Current Magnetic Resonance Imaging Research Articles

Integrated PET/MR imaging: Automatic attenuation correction of flexible RF coils

Flexible radiofrequency (RF) surface coils used in simultaneous PET/MR imaging are currently disregarded in PET attenuation correction (AC) since their position and individual geometry are unknown in whole-body patient scans. The attenuation of PET emission data due to the presence of RF surface coils has been investigated by several research groups but so far no automatic approach for the incorporation of RF surface coils into PET AC has been described. In this work, an algorithm is presented and evaluated which automatically determines the position of multiple RF surface coils and corrects for their attenuation of the PET emission data. The presented algorithm nonrigidly registers pre-acquired CT-based three-dimensional attenuation templates of RF surface coils into attenuation maps used for PET AC. Transformation parameters are obtained by nonrigid B-spline landmark registration of marker positions in the CT-based attenuation templates of the RF surface coils to marker positions in the current MR images of the patient. The use of different marker patterns enables the registration algorithm to distinguish multiple partly overlapping RF surface coils. To evaluate the registration algorithm, two different PET emission scans of a NEMA standard body phantom with six active lesions and of a large rectangular body phantom were performed on an integrated whole-body PET/MR scanner. The phantoms were scanned with and without one (NEMA phantom scan) or three (large body phantom scan) flexible six-channel RF surface coils placed on top. Additionally, the accuracy and performance of the algorithm were evaluated on volunteer scans (n=5) and on a patient scan using a typical clinical setup of three RF surface coils. Overall loss of true counts due to the presence of the RF surface coils was 5.1% for the NEMA phantom, 3.6% for the large body phantom, and 2.1% for the patient scan. Considerable local underestimation of measured activity concentration up to 15.4% in the top part of the phantoms and 15.5% for a lesion near the body surface of the patient was measured close to the high attenuating hardware components of the RF coils. The attenuation maps generated by the registration algorithm reduced the quantification errors due to the RF surface coils to values ranging from -3.9% to 4.3%. Concerning the volunteer examinations, the attenuation templates of the three RF surface coils were registered to their correct positions with an overall accuracy of about 3 mm. The presence of flexible RF surface coils leads to considerable local errors in the simultaneously measured PET activity concentration up to 15.5% especially in regions close to the coils. The presented automatic algorithm accurately and reliably reduces the PET quantification errors caused by multiple partly overlapping flexible RF surface coils to values of 4.3% or better.

MRI of the Elbow: Techniques and Spectrum of Disease

Magnetic resonance imaging (MRI) of the elbow allows for high-resolution evaluation of osseous and soft-tissue structures, including ligaments, tendons, nerves, and muscles. Multiple imaging techniques and pulse sequences exist. The purpose of this article is to update orthopaedic surgeons on current MRI techniques and illustrate the spectrum of elbow pathology detectable by MRI. We searched MEDLINE with use of the keywords "MRI" and "elbow" for studies less than five years old evaluating MRI techniques. These papers, our experience, and textbooks reviewing elbow MRI provided the information for this article. We discuss the essentials and applications of the following techniques: (1) conventional, non-gadolinium-enhanced MRI; (2) gadolinium-enhanced MRI; and (3) magnetic resonance arthrography. The classic MRI appearances of occult fractures, loose bodies, ulnar collateral ligament injuries, lateral collateral ligament complex injuries, biceps tendon injuries, triceps tendon injuries, lateral epicondylitis, medial epicondylitis, septic arthritis, osteomyelitis, osteochondritis dissecans, compression neuropathies, synovial disorders, and various soft-tissue masses are reviewed. MRI is a valuable, noninvasive method of elbow evaluation. This article updates orthopaedic surgeons on the various available MRI techniques and facilitates recognition of the MRI appearances of the most commonly seen pathologic elbow conditions.

Limited utility of current MRI criteria for distinguishing multiple sclerosis from common mimickers: primary and secondary CNS vasculitis, lupus and Sjogren’s syndrome

Background: Magnetic resonance imaging (MRI) criteria play an important role in making an earlier diagnosis of multiple sclerosis (MS) in patients presenting with clinically isolated syndrome. Objective: The objective of this paper is to determine whether MRI criteria may be used to distinguish MS from primary and secondary central nervous system (CNS) vasculitis, lupus, and Sjogren’s syndrome. Methods: MRI criteria were applied retrospectively to images for patients with clinically definite MS (CDMS), primary CNS vasculitis, secondary CNS vasculitis, and autoimmune disorders including systemic lupus erythematosus (SLE) and Sjogren’s syndrome. Classical statistics and Bayesian analyses were performed. Results: Overall modified Barkhof’s MRI criteria were statistically significant in distinguishing CDMS (60%) from SLE/Sjogren’s syndrome (17%, p = 0.0173) but not in distinguishing CDMS from primary CNS vasculitis (50%, p = 0.7376) or secondary CNS vasculitis (58%, p = 1.0000). Four of the five other MRI criteria tested were demonstrated to be superior to modified Barkhof’s criteria in predicting MS: nine or more T2 lesions (a component of Barkhof’s criteria), one or more ovoid periventricular T2 lesions, one or more perpendicular periventricular T2 lesions, and one or more T2 lesions larger than 6 mm. Conclusions: MRI criteria, including the modified Barkhof’s criteria, were unsuccessful in distinguishing MS from primary CNS vasculitis or secondary CNS vasculitis and mildly successful in distinguishing MS from SLE/Sjogren’s syndrome.

Magnetic Resonance Imaging of Ischemia Viability Thresholds and the Neurovascular Unit

Neuroimaging has improved our understanding of the evolution of stroke at discreet time points helping to identify irreversibly damaged and potentially reversible ischemic brain. Neuroimaging has also contributed considerably to the basic premise of acute stroke therapy which is to salvage some portion of the ischemic region from evolving into infarction, and by doing so, maintaining brain function and improving outcome. The term neurovascular unit (NVU) broadens the concept of the ischemic penumbra by linking the microcirculation with neuronal-glial interactions during ischemia reperfusion. Strategies that attempt to preserve the individual components (endothelium, glia and neurons) of the NVU are unlikely to be helpful if blood flow is not fully restored to the microcirculation. Magnetic resonance imaging (MRI) is the foremost imaging technology able to bridge both basic science and the clinic via non-invasive real time high-resolution anatomical delineation of disease manifestations at the molecular and ionic level. Current MRI based technologies have focused on the mismatch between perfusion-weighted imaging (PWI) and diffusion weighted imaging (DWI) signals to estimate the tissue that could be saved if reperfusion was achieved. Future directions of MRI may focus on the discordance of recanalization and reperfusion, providing complimentary pathophysiological information to current compartmental paradigms of infarct core (DWI) and penumbra (PWI) with imaging information related to cerebral blood flow, BBB permeability, inflammation, and oedema formation in the early acute phase. In this review we outline advances in our understanding of stroke pathophysiology with imaging, transcending animal stroke models to human stroke, and describing the potential translation of MRI to image important interactions relevant to acute stroke at the interface of the neurovascular unit.

Current MR Imaging Lipid Detection Techniques for Diagnosis of Lesions in the Abdomen and Pelvis

One application of the unique capability of magnetic resonance (MR) imaging for characterizing soft tissues is in the specific detection of lipid. Adipose tissue may be abundant in the body, but its presence in a lesion can greatly limit differential diagnostic considerations. This article reviews MR imaging fat detection techniques and discusses lesions in the abdomen and pelvis that can be readily diagnosed by using these techniques. Traditional fat detection methods include inversion-recovery and chemically selective fat-suppression pulse sequences, with the former being less sensitive to field heterogeneity and less tissue specific than the latter. Chemical shift-based sequences, which exploit the inherent resonance frequency difference between lipid and water to depict intracytoplasmic fat, have great utility for evaluating hepatic steatosis and lesions such as adrenal and hepatic adenomas, hepatocellular carcinoma, focal lipomatosis of the pancreas, and adrenal cortical carcinoma. The signal from large amounts of fat can be suppressed by using a narrow radiofrequency pulse for selective excitation of fat protons (ie, fat saturation imaging), a technique that increases image contrast resolution and highlights lesions such as contrast-enhancing tissue, edema, and blood products. This technique is especially useful for evaluating renal angiomyolipomas, adrenal myelolipomas, ovarian teratomas, and liposarcomas. MR spectroscopy is a promising method for quantifying absolute liver fat concentration and changes in hepatic triglyceride content during treatment. New and evolving techniques include magnetization transfer and modified Dixon sequences. A solid understanding of these techniques will help improve the interpretation of abdominal and pelvic imaging studies.

Magnetic Resonance Imaging of the Hand and Wrist: Techniques and Spectrum of Disease

Magnetic resonance imaging (MRI) is an excellent imaging modality for the evaluation of pathologic processes of the hand and wrist. MRI of the hand and wrist provides high-resolution imaging of osseous structures and soft-tissue structures (including ligaments, tendons, nerves, and muscles) through the use of multiple imaging techniques and pulse sequences. This article updates orthopaedic surgeons on current MRI techniques and illustrates the spectrum of hand and wrist disease detectable by MRI. We searched PubMed with use of the keywords “MRI” plus “hand” or “wrist” for studies less than five years old evaluating MRI techniques. On the basis of a review of the recently published literature and the authors’ experience, we define and describe the applications of the following: (1) conventional, non-gadolinium-enhanced MRI, (2) gadolinium-enhanced MRI, and (3) MR arthrography. We also describe the classic MRI appearance of lesions commonly evaluated by MRI, including occult fracture, triangular fibrocartilage complex injury, interosseous ligament injury, extrinsic carpal ligament injury, thumb ulnar collateral ligament injury, traumatic tendon injury, finger pulley injury, ulnar impaction syndrome, tendinopathy, Kienbock disease, posttraumatic scaphoid osteonecrosis, infection, inflammatory arthropathy, compression neuropathy, and various soft-tissue masses. The incorporation of dedicated surface coils and higher-strength magnets has improved the quality of magnetic resonance imaging (MRI) scanners substantially over the last decade. By manipulating the scanning parameters when performing an MRI examination, contrast differences between tissues can be emphasized on the basis of inherent tissue properties known as T1 and T2. T1-weighted images are generally regarded as best for illustrating anatomic detail. T2-weighted sequences highlight alterations in water content, which are characteristic of most pathologic conditions. Short tau inversion recovery (STIR) and fat-suppressed T2-weighted images accentuate fluid and edema and are the most sensitive for detecting pathologic changes in both bone and soft tissue. The intravenous administration of a gadolinium-based contrast agent …

Correlation Between Magnetic Resonance Imaging and Clinical Outcomes After Cartilage Repair Surgery in the Knee

Background: Magnetic resonance imaging (MRI) is often used to assess cartilage after surgical repair. The correlation between MRI and clinical outcomes is not well understood. Hypothesis: Postoperative MRI findings correlate with clinical outcome measures in patients after articular cartilage surgery of the knee. Study Design: Meta-analysis. Methods: A systematic review of the literature was performed to identify studies in which MRI and clinical outcomes were correlated after autologous chondrocyte implantation (ACI), osteochondral autograft transfer system (OATS), or microfracture. Studies that reported correlation coefficients (r) for different MRI parameters were then included in a meta-analysis. Results: A total of 26 studies were identified for inclusion in this systematic review, 15 of which were included in the meta-analysis. Most of the studies (n = 19) involved ACI, although studies were available for OATS (n = 5) and microfracture (n = 4). The strongest MRI correlates with clinical outcomes after ACI were graft hypertrophy (r = 0.72) and repair tissue signal (r = 0.71). After microfracture, the strongest MRI correlates were the Henderson score (r = 0.97), subchondral edema (r = 0.77), and repair tissue signal (r = 0.76). Correlations after OATS were not as strong, with defect fill (r = 0.53) and repair tissue structure (r = 0.51) being the strongest. Conclusion: The MRI findings do correlate with clinical outcomes after cartilage repair surgery in the knee, although the specific parameters that correlate best vary by the type of procedure performed. No current MRI classification system has been shown to correlate with clinical outcomes after all types of cartilage repair surgery.

New MR Imaging Assessment Tool to Define Brain Abnormalities in Very Preterm Infants at Term

WM injury is the dominant form of injury in preterm infants. However, other cerebral structures, including the deep gray matter and the cerebellum, can also be affected by injury and/or impaired growth. Current MR imaging injury assessment scales are subjective and are challenging to apply. Thus, we developed a new assessment tool and applied it to MR imaging studies obtained from very preterm infants at term age. MR imaging scans from 97 very preterm infants (< 30 weeks' gestation) and 22 healthy term-born infants were evaluated retrospectively. The severity of brain injury (defined by signal abnormalities) and impaired brain growth (defined with biometrics) was scored in the WM, cortical gray matter, deep gray matter, and cerebellum. Perinatal variables for clinical risks were collected. In very preterm infants, brain injury was observed in the WM (n=23), deep GM (n=5), and cerebellum (n=23). Combining measures of injury and impaired growth showed moderate to severe abnormalities most commonly in the WM (n=38) and cerebellum (n=32) but still notable in the cortical gray matter (n=16) and deep gray matter (n=11). WM signal abnormalities were associated with a reduced deep gray matter area but not with cerebellar abnormality. Intraventricular and/or parenchymal hemorrhage was associated with cerebellar signal abnormality and volume reduction. Multiple clinical risk factors, including prolonged intubation, prolonged parenteral nutrition, postnatal corticosteroid use, and postnatal sepsis, were associated with increased global abnormality on MR imaging. Very preterm infants demonstrate a high prevalence of injury and growth impairment in both the WM and gray matter. This MR imaging scoring system provides a more comprehensive and objective classification of the nature and extent of abnormalities than existing measures.

A Supervised Learning Approach for Crohn's Disease Detection Using Higher-Order Image Statistics and a Novel Shape Asymmetry Measure

Increasing incidence of Crohn's disease (CD) in the Western world has made its accurate diagnosis an important medical challenge. The current reference standard for diagnosis, colonoscopy, is time-consuming and invasive while magnetic resonance imaging (MRI) has emerged as the preferred noninvasive procedure over colonoscopy. Current MRI approaches assess rate of contrast enhancement and bowel wall thickness, and rely on extensive manual segmentation for accurate analysis. We propose a supervised learning method for the identification and localization of regions in abdominal magnetic resonance images that have been affected by CD. Low-level features like intensity and texture are used with shape asymmetry information to distinguish between diseased and normal regions. Particular emphasis is laid on a novel entropy-based shape asymmetry method and higher-order statistics like skewness and kurtosis. Multi-scale feature extraction renders the method robust. Experiments on real patient data show that our features achieve a high level of accuracy and perform better than two competing methods.

Consistent Neurodegeneration and Its Association with Clinical Progression in Huntington's Disease: A Coordinate-Based Meta-Analysis

Background: The neuropathological hallmark of Huntington's disease (HD) is progressive striatal loss starting several years prior to clinical onset. In the past decade, whole-brain magnetic resonance imaging (MRI) studies have provided accumulating evidence for widely distributed cortical and subcortical atrophy in the early course of the disease. Objective: In order to synthesize current morphometric MRI findings and to investigate the impact of clinical and genetic features on structural changes, we performed a coordinate-based meta-analysis of voxel-based morphometry (VBM) studies in HD. Methods: Twenty HD samples derived from 17 studies were integrated in the analysis comparing a total of 685 HD mutation carriers [345 presymptomatic (pre-HD) and 340 symptomatic (symp-HD) subjects] and 507 controls. Convergent findings across studies were delineated using the anatomical likelihood estimation approach. Effects of genetic and clinical parameters on the likelihood of observing VBM findings were calculated by means of correlation analyses. Results: Pre-HD studies featured convergent evidence for neurodegeneration in the basal ganglia, amygdala, thalamus, insula and occipital regions. In symp-HD, cerebral atrophy was more pronounced and spread to cortical regions (i.e. inferior frontal, premotor, sensorimotor, midcingulate, frontoparietal and temporoparietal cortices). Higher cytosine-adenosine-guanosine repeats were associated with striatal degeneration, while parameters of disease progression and motor impairment additionally correlated with cortical atrophy, especially in sensorimotor areas. Conclusion: This first quantitative meta-analysis in HD demonstrates the extent of striatal atrophy and further consistent extrastriatal degeneration before clinical conversion. Sensorimotor areas seem to be core regions affected in symp-HD and, along with widespread cortical atrophy, may account for the clinical heterogeneity in HD.

Neuroimaging in aphasia treatment research: Quantifying brain lesions after stroke

New structural and functional neuroimaging methods continue to rapidly develop, offering promising tools for cognitive neuroscientists. In the last 20 years, advanced magnetic resonance imaging (MRI) techniques have provided invaluable insights into how language is represented and processed in the brain and how it can be disrupted by damage to, or dysfunction of, various parts of the brain. Current functional MRI (fMRI) approaches have also allowed researchers to purposefully investigate how individuals recover language after stroke. This paper presents recommendations for quantification of brain lesions derived from discussions among international researchers at the Neuroimaging in Aphasia Treatment Research Workshop held at Northwestern University (Evanston, Illinois, USA). Methods for detailing and characterizing the brain damage that can influence results of fMRI studies in chronic aphasic stroke patients are discussed. Moreover, we aimed to provide the reader with a set of general practical guidelines and references to facilitate choosing adequate structural imaging strategies that facilitate fMRI studies in aphasia treatment research.

Diagnostic accuracy of magnetic resonance imaging for an acute pulmonary embolism: results of the ‘IRM‐EP’ study

Magnetic resonance imaging (MRI) has not been validated as an alternative diagnostic test to computed tomography angiography (CTA) in patients with suspicion of a pulmonary embolism (PE). To evaluate performance of current MRI technology in diagnosing PE, in reference to a 64-detector CTA. Prospective investigation including 300 patients with a suspected PE, referred for CTA after assessment of clinical probability and D-dimer testing. MRI protocol included unenhanced, perfusion and angiographic sequences. MRI results were interpreted by two independent readers, to evaluate inter-reader agreement. Sensitivity and specificity were evaluated globally and according to PE location and to clinical probability category. Of 300 enrolled patients, 274 were analyzed and 103 (37.5%) had a PE diagnosed by CTA. For patients with conclusive MRI results (72% for reader 1, 70% for reader 2), sensitivity and specificity were 84.5% (95% confidence interval [CI], 74.9-91.4%) and 99.1% (95% CI, 95.1-100.0%), respectively, for reader 1, and 78.7% (95% CI, 68.2-87.1%) and 100% (95% CI, 96.7-100.0%) for reader 2. After exclusion of inconclusive MRI results for both readers, inter-reader agreement was excellent (kappa value: 0.93, 95% CI: 0.88-0.99). Sensitivity was better for proximal (97.7-100%) than for segmental (68.0-91.7%) and sub-segmental (21.4-33.3%) PE (P < 0.0001). Sensitivity was similar for both readers within each clinical probability category. Current MRI technology demonstrates high specificity and high sensitivity for proximal PE, but still limited sensitivity for distal PE and 30% of inconclusive results. Although a positive result can aid in clinical decision making, MRI cannot be used as a stand-alone test to exclude PE.

Evaluation of novel combined carbogen USPIO (CUSPIO) imaging biomarkers in assessing the antiangiogenic effects of cediranib (AZD2171) in rat C6 gliomas

The recently described combined carbogen USPIO (CUSPIO) magnetic resonance imaging (MRI) method uses spatial correlations in independent imaging biomarkers to assess specific components of tumor vascular structure and function. Our study aimed to evaluate CUSPIO biomarkers for the assessment of tumor response to antiangiogenic therapy. CUSPIO imaging was performed in subcutaneous rat C6 gliomas before and 2 days after treatment with the potent VEGF-signaling inhibitor cediranib (n = 12), or vehicle (n = 12). Histological validation of Hoechst 33342 uptake (perfusion), smooth muscle actin staining (maturation), pimonidazole adduct formation (hypoxia) and necrosis were sought. Following treatment, there was a significant decrease in fractional blood volume (-43%, p < 0.01) and a significant increase in hemodynamic vascular functionality (treatment altered ΔR(2) *(carbogen) from 1.2 to -0.2 s(-1) , p < 0.05). CUSPIO imaging revealed an overall significant decrease in plasma perfusion (-27%, p < 0.05) following cediranib treatment, that was associated with selective effects on immature blood vessels. The CUSPIO responses were associated with a significant 15% reduction in Hoechst 33342 uptake (p < 0.05), but no significant difference in vascular maturation or necrosis. Additionally, treatment with cediranib resulted in a significant 40% increase in tumor hypoxia (p < 0.05). The CUSPIO imaging method provides novel and more specific biomarkers of tumor vessel maturity and vascular hemodynamics, and their response to VEGF-signaling inhibition, compared to current MR imaging biomarkers utilized in the clinic. Such biomarkers may prove effective in longitudinally monitoring tumor vascular remodeling and/or evasive resistance in response to antiangiogenic therapy.

Cerebral Microinfarcts: A Systematic Review of Neuropathological Studies

Vascular cognitive impairment is an umbrella term for cognitive dysfunction associated with and presumed to be caused by vascular brain damage. Autopsy studies have identified microinfarcts as an important neuropathological correlate of vascular cognitive impairment that escapes detection by conventional magnetic resonance imaging (MRI). As a frame of reference for future high-resolution MRI studies, we systematically reviewed the literature on neuropathological studies on cerebral microinfarcts in the context of vascular disease, vascular risk factors, cognitive decline and dementia. We identified 32 original patient studies involving 10,515 people. The overall picture is that microinfarcts are common, particularly in patients with vascular dementia (weighted average 62%), Alzheimer's disease (43%), and demented patients with both Alzheimer-type and cerebrovascular pathology (33%) compared with nondemented older individuals (24%). In many patients, multiple microinfarcts were detected. Microinfarcts are described as minute foci with neuronal loss, gliosis, pallor, or more cystic lesions. They are found in all brain regions, possibly more so in the cerebral cortex, particularly in watershed areas. Reported sizes vary from 50 μm to a few mm, which is within the detection limit of current high-resolution MRI. Detection of these lesions in vivo would have a high potential for future pathophysiological studies in vascular cognitive impairment.

New Insights in Perinatal Arterial Ischemic Stroke by Assessing Brain Perfusion

Perinatal arterial ischemic stroke (AIS) is an important cause of long-term morbidity in children. Thus, there is an urgent need to better understand the mechanisms of stroke in newborns in order to develop effective treatment and prevention strategies. The purpose of this study was to assess brain perfusion within the first month of life in newborns with AIS. In this study, magnetic resonance imaging (MRI) and perfusion imaging by arterial spin labeling (ASL) were used to assess brain perfusion in four term newborns with AIS. One patient had a stroke within the territory of the right middle cerebral artery (MCA); the other three patients had a stroke within the territory of the left MCA. None of them displayed any hemorrhagic component. All four patients demonstrated abnormal brain perfusion in the stroke area. Cerebral blood flow (CBF) within the stroke area was increased in patient # 1. In all other three patients, CBF was decreased within the stroke center and increased in the periphery of the stroke area. These results show the feasibility of the ASL sequence in newborns with AIS and support its addition to the current MRI protocol used in these newborns as it provides useful information on brain hemodynamics. Its value for identifying salvageable tissue in newborns needs to be further assessed, as well as its potential role in stroke follow-up and for tissue-specific treatment screening.

PMD49 The Potential Role of Magnetic Resonance Imaging (MRI) in Axillary Node Assessment of Early Breast Cancer: An Economic Evaluation

THE POTENTIAL ROLE OF MAGNETIC RESONANCE IMAGING (MRI) IN AXILLARY NODE ASSESSMENT OF EARLY BREAST CANCER: AN ECONOMIC EVALUATION Meng Y1, Ward SE1, Cooper K1, Harnan SE1, Wyld L2 1University of Sheffield, Sheffield, UK, 2Royal Hallamshire Hospital, Sheffield, UK OBJECTIVES: Surgical techniques including sentinel lymph node biopsy (SLNB) and 4-node sampling (4-NS) are currently used for axillary nodal assessment of early breast cancer (EBC) in the UK. Such procedures are associated with adverse effects, (AEs), in particular scarring, pain, general anaesthesia and occasional lymphoedema which may impact on long term quality of life. Magnetic resonance imaging (MRI) is a non-invasive technique offering the potential to avoid such AEs. A range of MRI techniques, including USPIO (ultrasmall superparamagnetic iron oxide contrast agent)-enhanced and gadolinium-enhanced MRI exist, however diagnostic accuracy of these techniques may be lower than for surgical techniques. An economic evaluation was undertaken to compare MRI with surgical techniques for assessment of axillary lymph node metastases in patients with EBC. METHODS: The costs and benefits of replacing SLNB or 4-NS with MRI (replacement strategy) or adding MRI before the surgical techniques (addition strategy) were modelled using discrete-event simulation in SIMUL8®. A systematic review was undertaken to obtain effectiveness outcomes of the MRI techniques, whilst resource use data and health related utilities were obtained from the literature. RESULTS: Our results predict that a replacement strategy for MRI, based on the pooled estimate of all MRI techniques, dominates the baseline SLNB and 4-NS strategies, as a result of avoiding AEs from surgical techniques. However this strategy leads to more false-positive and false-negative cases. The MRI addition strategy may also be cost-effective, but is subject to greater uncertainty. USPIO-enhanced MRI produces the most favourable cost effectiveness ratio, but the evidence is based on studies with small patient numbers. CONCLUSIONS: These results suggest that there is a potential role for MRI in axillary node assessment of EBC. Based on current evidence USPIOenhanced MRI offers the most cost effective option, but further large studies are required to obtain high quality evidence on diagnostic accuracy.

Assessment of lesion pathology in a new animal model of MS by multiparametric MRI and DTI

Magnetic resonance imaging (MRI) is the gold standard for the detection of multiple sclerosis (MS) lesions. However, current MRI techniques provide little information about the structural features of a brain lesion with inflammatory cell infiltration, demyelination, gliosis, acute axonal damage and axonal loss. To identify methods for a differentiation of demyelination, inflammation, and axonal damage we developed a novel mouse model combining cuprizone-induced demyelination and experimental autoimmune encephalomyelitis. MS-like brain lesions were assessed by T1-weighted, T2-weighted, and magnetization transfer MRI as well as by diffusion tensor imaging (DTI). T2-weighted MRI differentiated control and diseased mice, while T1-weighted MRI better reflected the extent of inflammation and axonal damage. In DTI, axonal damage and cellular infiltration led to a reduction of the axial diffusivity, whereas primary demyelination after cuprizone treatment was reflected by changes in radial but not axial diffusivity. Importantly, alterations in radial diffusivity were less pronounced in mice with demyelination, inflammation, and acute axonal damage, indicating that radial diffusivity may underestimate demyelination in acute MS lesions. In conclusion, the combined information from different DTI parameters allows for a more precise identification of solely demyelinated lesions versus demyelinated and acutely inflamed lesions. These findings are of relevance for offering individualized, stage-adapted therapies for MS patients.

Quantification of renal perfusion: Comparison of arterial spin labeling and dynamic contrast‐enhanced MRI

To provide the first comparison of absolute renal perfusion obtained by arterial spin labeling (ASL) and separable compartment modeling of dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI). Moreover, we provide the first application of the dual bolus approach to quantitative DCE-MRI perfusion measurements in the kidney. Consecutive ASL and DCE-MRI acquisitions were performed on six rabbits on a 1.5 T MRI system. Gadolinium (Gd)-DTPA was administered in two separate injections to decouple measurement of the arterial input function and tissue uptake curves. For DCE perfusion, pixel-wise and mean cortex region-of-interest tissue curves were fit to a separable compartment model. Absolute renal cortex perfusion estimates obtained by DCE and ASL were in close agreement: 3.28 ± 0.59 mL/g/min (ASL), 2.98 ± 0.60 mL/g/min (DCE), and 3.57 ± 0.96 mL/g/min (pixel-wise DCE). Renal medulla perfusion was 1.53 ± 0.35 mL/g/min (ASL) but was not adequately described by the separable compartment model. ASL and DCE-MRI provided similar measures of absolute perfusion in the renal cortex, offering both noncontrast and contrast-based alternatives to improve current renal MRI assessment of kidney function.

MO‐D‐220‐08: Quantitative Embryonic Central Nervous System Imaging Using High‐ Frequency Annular Arrays

Purpose: The central nervous system (CNS) is the first organ to develop during mammalian embryogenesis and the CNS dynamically evolves well into the postnatal stages. Abnormal CNS phenotypes are normally visualized in vivo or with fixed samples using magnetic resonance imaging (MRI). Current MRI coil technology does not permit early‐stage in vivo imaging of the mouse embryo CNS. Here, a custom‐made, high‐frequency‐ultrasound annular‐array system operating at 38 MHz was utilized to perform in vivo imaging of early‐stage mouse embryo CNS. Methods: A custom‐made ultrasound scanning system using a piezopolymer‐based annular array was utilized for the imaging studies. The array had five equal‐area elements, a 6 mm total aperture, and a 12 mm geometric focus. The scanning system was designed to perform five scans across an object in order to acquire all transmit‐to‐receive data (25 data sets). This data was then synthetically focused to achieve enhanced depth of field and lateral resolution. In addition, the system utilized a coded‐excitation scheme to enhance SNR and penetration depth, and a respiratory gate to reduce motion artifacts. A full 3D volumetric data set could be acquired in approximately 2 minutes. Results: In vivo, in utero volumetric data were acquired from 78 mouse embryos spanning embryonic days 10 to 13. The data sets were processed with a semi‐automated image segmentation algorithm and brain volumes were calculated. The results indicated that during these mid‐gestational stages, there was an increase in CNS volume of 38% while volumetric renderings revealed the complex remodeling of the neuroarchitecture showing more cell proliferation than increase in brain mass. Conclusions: High‐frequency annular arrays with coded excitation offer an effective means of acquiring in vivo, in utero ultrasound data of the embryonic mouse and can be used to rapidly analyze the normal or abnormal development of the CNS during longitudinal studies.This research was supported by the National Institutes of Health (EB008606).

Susceptibility-Weighted Imaging of the Brain: Current Utility and Potential Applications

Susceptibility-Weighted Imaging (SWI) is a relatively new magnetic resonance imaging (MRI) sequence relying on susceptibility differences between adjacent tissues to produce an image. It is extremely sensitive for detection of blood products (hemosiderin, ferritin), deoxygenated blood, calcium, iron, and small vein depiction. Little information is available in the literature to describe common findings seen using this imaging sequence. This article is an comprehensive review of appearances across the spectrum of brain pathology encountered in routine clinical practice. A retrospective review of 400 MRI Brain examinations was performed by one fellowship trained Neuroradiologist with 5 years experience (SB) and one general radiologist (RR). Agreement was by consensus observing normal and pathological imaging features seen in SWI sequences. Results are presented as a comprehensive pictorial review highlighting the key imaging findings observed and new directions using SWI. SWI is an extremely useful adjunct to current MRI sequences of the brain and is advocated for inclusion into routine Neuroimaging protocols.