhanced MRI for noninvasive imaging of salivary glands in living subjects. Marked shortening of T₁ was observed in salivary glands of naïve mice (n = 5) 24–48 h after systemic administration of MnCl₂ (0.4 mmol/kg, intraperitoneally). Three‐dimensional MR microscopy confirmed selective contrast enhancement of salivary gland tissues post–MnCl₂ injection. Ectopic and orthotopic head and neck tumor xenografts also showed an increase in R₁ at 24 h following MnCl₂ injection (0.2 mmol/kg, intraperitoneally). However, tumor enhancement was minimal compared to salivary gland tissue. Salivary gland R₁ values were lower in mice bearing orthotopic head and neck tumors compared to naïve mice. These results demonstrate, for the first time, the usefulness of manganese‐enhanced MRI in the visualization of salivary glands and head and neck tumors in vivo. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Imaging iron‐loaded mouse glioma tumors with bSSFP at 3 T

The poor prognosis for patients with high‐grade glioma is partly due to the invasion of tumor cells into surrounding brain tissue. The goal of the present work was to develop a mouse model of glioma that included the potential to track cell invasion using MRI by labeling GL261 cells with iron oxide contrast agents prior to intracranial injection. Two types of agents were compared with several labeling schemes to balance between labeling with sufficient iron to curb the dilution effect of cell division while avoiding overwhelming signal loss that could prevent adequate visualization of tumor boundaries. The balanced steady‐state free precession (bSSFP) pulse sequence was evaluated for its suitability for imaging glioma tumors and compared to T₂‐weighted two‐dimensional fast spin echo (FSE) and T₁‐weighted spoiled gradient recalled echo (SPGR) at 3 T in terms of signal‐to‐noise ratio and contrast‐to‐noise ratio efficiencies. Ultimately, a three‐dimensional bSSFP protocol consisting of a set of two images with complementary contrasts was developed, allowing excellent tumor visualization with minimal iron contrast when using pulse repetition time = 6 ms and α = 40°, and extremely high sensitivity to iron when using pulse repetition time = 22 ms and α = 20°. Quantitative histologic analysis validated that the strong signal loss seen in balanced steady state free precession pulse sequence images of iron‐loaded tumors correlated well with the presence of iron. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Preserved metabolic reserve capacity in skeletal muscle of post‐infarction heart failure patients

It has been proposed that exercise capacity during whole body exercise in post‐infarction congestive heart failure (CHF) patients is limited by skeletal muscle function. We therefore investigated the balance between cardiopulmonary and muscular metabolic capacity. CHF patients (n=8) and healthy subjects (HS, n=12) were included. Patients with coronary artery disease (CAD, n=8) were included as a control for medication. All subjects performed a stepwise incremental load test during bicycling (～24 kg muscle mass), two‐legged knee extensor (2‐KE) exercise (～4 kg muscle mass) and one‐legged knee extensor (1‐KE) exercise (～2 kg muscle mass). Peak power and peak pulmonary oxygen uptake (VO_2peak) increased and muscle‐specific VO_2peak decreased with an increasing muscle mass involved in the exercise. Peak power and VO_2peak were lower for CHF patients than HS, with values for CAD patients falling between CHF patients and HS. During bicycling, all groups utilized 24–29% of the muscle‐specific VO_2peak as measured during 1‐KE exercise, with no difference between the groups. Hence, the muscle metabolic reserve capacity during whole body exercise is not different between CHF patients and HS, indicating that appropriately medicated and stable post‐infarction CHF patients are not more limited by intrinsic skeletal muscle properties during whole body exercise than HS.     

Four‐dimensional velocity‐encoded magnetic resonance imaging improves blood flow quantification in patients with complex accelerated flow

Purpose:

To evaluate the use of four‐dimensional (4D) velocity‐encoded magnetic resonance imaging (VEC MRI) for blood flow quantification in patients with semilunar valve stenosis and complex accelerated flow.

Materials and Methods:

Peak velocities (Vmax) and stroke volumes (SV) were quantified by 2D and 4D VEC MRI in volunteers (n = 7) and patients with semilunar valve stenosis (n = 18). Measurements were performed above the aortic and pulmonary valve with both techniques and, additionally, at multiple predefined planes in the ascending aorta and in the pulmonary trunk within the 4D dataset. In patients, 4D VEC MRI streamline analysis identified flow patterns and regions of highest flow velocity (4D_{max‐targeted}) for further measurements and Vmax was also measured by Doppler‐echocardiography.

Results:

In patients, 4D VEC MRI showed higher Vmax than 2D VEC MRI (2.7 ± 0.6 m/s vs. 2.4 ± 0.5 m/s, P < 0.03) and was more comparable to Doppler‐echocardiography (2.8 ± 0.7 m/s). 4D_{max‐targeted} revealed highest Vmax values (3.1 ± 0.6 m/s). SV measurements showed significant differences between different anatomical levels in the ascending aorta in patients with complex accelerated flow, whereas differences in volunteers with laminar flow patterns were negligible (P = 0.004).

Conclusion:

4D VEC MRI improves MRI‐derived blood flow quantification in patients with semilunar valve stenosis and complex accelerated flow. J. Magn. Reson. Imaging 2013;37:208–216. © 2012 Wiley Periodicals, Inc.     

Vertebral blood perfusion reduction associated with vertebral bone mineral density reduction: A dynamic contrast‐enhanced MRI study in a rat orchiectomy model

Purpose

To investigate the relationship between vertebral blood perfusion and vertebral bone mineral density (BMD) in a rat orchiectomy (ORX) model.

Materials and Methods

Nine 6‐month‐old male Wistar‐Kyoto rats were used. Computed tomography (CT) bone densitometry and dynamic MRI were performed at baseline and four weeks post‐ORX. MRI was performed on a 1.5T clinical MR scanner with a small surface coil placed under the rat lumbar spine region. A sagittal midsection of the lumbar spine was prescribed. Dynamic MRI was performed after a bolus injection of gadolinium‐tetraazacyclododecane tetraacetic acid (Gd‐DOTA) (0.3 mmol/kg) administered through a tail vein cannula. At a temporal resolution of 0.6 seconds, 800 images were acquired. Regions‐of‐interest were drawn comprising the medullary component of lumbar vertebrae L3–L6. Maximum enhancement was analyzed.

Results

Satisfactory CT and MRI data for analysis was obtained in all animals. Vertebral BMD decreased by 16.6% at four weeks post‐ORX (1.134 ± 0.035 vs. 0.946 ± 0.027 g/cm³, P = 0.008). MRI maximum enhancement decreased by 17% at four weeks post‐ORX (151.5 ± 12.0% vs. 125.8 ± 9.9%, P = 0.015).

Conclusion

Vertebral blood perfusion reduction is associated with vertebral BMD reduction in a male rat osteoporosis model. Perfusion MRI provides a new investigative technique for osteoporosis experimental research. J. Magn. Reson. Imaging 2008;28:1515–1518. © 2008 Wiley‐Liss, Inc.     

Enhanced magnetic cell labeling efficiency using –NH2 coated MPIOs

Strategies have been developed for labeling cells with micron sized iron oxide particles (MPIOs) for in vivo visualization of cells by magnetic resonance imaging. Although this approach is well established and has a variety of applications, current protocols employ long labeling times. It has been previously demonstrated that incubation of dextran coated iron oxide nanoparticles with positively charged transfection agents, such as poly‐L ‐lysine increases labeling efficiency. Therefore, we sought to ascertain whether preincubating MPIOs with various quantities of poly‐L ‐lysine would similarly enhance the rate of magnetic cell labeling. This was also tested against an NH₂ functionalized, commercially available MPIO. Indeed, we demonstrate significantly increased rate of magnetic cell labeling with MPIOs previously incubated with varying amounts of poly‐L ‐lysine, with robust intracellular labeling at 2 hours. Yet the most robust labeling was achieved with the MPIO‐NH₂. Interestingly, even for particle formulations which still had negative zeta potential, enhancement of magnetic cell labeling was achieved. Magn Reson Med, 2011. © 2011 Wiley‐Liss, Inc.     

Assessment of liver function in thioacetamide‐induced rat acute liver injury using an empirical mathematical model and dynamic contrast‐enhanced MRI with Gd‐EOB‐DTPA

Purpose:

To evaluate thioacetamide (TAA)‐induced acute liver injury in rats using an empirical mathematical model (EMM) and dynamic contrast‐enhanced magnetic resonance imaging (DCE‐MRI) with gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid (Gd‐EOB‐DTPA).

Materials and Methods:

Eighteen rats were divided into three groups (normal control [n = 6], TAA [140] [n = 6], and TAA [280] groups [n = 6]). The rats of the TAA (140) and TAA (280) groups were intravenously injected with 140 and 280 mg/kg body weight (BW) of TAA, respectively, while those of the normal control group were intravenously injected with the same volume of saline. DCE‐MRI studies were performed using Gd‐EOB‐DTPA (0.025 mmol Gd/kg; 0.1 mL/kg BW) as the contrast agent 48 hours after TAA or saline injection. After the DCE‐MRI study, blood was sampled and serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) were measured. We calculated the rate of contrast uptake (α), the rate of contrast washout (β), the elimination half‐life of relative enhancement (RE) (T_1/2), the maximum RE (RE_max), and the time to (RE_max) (T_max) from time‐signal intensity curves using EMM.

Results:

The RE_max values in the TAA (140) groups and TAA (280) groups were significantly smaller than that in the normal control group. The T_max value in the TAA (280) group was significantly greater than that in the normal control group. The β value in the TAA (280) group was significantly smaller than those in the normal control and TAA (140) groups, whereas there were no significant differences in β among groups. The T_1/2 value in the TAA (280) group was significantly greater than those in the normal control and TAA (140) groups. The RE_max, T_max, β, and T_1/2 values significantly correlated with AST and ALT.

Conclusion:

The EMM is useful for evaluating TAA‐induced acute liver injury using DCE‐MRI with Gd‐EOB‐DTPA. J. Magn. Reson. Imaging 2012; 36:1483–1489. © 2012 Wiley Periodicals, Inc.     

Myocardial fat quantification in humans: Evaluation by two‐point water‐fat imaging and localized proton spectroscopy

Proton MR spectroscopy (¹H‐MRS) has been used for in vivo quantification of intracellular triglycerides within the sarcolemma. The purpose of this study was to assess whether breath‐hold dual‐echo in‐ and out‐of‐phase MRI at 3.0 T can quantify the fat content of the myocardium. Biases, including T₁, T*₂, and noise, that confound the calculation of the fat fraction were carefully corrected. Thirty‐four of 46 participants had both MRI and MRS data. The fat fractions from MRI showed a strong correlation with fat fractions from MRS (r = 0.78; P < 0.05). The mean myocardial fat fraction for all 34 subjects was 0.7 ± 0.5% (range: 0.11–3%) assessed with MRS and 1.04 ± 0.4% (range: 0.32–2.44%) assessed with in‐ and out‐of‐phase MRI (P < 0.05). Scanning times were less than 15 sec for Dixon imaging, plus an additional minute for the acquisition used for T*₂ calculation, and 15‐20 min for MRS. The average postprocessing time for MRS was 3 min and 5 min for MRI including T*₂ measurement. We conclude that the dual echo method provides a rapid means to detect and quantifying myocardial fat content in vivo. Correction/adjustment for field inhomogeneity using three or more echoes seems crucial for the dual echo approach. Magn Reson Med 63:892–901, 2010. © 2010 Wiley‐Liss, Inc.     

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

Purpose:

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

Materials and Methods:

Ten New Zealand White rabbits were randomized to receive a 6 mL/kg body weight intravenous injection of clinically used iopamidol‐370 (n = 7) or an equivalent amount of 0.9% physiological saline (n = 3). A sequential DW‐MRI was performed to estimate the intrarenal apparent diffusion coefficient (ADC) at 24 h before and 1 h, 24 h, 48 h, and 72 h after administration.

Results:

Iopamidol produced a progressive ADC reduction in inner stripes of the renal outer medulla (IS) by 13.92% (P = 0.05) at 1 h, 17.52% (P = 0.02) at 24 h, 20.23% (P = 0.01) at 48 h and 16.31% (P = 0.04) at 72 h after injection. Cortical ADC was decreased by 14.14% (P = 0.01) at 48 h and 14.12% (P = 0.01) at 72 h after injection. Iopamidol produced slight decrease of ADCs in outer stripes of the outer medulla (OS) and inner medulla (IM) of kidney but without statistical difference. In control group, no significant ADC changes was observed in each anatomic compartment due to saline injection (P > 0.05).

Conclusion:

As demonstrated by DW‐MRI, intravenous iopamidol injection resulted in a successive reduction of intrarenal water diffusion, particularly in IS of kidney. This MR technique may be used as a noninvasive tool to perform a time course study of the pathogenesis associated with contrast‐induced nephropathy (CIN). J. Magn. Reson. Imaging 2012;35:1139‐1144. © 2012 Wiley Periodicals, Inc.     

The effect of maturation on adaptations to strength training and detraining in 11–15‐year‐olds

To investigate how maturity status modifies the effects of strength training and detraining on performance, we subjected 33 young men to 8 weeks of strength training twice per week followed by 8 weeks without training. Changes in performance tests were analyzed in three maturity groups based on years from/to age of predicted peak height velocity (PHV): pre‐PHV (?1.7 ± 0.4 years; n = 10), mid‐PHV (?0.2 ± 0.4 years; n = 11), and post‐PHV (1.0 ± 0.4 years; n = 12). Mean training effects on one repetition maximum strength (3.6–10.0%), maximum explosive power (11–20%), jump length (6.5–7.4%), and sprint times (?2.1% to ?4.7%) ranged from small to large, with generally greater changes in mid‐ and post‐PHV groups. Changes in force–velocity relationships reflected generally greater increases in strength at faster velocities. In the detraining period, the pre‐PHV group showed greatest loss of strength and power, the post‐PHV group showed some loss of sprint performance, but all groups maintained or improved jump length. Strength training was thus generally less effective before the growth spurt. Maintenance programs are needed for most aspects of explosive performance following strength training before the growth spurt and for sprint speed after the growth spurt.     

Comparison of patient‐reported outcomes among those who chose ACL reconstruction or non‐surgical treatment

The aim of our study was to cross‐sectionally compare patient‐reported knee function outcomes between people who chose non‐surgical treatment for ACL injury and those who chose ACL reconstruction. We extracted Knee Injury and Osteoarthritis Outcome Score (KOOS) and EuroQoL‐5D data entered into the Swedish National ACL Registry by patients with a non‐surgically treated ACL injury within 180 days of injury (n = 306), 1 (n = 350), 2 (n = 358), and 5 years (n = 114) after injury. These data were compared cross‐sectionally to data collected pre‐operatively (n = 306) and at 1 (n = 350), 2 (n = 358), and 5 years (n = 114) post‐operatively from age‐ and gender‐matched groups of patients with primary ACL reconstruction. At the 1 and 2 year comparisons, patients who chose surgical treatment reported superior quality of life and function in sports (1 year mean difference 12.4 and 13.2 points, respectively; 2 year mean difference 4.5 and 6.9 points, respectively) compared to those who chose non‐surgical treatment. Patients who chose ACL reconstruction reported superior outcomes for knee symptoms and function, and in knee‐specific and health‐related quality of life, compared to patients who chose non‐surgical treatment.