Detection of Focal Longitudinal Changes in the Brain by Subtraction of MR Images.

BACKGROUND AND PURPOSE: The detection of new subtle brain pathology on MR imaging is a time-consuming and error-prone task for the radiologist. This article introduces and evaluates an image-registration and subtraction method for highlighting small changes in the brain with a view to minimizing the risk of missed pathology and reducing fatigue. MATERIALS AND METHODS: We present a fully automated algorithm for highlighting subtle changes between multiple serially acquired brain MR images with a novel approach to registration and MR imaging bias field correction. The method was evaluated for the detection of new lesions in 77 patients undergoing cardiac surgery, by using pairs of fluid-attenuated inversion recovery MR images acquired 1-2 weeks before the operation and 6-8 weeks postoperatively. Three radiologists reviewed the images. RESULTS: On the basis of qualitative comparison of pre- and postsurgery FLAIR images, radiologists identified 37 new ischemic lesions in 22 patients. When these images were accompanied by a subtraction image, 46 new ischemic lesions were identified in 26 patients. After we accounted for interpatient and interradiologist variability using a multilevel statistical model, the likelihood of detecting a lesion was 2.59 (95% CI, 1.18-5.67) times greater when aided by the subtraction algorithm (P = .017). Radiologists also reviewed the images significantly faster (P < .001) by using the subtraction image (mean, 42 seconds; 95% CI, 29-60 seconds) than through qualitative assessment alone (mean, 66 seconds; 95% CI, 46-96 seconds). CONCLUSIONS: Use of this new subtraction algorithm would result in considerable savings in the time required to review images and in improved sensitivity to subtle focal pathology.

A Semiautomatic Method for Multiple Sclerosis Lesion Segmentation on Dual-Echo MR Imaging: Application in a Multicenter Context.

BACKGROUND AND PURPOSE: The automatic segmentation of MS lesions could reduce time required for image processing together with inter- and intraoperator variability for research and clinical trials. A multicenter validation of a proposed semiautomatic method for hyperintense MS lesion segmentation on dual-echo MR imaging is presented. MATERIALS AND METHODS: The classification technique used is based on a region-growing approach starting from manual lesion identification by an expert observer with a final segmentation-refinement step. The method was validated in a cohort of 52 patients with relapsing-remitting MS, with dual-echo images acquired in 6 different European centers. RESULTS: We found a mathematic expression that made the optimization of the method independent of the need for a training dataset. The automatic segmentation was in good agreement with the manual segmentation (dice similarity coefficient = 0.62 and root mean square error = 2 mL). Assessment of the segmentation errors showed no significant differences in algorithm performance between the different MR scanner manufacturers (P > .05). CONCLUSIONS: The method proved to be robust, and no center-specific training of the algorithm was required, offering the possibility for application in a clinical setting. Adoption of the method should lead to improved reliability and less operator time required for image analysis in research and clinical trials in MS.

Is Abdominal Fat Distribution Measured by Axial CT Imaging an Indicator of Complications and Mortality in Acute Pancreatitis?

BACKGROUND: Obesity is an important risk-stratifying co-morbidity for many pathological conditions. Controversy exists about its influence in outcomes after acute pancreatitis (AP). This study assessed abdominal fat distribution (subcutaneous, retroperitoneal and intra-abdominal) measured using computer tomography (CT) images and related it to outcomes in patients with AP. METHODS: The case notes of patients admitted with AP were identified from computerised records from 2008 to the 2013. Image analysis software was used to assess the individual abdominal fat distributions from CT images. RESULTS: A total of 79 patients were included. There was no relationship between fat distribution and either severity of, or mortality from, AP. Fat distribution was not found to be an independent risk factor on multivariate analysis. There was, however, a positive correlation between retroperitoneal and intra-abdominal fat with APACHE II scores, Ranson and Glasgow score and Multiple Organ Dysfunction score (MODS) on various days following admission (r = 0.421, p = 0.0008; r = 0.469, p < 0.0001; r = 0.398, p = 0.007; r = 0.336, p = 0.011, respectively). On multiple logistical regression analysis, the only variables associated with mortality were Balthazar Severity Index, MODS and EWS with a p value of <0.0001, 0.0019 and 0.0481, respectively. CONCLUSIONS: Obese patients have worse predicted outcomes as measured by the EWS, MODS and Ranson scores. Abdominal fat distribution, however, was not shown to be directly related to AP severity or mortality. The addition of fat parameters may be of use in prognostic CT severity index models, but from this data, it does not appear to be an independent risk factor of adverse outcome.

A Novel Ultrasound-Based Carotid Plaque Risk Index Associated with the Presence of Cerebrovascular Symptoms.

PURPOSE: The purpose of this study was to determine the efficacy of a novel ultrasound-based carotid plaque risk index (CPRI) in predicting the presence of cerebrovascular symptoms in patients with carotid artery stenosis. MATERIALS AND METHODS: This was a cross-sectional, observational study involving 56 patients (mean age 76.6 years, 62.5 % male). Plaque grayscale median (GSM) and surface irregularity indices (SII) were measured in 82 stenosed carotid arteries (range 10 - 95 %) and combined with the degree of stenosis (DOS) in the form of (DOS*SII)/(1 + GSM). A reduced index DOS/(1 + GSM) not incorporating plaque surface irregularities was also investigated. Receiver operating characteristic curves (ROC) were used to study the diagnostic efficacy of CPRI, comparing against DOS and an equivalent risk index constructed using a conventional logistic regression based method with model parameters optimized to the dataset (CPRIlogistic). RESULTS: There were 42 stenosed carotid arteries with cerebrovascular symptoms, and 40 without symptoms. The presence of symptoms significantly correlated with DOS, GSM and SII (p < 0.01). The median CPRI of the symptomatic (asymptomatic) groups were 23.2 (9.2) compared with 0.71 (0.30) for CPRIlogistic (p < 0.01). The diagnostic performance of CPRI exceeded that of CPRIlogistic and DOS, and demonstrated a better separation of the symptomatic and asymptomatic groups. CONCLUSION: Our novel risk index combines quantitative measures of carotid plaque echogenicity and surface irregularities with the degree of stenosis. It is a better predictor of cerebrovascular symptoms than the degree of stenosis and could be valuable in studies and clinical trials aimed at identifying vulnerable carotid artery stenoses.

Recommendations to improve imaging and analysis of brain lesion load and atrophy in longitudinal studies of multiple sclerosis.

Focal lesions and brain atrophy are the most extensively studied aspects of multiple sclerosis (MS), but the image acquisition and analysis techniques used can be further improved, especially those for studying within-patient changes of lesion load and atrophy longitudinally. Improved accuracy and sensitivity will reduce the numbers of patients required to detect a given treatment effect in a trial, and ultimately, will allow reliable characterization of individual patients for personalized treatment. Based on open issues in the field of MS research, and the current state of the art in magnetic resonance image analysis methods for assessing brain lesion load and atrophy, this paper makes recommendations to improve these measures for longitudinal studies of MS. Briefly, they are (1) images should be acquired using 3D pulse sequences, with near-isotropic spatial resolution and multiple image contrasts to allow more comprehensive analyses of lesion load and atrophy, across timepoints. Image artifacts need special attention given their effects on image analysis results. (2) Automated image segmentation methods integrating the assessment of lesion load and atrophy are desirable. (3) A standard dataset with benchmark results should be set up to facilitate development, calibration, and objective evaluation of image analysis methods for MS.

Microstructural magnetic resonance imaging of cortical lesions in multiple sclerosis.

BACKGROUND: Pathologic and magnetic resonance imaging (MRI) studies have shown that cortical lesions (CLs) are a frequent finding in multiple sclerosis (MS). OBJECTIVE: To quantify microstructural damage in CLs and normal appearing (NA) cortex in relapse-onset MS patients at different stages of the disease. METHODS: Brain double inversion recovery (DIR), diffusion tensor (DT) MRI and 3D T 1-weighted scans were acquired from 35 relapsing-remitting (RR) patients, 23 secondary progressive (SP) patients, 12 benign (B) MS patients and 41 healthy controls (HC). Diffusivity values in CLs, cortex, white matter (WM) lesions and normal-appearing white matter (NAWM) were assessed. RESULTS: Compared to HC, MS patients had a significantly lower fractional anisotropy (FA) and higher mean diffusivity (MD) in the cortex and NAWM. CLs had higher FA vs HC cortex and vs patients' cortex. Compared to RRMS patients, SPMS patients had higher WM lesion volume, higher MD in the cortex, and more severe damage to the NAWM and WM lesions. Compared to SPMS patients, BMS patients had lower MD and FA of CLs. Damage in other compartments was similar between SPMS and BMS patients. Damage in CLs had a high power to discriminate BMS from SPMS (area under the curve: 79-91%), with high specificity (85%), sensitivity (100%) and accuracy (90%). CONCLUSIONS: Microstructural imaging features of CLs differ from those of WM lesions and are likely to reflect neuronal damage and microglial activation. The nature and extent of CL damage can be used to help distinguish the different MS clinical phenotypes.

Spatial normalization and regional assessment of cord atrophy: voxel-based analysis of cervical cord 3D T1-weighted images.

BACKGROUND AND PURPOSE: VBM is widely applied to characterize regional differences in brain volume among groups of subjects. The aim of this study was to develop and validate a method for voxelwise statistical analysis of cord volume and to test, with this method, the correlation between cord tissue loss and aging. MATERIALS AND METHODS: 3D T1-weighted scans of the spinal cord were acquired from 90 healthy subjects spanning several decades of life. Using an AS method, we outlined the cord surface and created output images reformatted with image planes perpendicular to the estimated cord centerline. Unfolded cervical cord images were coregistered into a common standard space, and smoothed cord binary masks, produced by using the cord outlines estimated by the AS approach, were used as input images for spatial statistics. RESULTS: High spatial correlation between normalized images was observed. Averaging of the normalized scans allowed the creation of a cervical cord template and of a standardized region-of-interest atlas. VBM analysis showed some significant associations between a decreased probability of cord tissue and aging. Results were robust across different smoothing levels, but the use of an anisotropic Gaussian kernel gave the optimal trade-off between spatial resolution and the requirements of the Gaussian random field theory. CONCLUSIONS: VBM analysis of the cervical cord was feasible and holds great promise for accurate localization of regional cord atrophy in several neurologic conditions.

Imaging vascular function for early stage clinical trials using dynamic contrast-enhanced magnetic resonance imaging.

Many therapeutic approaches to cancer affect the tumour vasculature, either indirectly or as a direct target. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) has become an important means of investigating this action, both pre-clinically and in early stage clinical trials. For such trials, it is essential that the measurement process (i.e. image acquisition and analysis) can be performed effectively and with consistency among contributing centres. As the technique continues to develop in order to provide potential improvements in sensitivity and physiological relevance, there is considerable scope for between-centre variation in techniques. A workshop was convened by the Imaging Committee of the Experimental Cancer Medicine Centres (ECMC) to review the current status of DCE-MRI and to provide recommendations on how the technique can best be used for early stage trials. This review and the consequent recommendations are summarised here. Key Points • Tumour vascular function is key to tumour development and treatment • Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) can assess tumour vascular function • Thus DCE-MRI with pharmacokinetic models can assess novel treatments • Many recent developments are advancing the accuracy of and information from DCE-MRI • Establishing common methodology across multiple centres is challenging and requires accepted guidelines.

Diffusion tensor MRI tractography and cognitive impairment in multiple sclerosis.

OBJECTIVE: To assess the correlation between cognitive impairment and overall vs regional CNS damage, quantified using conventional and diffusion tensor (DT) MRI tractography in multiple sclerosis (MS). METHODS: Brain dual-echo, T1-weighted, and DT MRI data were acquired from 82 patients with MS. DT tractography was used to produce maps of white matter (WM) tracts involved in cognition. The sensory thalamocortical projections and optic radiations were studied as "control" WM tracts. The contribution of global brain damage (T2 lesion volume, normalized brain volume, gray matter [GM] volume, WM volume, DT MRI measures of normal-appearing WM and GM damage) and damage to selected WM tracts to overall cognitive impairment and to impairment at individual neuropsychological tests was assessed using a random forest (RF) analysis. RESULTS: Thirty-three patients had cognitive impairment. The majority of MRI measures differed significantly between cognitively impaired and cognitively preserved (CP) patients. Significant correlations were found between performance in the majority of neuropsychological tests and global or regional brain damage (r ranging from -0.60 to 0.57). The RF analysis showed a high performance in classifying cognitively impaired vs CP patients, with a classification (C)-index = 76.8, as well as in classifying patients' impairment in individual neuropsychological tests (C-index between 75.6% and 86.6%). Measures of lesional damage in cognitive-related tracts, rather than measures of normal-appearing WM damage in the same tracts or global brain/WM/GM damage, resulted in the highest classification accuracy. CONCLUSIONS: Lesions in strategic brain WM tracts contribute to cognitive impairment in MS through a multisystem disconnection syndrome.

A multicenter assessment of cervical cord atrophy among MS clinical phenotypes.

OBJECTIVE: In this multicenter study, a new semiautomatic method for segmenting the cervical cord from C2 to C5 was used to investigate the correlation between cord atrophy and clinical disability in a large sample of patients with multiple sclerosis (MS). METHODS: T2 and 3-dimensional T1-weighted cervical cord scans and dual-echo brain scans were acquired from 143 healthy controls, 22 patients with clinically isolated syndromes (CIS), 101 patients with relapsing-remitting MS (RRMS), 79 patients with secondary progressive MS (SPMS), 58 patients with benign MS (BMS), and 75 patients with primary progressive MS (PPMS) in 3 European centers. Normalized cervical cord cross-sectional area (CSAn) was measured by an active surface cord model. Between-group comparisons were performed using linear mixed-effect models. A nonparametric kernel estimator was used to obtain smoothed plots of CSA along the cervical cord. RESULTS: Cord CSAn was significantly lower in PPMS vs healthy controls, BMS vs RRMS, SPMS vs BMS, and RRMS. From C2 to C5, a net separation and definition of the plots of patients with BMS, PPMS, and SPMS was seen with respect to those of the other study groups. CSAn was correlated with Expanded Disability Status Scale (r = -0.49, p < 0.0001), with a differential effect among disease clinical phenotypes: no association in either CIS or in BMS; association in RRMS (r = -0.30, p = 0.001), SPMS (r = -0.34, p = 0.001), and PPMS (r = -0.27, p = 0.01). CONCLUSIONS: Cervical cord atrophy provides a relevant and useful marker for the characterization of clinical heterogeneity of patients with MS. The stability of this measure among different centers supports its use as potential outcome measure to monitor disease progression in multicenter trials.

Diffusion MR imaging in multiple sclerosis: technical aspects and challenges.

SUMMARY: Diffusion tensor (DT) MR imaging has frequently been applied in multiple sclerosis (MS) because of its ability to detect and quantify disease-related changes of the tissue microstructure within and outside T2-visible lesions. DT MR imaging data collection places high demands on scanner hardware and, though the acquisition and postprocessing can be relatively straightforward, numerous challenges remain in improving the reproducibility of this technique. Although there are some issues concerning image quality, echo-planar imaging is the most widely used acquisition scheme for diffusion imaging studies. Once the DT is estimated, indexes conveying the size, shape, and orientation of the DT can be calculated and further analyzed by using either histogram- or region-of-interest-based analyses. Because the orientation of the DT reflects the orientation of the axonal fibers of the brain, the pathways of the major white matter tracts can also be visualized. The DT model of diffusion, however, is not sufficient to characterize the diffusion properties of the brain when complex populations of fibers are present in a single voxel, and new ways to address this issue have been proposed. Two developments have enabled considerable improvements in the application of DT MR imaging: high magnetic field strengths and multicoil receiver arrays with parallel imaging. This review critically discusses models, acquisition, and postprocessing approaches that are currently available for DT MR imaging, as well as their limitations and possible improvements, to provide a better understanding of the strengths and weaknesses of this technique and a background for designing diffusion studies in MS.

A simple, reproducible method for monitoring the treatment of tumours using dynamic contrast-enhanced MR imaging.

Dynamic contrast-enhanced MR imaging (DCE-MRI) may act as a biomarker for successful cancer therapy. Simple, reproducible techniques may widen this application. This paper demonstrates a single slice imaging technique. The image acquisition is performed in less than 500 ms making it relatively insensitive to respiratory motion. Data from phantom studies and a reproducibility study in solid human tumours are presented. The reproducibility study showed a coefficient of variation (CoV) of 19.1% for K(trans) and 15.8% for the initial area under the contrast enhancement curve (IAUC). This was improved to 16 and 13.9% if tumours of diameter less than 3 cm were excluded. The individual repeatability (the range within which individual measurements are expected to fall) was 30.6% for K(trans) and 26.5% for IAUC for tumours greater than 3 cm diameter. This approach to DCE-MRI image acquisition can be performed with standard clinical scanners, and data analysis is straightforward. For treatment trials with 10 patients in a cohort, the CoV implies that the method would be sensitive to a treatment effect of greater than 18%. The individual repeatability is well inside the 40% change shown to be important in clinical studies using this DCE-MRI technique.

A method for obtaining tract-specific diffusion tensor MRI measurements in the presence of disease: application to patients with clinically isolated syndromes suggestive of multiple sclerosis.

The aim of this study was to investigate whether neurological symptoms related to a specific axonal fiber tract in brain white matter were associated with a higher degree of tissue damage in that region, in patients at presentation with clinically isolated syndromes (CIS) suggestive of multiple sclerosis. To this end, a magnetic resonance imaging (MRI) method to segment and evaluate the fiber bundle of interest was implemented, taking care to circumvent the problems caused by pathology. Diffusion tensor (DT) MRI tractography was used to construct, from healthy volunteer data, a probability map for the pyramidal tract (PYT), and this map was applied to patients to calculate DT-derived metrics inside the PYT. In CIS patients with clinical symptoms related to motor function, the DT-derived mean diffusivity and the lesion volume in the PYT were found to be increased, while the fractional anisotropy was no different, when compared to those patients without motor symptoms. These results may be explained by several microstructural changes in the damaged tissue, such as changes in the permeability of axonal cell membranes, decreases of axonal density and edema. The approach taken to analyze a specific fiber tract was possible because the axons in the tract have a high orientational coherence, allowing tissue structure changes to be isolated from the tissue architecture. Its extension to other white matter fiber bundles is therefore limited to bundles with high orientational coherence.

A comparison of polyacrylamide gels and radiochromic film for source measurements in intravascular brachytherapy.

For intravascular brachytherapy with catheter-based systems, AAPM Task Group 60 has recommended measurements that should be made to characterize the sources. Beta emitters, including (90)Sr/(90)Y are ideal for intravascular brachytherapy, but problems arise in measuring dose distributions in the high dose gradient region at short distances from the source. In this paper, measurements of radial and orthogonal dose distributions and dose profiles for a (90)Sr/(90)Y source train using polyacrylamide gel (PAG) dosimetry and a high-field 4.7 Tesla MRI scanner are presented and compared with measurements made with two types of radiochromic film, MD-55 and HD-810. For the PAG system, the dose distributions were determined with in-plane resolutions of 0.4 mm and 0.2 mm. The measurements of absorbed dose distributions both orthogonal and parallel to the source axis show good agreement between the PAG and radiochromic film. The absolute dose at a radial distance of 2 mm in the central 32 mm of a line parallel to the axis was measured. For the PAG the measured absorbed dose was 1.25% lower, for MD-55 4% higher and for the HD-810 1.6% higher when compared with the value given by the source calibration. These results confirm that both absorbed dose and dose distributions for high gradient vascular brachytherapy sources can be measured using PAG but the disadvantages of gel manufacture and the need for access to a high resolution scanner suggests that the use of radiochromic film is the method of choice.

Whole-brain atrophy in multiple sclerosis measured by two segmentation processes from various MRI sequences.

Recent MRI and pathologic studies have drawn attention to the destructive nature of the multiple sclerosis (MS) disease process, including the early occurrence of axonal and neuronal loss, leading to macroscopic brain and spinal cord atrophy. Measurement of brain atrophy from MRI has emerged as a potential outcome measure and marker of disease severity in MS and neurodegenerative diseases such as Alzheimer's. However, the optimal method for quantifying atrophy has not been established, including the choice of pulse sequence and segmentation algorithm employed. Using two different MRI scanners to ensure generalizability of results, we compared the reproducibility of four pulse sequences and two analysis methods (fully automated [FA] and semi-automated [SA]) when obtaining brain parenchymal fraction (BPF), a normalized measure of whole-brain atrophy, in patients with MS (n=13) and normal controls (n=2). In order to ensure the validity of our fully automated analysis technique, we also used it to evaluate the atrophy rate over nine months in 57 MS patients from the placebo arm of a clinical trial. All pulse sequences were capable of yielding reproducibility of around 1% coefficient of variation (CoV) or better. The best reproducibility was obtained using 2D multi-slice sequences (conventional spin echo [SE] and fluid-attenuated inversion recovery [FLAIR]), with fully automated analysis. Fully automated analysis of the longitudinal data (conventional spin echo) showed an atrophy rate of -0.5% change in BPF per year, in line with previous findings from a similar cohort of patients. In conclusion, BPF measurement is affected by both pulse sequence and segmentation method. Automated measurement has high reproducibility especially when 2D sequences are used. Semi-automated measurement may have increased accuracy, but with a decreased efficiency and reliability.

A 6-year clinical and MRI follow-up study of patients with relapsing-remitting multiple sclerosis treated with Interferon-beta.

There are few long-term clinical and magnetic resonance imaging (MRI) data on patients treated with interferon-beta (IFN-beta) for relapsing-remitting multiple sclerosis (RRMS). The aim of this study was to provide clinical and MRI data on 68 patients with RRMS treated over a 6-year period and to investigate whether a baseline MRI predicts their long-term clinical and MRI outcome. Six MRI scans were performed monthly before treatment and a further 13 scans were performed during treatment with IFN-beta, the last of which 6 years after commencement of treatment. The relapse rate, disability as measured by the Expanded Disability Status Scale (EDSS), and MRI parameters, including Gd-enhancing lesion load (Gd-LL), T2 hyperintense lesion load (T2-LL) T1 hypointense lesion load (T1-LL) and supratentorial brain volume (SBV) were measured throughout the study. The mean annual relapse rate over the 6 years was 0.52 (SD 0.67), which is significantly lower (68.6%) than the mean annual relapse rate of 1.6 observed during the 2-year period before the commencement of treatment (P < 0.01). The median EDSS score increased from 2 to 2.5, remaining stable in 60% of the patients. From the baseline scan to the final scan, there was a median increase of 7% in the T2-LL and 23.9% in the T1-LL, whilst SBV decreased by 2.7%. The increase in the EDSS over the course of the study was significantly correlated with a reduction in brain volume (r = 0.46, P = 0.001). Greater brain damage at baseline, as measured by both T2-LL and T1-LL, was significantly associated with an increase in disability over the 6 years (r = 0.44, P = 0.0009; r = 0.50, P = 0.0007, respectively). This study shows a sustained effect of IFN-beta on the relapse rate, which is lower than during the 2 years before treatment commencement. More than half the patients showed an improvement or stabilization in the EDSS score. The increment in disability was correlated with the development of brain atrophy but not with increases in lesion burden. Finally, the finding that the extent of lesion burden at the baseline was a strong predictor of increasing disability suggests that IFN-beta treatment might have a moderate effect in modifying the multiple sclerosis (MS) disease course over 6 years unless preventive treatment is started early.

Restoration of myocardial blood flow following percutaneous coronary balloon dilatation and stent implantation: assessment with qualitative and quantitative contrast-enhanced magnetic resonance imaging.

AIM: To examine the serial use of magnetic resonance imaging (MRI) to evaluate regional myocardial perfusion changes following percutaneous coronary angioplasty and stent implantation (PTCA). MATERIALS AND METHODS: Six patients with single vessel coronary artery disease (CAD) underwent contrast-enhanced first pass MRI immediately prior to (visit A) and within 7 days after (visit B) PTCA. Three sequential short axis slices were obtained after gadodiamide (Gd) bolus (0.025 mmol/kg(-1)) at rest and during adenosine. Each short axis was divided radially into eight regions of interest (ROIs). ROIs were anatomically assigned to a coronary artery territory (CAT). Stress and rest qualitative and quantitative (unidirectional extraction fraction constant (K(i)); index of myocardial perfusion reserve (MPRI) = stressK(i) / restK(i)) perfusion parameters were determined for ROI supplied by remote and stenosed/stented vessels for each visit. RESULTS: In stented ROIs the number of ROIs demonstrating normal perfusion, as opposed to reversible perfusion deficits, increased. Qualitative perfusion assessment in remote CATs was unchanged. MPRI in stenotic CATs was lower than in remote CATs at visit A (P < 0.001). Following PTCA, MPRI increased in stented CATs (P < 0.001) but was unchanged in remote CATs. CONCLUSION: Restoration of myocardial perfusion following PTCA can be delineated with qualitative and quantitative perfusion MRI. Although at present the investigation is technically complex and not perfectly sensitive or specific, MRI has the potential to be a valuable tool for patient follow-up and evaluation of revascularization strategy efficacy.

Assessment of infant physiology and neuronal development using magnetic resonance imaging.

Previous work has demonstrated both that there are substantial individual differences in the rate of physiological development,and that infants with risk factors for Sudden Infant Death Syndrome (SIDS) develop more slowly, suggesting that their increased vulnerability may be due to delayed neuronal development associated with compromised development in fetal or early neonatal life. This project aims to test the hypothesis that individual differences in the rate of physiological development of infants correlate with measurable differences in the rate of brain development as assessed by magnetic resonance imaging (MRI). Sixty infants were recruited to this study in three different groups that are known to have differing rates of physiological development. MRI was performed successfully in 49 cases at 6 weeks of age without sedation. Forty-one of these cases had full follow-up (15 normal; 19 IUGR; 11 'high risk'). Postnatal physiological development was assessed by measuring age-related deep body temperature patterns during sleep. Neuronal development was assessed by subjective analysis of MRI images and objective measurements relating to myelination using T1 and diffusion weighted (23 cases) MRI images. As expected the normal group acquired the adult temperature pattern earlier, but this was not statistically significant. All MRI scan appearances were within normal limits. Ranking cases subjectively in order of maturity revealed no significant pattern. The normal group had a significantly higher myelination score than the IUGR and 'high risk' groups (P = 0.001). This trend was also shown by the diffusion weighted myelination score but did not reach statistical significance. No significant differences were seen in both the subjective and objective MRI measurements and development of nocturnal temperature patterns. The results suggest there may be differences in neurodevelopment between the different groups at 6 weeks of age but these are not linked to late development of temperature patterns. It is therefore unlikely that this related to a global delay in maturation.

The physical basis of diffusion-weighted MRI.

Diffusion-weighted (DW) magnetic resonance imaging (MRI) is the only technique that permits a non-invasive in vivo assessment of water molecular diffusion, which reflects tissue configuration at a microscopic level. Therefore, this technique appears to be particularly useful in monitoring brain abnormalities. However, the quantitative measurement of diffusion is not without problems, which may limit the widespread use of diffusion-weighted MRI. In this report, the phenomenon of diffusion is described, together with its effect on the nuclear magnetic resonance signal. The concepts of diffusion anisotropy and diffusion tensor are also introduced, and the technical and hardware requirements are discussed.