Age-related changes in the effects of strength training on lower leg muscles in healthy individuals measured using MRI.

BACKGROUND: We previously measured the rate of regaining muscle strength during rehabilitation of lower leg muscles in patients following lower leg casting. Our primary aim in this study was to measure the rate of gain of strength in healthy individuals undergoing a similar training regime. Our secondary aim was to test the ability of MRI to provide a biomarker for muscle function. METHODS: Men and women were recruited in three age groups: 20-30, 50-65 and over 70 years. Their response to resistance training of the right lower leg twice a week for 8 weeks was monitored using a dynamometer and MRI of tibialis anterior, soleus and gastrocnemius muscles at 2 weekly intervals to measure muscle size (anatomical cross-sectional area (ACSA)) and quality (T2 relaxation). Forty-four volunteers completed the study. RESULTS: Baseline strength declined with age. Training had no effect in middle-aged females or in elderly men in dorsiflexion. Other groups significantly increased both plantarflexion and dorsiflexion strength at rates up to 5.5 N m week-1 in young females in plantarflexion and 1.25 N m week-1 in young males in dorsiflexion. No changes were observed in ACSA or T2 in any age group in any muscle. CONCLUSION: Exercise training improves muscle strength in males at all ages except the elderly in dorsiflexion. Responses in females were less clear with variation across age and muscle groups. These results were not reflected in simple MRI measures that do not, therefore, provide a good biomarker for muscle atrophy or the efficacy of rehabilitation.

MRI and the distribution of bone marrow fat in hip osteoarthritis.

PURPOSE: To characterize the distribution of bone marrow fat in hip osteoarthritis (OA) using magnetic resonance imaging (MRI) and to assess its use as a potential biomarker. MATERIALS AND METHODS: In all, 67 subjects (39 female, 28 male) with either total hip replacement (THA) or different severities of radiographic OA, assessed by Kellgren-Lawrence grading (KLG), underwent 3T MRI of the pelvis using the IDEAL sequence to separate fat and water signals. Six regions of interest (ROIs) were identified within the proximal femur. Within each ROI the fractional-fat distribution, represented by pixel intensities, was described by its mean, standard deviation, skewness, kurtosis, and entropy. RESULTS: Hips were graded: 12 as severe symptomatic (THA), 33 had KLG0 or 1, 9 were KLG2, 11 with KLG3, and 2 with KLG4 were analyzed together. The fractional-fat content in the whole proximal femur did not vary with severity in males (mean (SD) 91.2 (6.0)%) but reduced with severity in females from 89.1 (6.7)% (KLG0,1), 91.5 (2.9)% (KLG2), 85.8 (16.7)% (KLG3,4) to 77.5 (11.9)% (THA) (analysis of variance [ANOVA] P = 0.029). These differences were most pronounced in the femoral head, where mean values fell with OA severity in both sexes from 97.9% (2.5%) (KLG0,1) to 73.0% (25.9%) (THA, P < 0.001) with the largest difference at the final stage. The standard deviation and the entropy of the distribution both increased (P < 0.001). CONCLUSION: Descriptors of the fractional fat distribution varied little with the severity of OA until the most severe stage, when changes appeared mainly in the femoral head, and have, therefore, limited value as biomarkers. LEVEL OF EVIDENCE: 2 J. Magn. Reson. Imaging 2017;45:42-50.

T1 mapping for assessment of myocardial injury and microvascular obstruction at one week post myocardial infarction.

OBJECTIVES: To compare 3T T1 mapping to conventional T2-weighted (T2W) imaging for delineating myocardial oedema one week after ST-elevation myocardial infarction (STEMI), and to explore the confounding effects of microvascular obstruction (MVO) on each technique. METHODS: T2W spectral attenuated inversion recovery and native T1 mapping were applied in 10 healthy volunteers and 62 STEMI patients, and late gadolinium enhancement was included for infarct localisation at 1 week and at 6 months post-STEMI. Segmental T1 values and T2W signal intensity ratios were calculated; oedema volumes and salvage indices were determined in patients using image thresholding-a receiver operator characteristic (ROC) derived T1 threshold, and a 2SD T2W threshold; and the results were compared between patients with/without MVO (n=35/27). RESULTS: Native T1 mapping delineated oedema with significantly better discriminatory power than T2W-as indicated by ROC analysis (area-under-the-curve, AUC=0.89 versus 0.83, p=0.009; and sensitivity/specificity=83/83% versus 73/73%). The optimal ROC threshold derived for T1 mapping was 1241ms, which gave significantly larger oedema volumes than 2SD T2W (p=0.006); with this threshold, patients with and without MVO showed similar oedema volumes, but patients with MVO had significantly poorer salvage indices (p<0.05) than those without. Neither method was significantly affected by MVO, the volume of which was seen to increase exponentially with infarct size. CONCLUSIONS: Native T1 mapping at 3T can delineate oedema one week post-STEMI, showing larger oedema volumes and better discriminatory power than T2W imaging, and it is suitable for quantitative thresholding. Both techniques are robust against MVO-related magnetic susceptibility.

Selection of magnetization catalyzation and readout methods for modified Look-Locker inversion recovery: a T1 mapping primer.

BACKGROUND: The purpose of this work was to evaluate different magnetization preparation and readout sequences for modified Look-Locker inversion recovery (MOLLI) toward improved T1 mapping in the heart. Elements investigated include: catalyzation sequences to prepare the magnetization before readout, alternate k-space trajectories, a spoiled gradient recalled echo readout, and a 5b(3b)3b MOLLI sampling scheme ('b' denoting beats). METHODS: Conventional 3b(3b)3b(3b)5b MOLLI with a linear k-space trajectory was compared to four variants in simulations, in vitro and in vivo (at 3T). Variants were centric conventional MOLLI, centric-paired conventional MOLLI, linear 5b(3b)3b MOLLI and spoiled gradient recalled echo MOLLI. Each of these was applied with three magnetization catalyzation methods, and T1 measurement accuracy and precision were evaluated in simulations via a Monte Carlo algorithm, in a set of calibrated phantoms, and in ten healthy volunteers. Contrast-to-noise, heart rate dependence and B1+ dependence were also evaluated. RESULTS: A linear k-space trajectory was superior in vitro to centric and centric-paired trajectories. Of the catalyzation methods, preparation of transverse magnetization only-using a linearly increasing flip angle catalyzation-improved MOLLI T1 measurement accuracy, precision, and map quality versus methods that include catalyzation of the longitudinal magnetization. The 5b(3b)3b MOLLI scheme offered comparable native T1 measurement accuracy and precision to conventional MOLLI, despite its shortened acquisition. CONCLUSIONS: MOLLI T1 measurement accuracy, precision, and map quality depend on the method of catalyzation of magnetization prior to image acquisition, as well as on the readout method and MOLLI sampling scheme used.

Low-dose dobutamine adds incremental value to late gadolinium enhancement cardiac magnetic resonance in the prediction of adverse remodelling following acute myocardial infarction.

AIMS: To examine the relative and combined value of late gadolinium enhancement (LGE) and low-dose dobutamine (LDD) cardiac magnetic resonance (CMR) to predict 'adverse remodelling' (AR) following acute myocardial infarction (AMI). METHODS AND RESULTS: Forty-five patients with AMI were recruited. CMR was performed 2-4 days after presentation and at 6 months. Ventricular wall motion and volume were recorded at rest and following dobutamine infusion. Measures of first pass perfusion, persistent microvascular obstruction (PMO), and LGE were obtained following contrast administration. Quantitation was performed using the MEDIS 6.2 software. Regression analysis was employed to determine the univariables and multivariate models most predictive of AR at 6 months. The incremental and relative value of LDD over LGE was investigated. The most predictive univariable was 'volume of PMO' (r = 0.51, r2 = 0.26, P < 0.001). The optimal 'combined' multivariate model, utilizing data from all components, was highly predictive of AR (r = 0.82, r2 = 0.67, P < 0.001). The optimal model using parameters only from the LGE component also predicted remodelling (r = 0.65, r2 = 42.0, P = 0.001) but with less accuracy. In contrast, the optimal model using variables from the LDD component alone predicted remodelling with a similar accuracy to the optimal combined model (r = 0.82, r2 = 0.67, P < 0.001). CONCLUSION: A comprehensive CMR examination accurately predicts AR following AMI. LDD is superior to LGE CMR in this respect. These data suggest that LDD not only adds incremental value to LGE in the prediction of remodelling post-AMI but also may be utilized alone with the same predictive power.

In vivo proton magnetic resonance spectroscopy of breast cancer: a review of the literature.

An emerging clinical modality called proton magnetic resonance spectroscopy ((1)H-MRS) enables the non-invasive in vivo assessment of tissue metabolism and is demonstrating applications in improving the specificity of MR breast lesion diagnosis and monitoring tumour responsiveness to neoadjuvant chemotherapies. Variations in the concentration of choline-based cellular metabolites, detectable with (1)H-MRS, have shown an association with malignant transformation of tissue in in vivo and in vitro studies. (1)H-MRS exists as an adjunct to the current routine clinical breast MR examination. This review serves as an introduction to the field of breast (1)H-MRS, discusses modern high-field strength and quantitative approaches and technical considerations, and reviews the literature with respect to the application of (1)H-MRS for breast cancer.

Quantification techniques to minimize the effects of native T1 variation and B1 inhomogeneity in dynamic contrast-enhanced MRI of the breast at 3 T.

The variation of the native T(1) (T(10)) of different tissues and B(1) transmission-field inhomogeneity at 3 T are major contributors of errors in the quantification of breast dynamic contrast-enhanced MRI. To address these issues, we have introduced new enhancement indices derived from saturation-recovery snapshot-FLASH (SRSF) images. The stability of the new indices, i.e., the SRSF enhancement factor (EF(SRSF)) and its simplified version (EF'(SRSF)) with respect to differences in T(10) and B(1) inhomogeneity was compared against a typical index used in breast dynamic contrast-enhanced MRI, i.e., the enhancement ratio (ER), by using computer simulations. Imaging experiments with Gd-DTPA-doped gel phantoms and a female volunteer were also performed. A lower error was observed in the new indices compared to enhancement ratio in the presence of typical T(10) variation and B(1) inhomogeneity. At changes of relaxation rate (ΔR(1)) of 8 s(-1), the differences between a T(10) of 1266 and 566 ms are <1, 12, and 58%, respectively, for EF(SRSF), EF'(SRSF), and ER, whereas differences of 20, 8, and 51%, respectively, result from a 50% B(1) field reduction at the same ΔR(1). These quantification techniques may be a solution to minimize the effect of T(10) variation and B(1) inhomogeneity on dynamic contrast-enhanced MRI of the breast at 3 T.

A longitudinal MRI study of muscle atrophy during lower leg immobilization following ankle fracture.

PURPOSE: To investigate MRI biomarkers of muscle atrophy during cast immobilization of the lower leg. MATERIALS AND METHODS: Eighteen patients (8 male, 10 female), who had one lower leg immobilized in a cast, underwent 3.0 Tesla (T) MR imaging 5, 8, 15, 29, and 43 days after casting. Measurements were made on both lower legs of total muscle volume. Cross-sectional area (CSA), fractional water content, and T(2) were measured in tibialis anterior (TA), gastrocnemius medialis (GM) and lateralis (GL) and soleus (SOL). Fiber pennation angle was measured in GM. RESULTS: Total muscle volume decreased by 17% (P < 0.001) over the 6 weeks of immobilization. The greatest loss in CSA (mean[SD]) was seen in GM (-23.3(8.7)%), followed by SOL (-19.0(9.8)%), GL (-17.1(6.5)%), and TA (-10.7(5.9)%). Significant reductions of CSA were also detectable in the contra-lateral leg. T(2) increased in all muscles: TA 27.0(2.5) ms to 29.6(2.8) ms (P < 0.001), GM 34.6(2.9) ms to 39.8(5.4) ms (P < 0.001) and SOL 34.4 (2.9) ms to 44.9(5.9) ms (P < 0.001). Small reductions were found in fractional water content. Pennation angle decreased in the cast leg (P < 0.001). CONCLUSION: Quantitative MR imaging can detect and monitor progressive biochemical and biophysical changes in muscle during immobilization.

Changes in foetal liver T2* measurements by MRI in response to maternal oxygen breathing: application to diagnosing foetal growth restriction.

The motivation of the project was to investigate the use of oxygen-challenge magnetic resonance imaging (OC-MRI) as a method of diagnosing foetal growth restriction. Foetal growth restriction is associated with restricted foetal oxygen supply and is also associated with increased risks of perinatal mortality and morbidity, and a number of serious and chronic health problems. Measurements of T2* relaxation time, an MRI parameter which increases with blood oxygenation, were made in the right lobe of the foetal liver in 80 singleton pregnancies, before and after the mother breathed oxygen. The groups consisted of 41 foetuses with normal growth and 39 with apparent growth restriction. The mean +/- SD gestational age at scanning was 35 +/- 3 weeks. Changes in foetal liver T2* on maternal oxygen breathing showed no significant difference between the groups therefore the OC-MRI protocol used in this study has no value in the diagnosis of foetal growth restriction. A secondary finding was that a significant positive correlation of T2* change with gestational age was observed. Future studies on the use of oxygen-challenge MRI to investigate foetal growth restriction may therefore need to control for gestational age at the time of MR scanning in order to observe any underlying foetal growth-related effects.

B1 transmission-field inhomogeneity and enhancement ratio errors in dynamic contrast-enhanced MRI (DCE-MRI) of the breast at 3T.

PURPOSE: To quantify B(1) transmission-field inhomogeneity in breast imaging of normal volunteers at 3T using 3D T(1)-weighted spoiled gradient echo and to assess the resulting errors in enhancement ratio (ER) measured in dynamic contrast-enhanced MRI (DCE-MRI) studies of the breast. MATERIALS AND METHODS: A total of 25 volunteers underwent breast imaging at 3T and the B(1) transmission-fields were mapped. Gel phantoms that simulate pre- and postcontrast breast tissue T(1) were developed. The effects of B(1)-field inhomogeneity on ER, as measured using a 3D spoiled gradient echo sequence, were investigated by computer simulation and experiments on gel phantoms. RESULTS: It was observed that by using the patient orientation and MR scanner employed in this study, the B(1) transmission-field field is always reduced toward the volunteer's right side. The median B(1)-field in the right breast is reduced around 40% of the expected B(1)-field. For some volunteers the amplitude was reduced by more than 50%. Computer simulation and experiment showed that a reduction in B(1)-field decreases ER. This reduction increases with both B(1)-field error and contrast agent uptake. CONCLUSION: B(1) transmission-field inhomogeneity is a critical issue in breast imaging at 3T and causes errors in quantifying ER. These errors would be sufficient to reduce the conspicuity of a malignant lesion and could result in reduced sensitivity for cancer detection.

The relationship between transmural extent of infarction on contrast enhanced magnetic resonance imaging and recovery of contractile function in patients with first myocardial infarction treated with thrombolysis.

BACKGROUND: The aim of the current study was to assess the utility of transmurality of delayed enhancement on cardiac magnetic resonance imaging (MRI) in predicting functional recovery in patients with first ST-elevation myocardial infarction (MI) who had received thrombolysis. METHODS: Nineteen patients underwent cine and contrast-enhanced MRI 3 days and 8 weeks after MI. The transmural extent of infarction (TEI) was determined from the late enhancement component of the first scan. Segmental wall thickening was scored from the cine components of both the initial and follow-up scans. RESULTS: The TEI was inversely related to the likelihood of improvement in wall thickening; chi(2) test for trend = 53.9, p < 0.0001. Delayed enhancement with >50% transmurality predicted a lack of recovery with 82% sensitivity and 54% specificity. The equivalent values for >75% transmurality were 57 and 77%, respectively. The proportion of the left ventricular segments exhibiting functional recovery was related to the percentage of the left ventricle that was severely dysfunctional but had

The relationship between vascular and metabolic characteristics of primary breast tumours.

The objective of this study was to investigate the relationship between vascular and metabolic characteristics of breast tumours in vivo, using contrast-enhanced dynamic MRI and 2-[(18)F] fluoro-2-deoxy- d-glucose (FDG) PET imaging. Twenty patients with large or locally advanced primary breast cancers were imaged prior to therapy. MRI data were acquired using a dynamic gradient echo sequence and analysed using two pharmacokinetic models. Static PET data were acquired in 2D mode. A significant association ( P<0.05) was observed between the calculated exchange rate constants of both pharmacokinetic models and calculated PET FDG dose uptake ratios (DUR). Statistical analysis showed that the exchange rate constants can explain between 27 and 44% of the variance observed in the PET FDG uptake ratios. A relationship was demonstrated between the vascular and metabolic characteristics of primary breast tumours showing that any assessment of tumour metabolic activity using PET may be controlled at least in part by delivery of uptake agent due to the vascular characteristics of the tumour. MRI and PET provide methods of assessing breast tumour vascularity and metabolism in vivo using the exchange rate constants of dynamic MRI, and DUR of PET, respectively, these measures being related but not equivalent.

Brain activation and the phonological loop: the impact of rehearsal.

Brain activation studies offer valuable techniques for exploring human cognition to complement behavioral measures and several studies report a wide range of neuroanatomical networks activated during verbal immediate memory. Behavioral investigations have shown use of multiple cognitive strategies across and within individuals, although aggregate data appear to reflect a common cognitive function. Variation in cognitive strategies could result in aggregate activation patterns that are relatively widespread and difficult to interpret. Imaging data (fMRI) from six participants instructed to use subvocal rehearsal showed significant left hemisphere activation in the inferior parietal gyrus and inferior and middle frontal gyri, a pattern of activation more clearly focused than in previous brain activation studies of immediate verbal serial ordered recall. Our results should be relatively free of the influence of other mental operations, and emphasise the importance of considering which cognitive strategies might give rise to focused or to diverse patterns of brain activation.

Advanced imaging: Magnetic resonance imaging in implant dentistry.

For accurate and safe placement of dental implants, and planning of associated surgery, a full assessment of the surgical anatomy of the site is necessary. Thus, it is highly desirable to have tomographic, sectional information available, to permit the implant to be aligned correctly. In recent years, X-ray computed tomography (CT) has become accepted as the gold standard in assessment, but the exposure to ionising radiation can be substantial. Artefacts due to dental restorations can also be significant, and some doubts may exist over the accuracy of reformatted CT. Magnetic resonance imaging (MRI) entails no exposure to ionising radiation, and allows direct acquisition of tomographic information in any desired plane. Sequential studies may be safely performed, allowing us a valuable insight into bone graft behaviour. Other than in a small number of cases, MRI may be safely used for presurgical assessments. Artefacts are few and in most cases localised. The surgical confidence from the sectional information gained is a significant step forward in the safe placement of dental implants.