Anatomy of the abdomen, back, and pelvis as displayed by magnetic resonance imaging: Part Two

In April 1986, magnetic resonance imaging (MRI) of the thorax and shoulder girdle was presented at the 99th Annual Meeting of the American Association of Anatomists. These images were the authors' first attempt to correlate the magnetic resonance display of the muscles and soft tissues of the chest in the coronal plane with surface gross anatomy. The original purpose of this study was to introduce the role of magnetic resonance imaging to anatomists, medical students, and the specialty of radiology. However, this approach has been expanded by imaging other sections of the body and applying the display of surface anatomy to augment the teaching of anatomy to surgical oncology, pathology, and kinesiology. This three-part article will display magnetic resonance images and will explain how magnetic imaging of the soft tissues can visually augment the teaching of gross anatomy without dissecting surface tissues.     

Anatomy of the abdomen, back, and pelvis as displayed by magnetic resonance imaging: part three

In April 1986, magnetic resonance imaging (MRI) of the thorax and shoulder girdle was presented at the 99th Annual Meeting of the American Association of Anatomists. These images were the authors' first attempt to correlate the magnetic resonance display of the muscles and soft tissues of the chest in the coronal plane with surface gross anatomy. The original purpose of this study was to introduce the role of magnetic resonance imaging to anatomists, medical students, and the specialty of radiology. However, this approach has been expanded by imaging other sections of the body and applying the display of surface anatomy to augment the teaching of anatomy to surgical oncology, pathology, and kinesiology. This three-part article will display magnetic resonance images and will explain how magnetic imaging of the soft tissues can visually augment the teaching of gross anatomy without dissecting surface tissues.     

Anatomy of the abdomen, back, and pelvis as displayed by magnetic resonance imaging: Part One

In April 1986, magnetic resonance imaging (MRI) of the thorax and shoulder girdle was presented to the 99th Annual Meeting of the American Association of Anatomists. These images were the authors' first attempt to correlate the magnetic resonance display of the muscles and soft tissues of the chest in the coronal plane with surface gross anatomy. The original purpose of this study was to introduce the role of magnetic resonance imaging to anatomists, medical students, and the specialty of radiology. However, this approach has been expanded by imaging other sections of the body and applying the display of surface anatomy to augment the teaching of anatomy to surgical oncology, pathology, and kinesiology. This three-part article will display magnetic resonance images and will explain how magnetic imaging of the soft tissues can visually augment the teaching of gross anatomy without dissecting surface tissues.     

Compromising abnormalities of the brachial plexus as displayed by magnetic resonance imaging

Magnetic resonance images (MRI) of brachial plexus anatomy bilaterally, not possible by plain radiographs or CT, were presented to the Vascular Surgery, Neurology, and the Neurosurgery departments. Patients were requested for MRI of their brachial plexus. They were referred for imaging and the imaging results were presented to the faculty and housestaff. Our technique was accepted and adopted to begin referrals for MRI evaluation of brachial plexopathy. Over 175 patients have been studied. Eighty-five patients were imaged with the 1.5 Tesla magnet (Signa; General Electric Medical Systems, Milwaukee, WI) 3-D reconstruction MRI. Coronal, transverse (axial), oblique transverse, and sagittal plane T1-weighted and selected T2-weighted pulse sequences were obtained at 4–5 mm slice thickness, 40–45 full field of view, and a 512 × 256 size matrix. Saline water bags were used to enhance the signal between the neck and the thorax. Sites of brachial plexus compromise were demonstrated. Our technique with 3-D reconstruction increased the definition of brachial plexus pathology. The increased anatomical definition enabled the vascular surgeons and neurosurgeons to improve patient care. Brachial plexus in vivo anatomy as displayed by MRI, magnetic resonance angiography (MRA), and 3-D reconstruction offered an opportunity to augment the teaching of clinical anatomy to medical students and health professionals. Selected case presentations (body builder, anomalous muscle, fractured clavicle, thyroid goiter, silicone breast implant rupture, and cervical rib) demonstrated compromise of the brachial plexus displayed by MRI. The MRI and 3-D reconstruction techniques, demonstrating the bilateral landmark anatomy, increased the definition of the clinical anatomy and resulted in greater knowledge of patient care management. © 1995 WiIey-Liss, Inc.     

Anatomy and magnetic resonance imaging of the posterolateral structures of the knee

The purpose of the present study was to provide detailed information of the morphological and radiological characteristics of the posterolateral structures of the knee. Muscles and ligaments of the posterolateral part of the knee were studied by dissections of 50 adult cadaver knees and by Magnetic Resonance Imaging (MRI) before and after dissections for comparisons. Diverse morphological characteristics of the arcuate ligament were found. The fabellofibular ligament was present in 42.1% of the knees dissected, whereas the popliteofibular ligament was found in 37.5%. A ligamentous structure, which could be called the posterior tibial ligament, was found in 31.6% of the cases that originated from the lateral part of the capsule proximally and inserted distally on the mid portion of the proximal tibia. By comparing the cross sections and the dissections of the cadaver knees, the popliteus muscle, the arcuate ligament, the fibular collateral ligament, the popliteofibular ligament, and the fabellofibular ligament could be identified in MRI. Comprehensive understanding of the posterolateral anatomy of the knee and improved identification of the structures in MRI will help clinicians to make a more accurate and noninvasive diagnosis of posterolateral instability. Clin. Anat. 10:397–404, 1997. © 1997 Wiley-Liss, Inc.     

The anatomy of the brachial plexus as displayed by magnetic resonance imaging: technique and application.

Full field of view coronal chest magnetic resonance imaging (MRI) routinely displays bilateral images of the brachial plexus, surface anatomy, and anatomic structures. Eighty patients had chest radiographs correlated with surgery for thoracic outlet syndrome. The PA chest film findings correlated with the surgical findings: smaller thoracic inlet on the concave side of the cervicothoracic spine scoliosis, shorter distance between the dorsal spine of the second or third thoracic vertebral body to the concavity of the first ribs, asymmetric clavicles and coracoid processes, synchondrosis of the first and second ribs, and muscle atrophy on the side of the clinical complaints. More than 235 patients were imaged. One hundred sixty-five of these were imaged with a 1.5-T unit and 3-D reconstruction MRI. Coronal, transverse (axial), oblique transverse, and sagittal plane T1-weighted, selected T2-weighted, and fast spine echo pulse sequences were obtained, 4- to 5-mm slice thickness, 40 to 45 cm full field of view, 512 x 256 matrix and 2 NEX. Two-dimensional time of flight (2D TOF), magnetic resonance angiography (MRA) sequences were obtained in selected patients. Coronal, transverse, and sagittal sequences were reformatted for evaluation. Saline water bags were placed between the neck and thorax to enhance the signal-to-noise ratio. Compromising abnormalities of the brachial plexus were confirmed at surgery. Compromise of the neurovascular supply seemed to be one etiology that could be demonstrated. The clinical history, technique, and anatomic bilateral brachial plexus imaging is stressed to improve patient care. The cervical rib is one of the compromising brachial plexopathies selected for this presentation.     

Anatomy of the acromial arch: correlation of anatomy and magnetic resonance imaging

Summary Based on a retrospective study of 179 MRI records covering four populations (patients presenting with impingement without known injury (n=90), post-traumatic shoulder pain (n=28), instability or dislocation (n=36) and controls (n=25)), morphologic criteria are suggested to define presumedly normal arches and arches compatible with subacromial impingement. The subacromial arch is presumed normal or without impingement if the sagittal and frontal views show it to be parallel to the humeral head, and/or if there is a fatty layer interposed between the arch and the supraspinatus m. The arch is presumed aggressive or actually capable of giving rise to impingement if, in either the sagittal or frontal view, there is a zone of narrowing of the subacromial passage with an impression of the arch on the supraspinatus tendon or tendinous thinning at this level or just lateral to this narrowed zone. Based on these criteria, study of the 179 MRI records demonstrated a significant difference of distribution of the arches in the four populations. Aggressive arches were found in 45.5% of patients with impingement, 25% of patients with posttraumatic pain, 8.9% of patients with an acute or recurrent dislocation and 12% of controls. Conversely, a presumedly normal arch was found in 56% of the controls, 55% of patients with dislocation, 25% of posttraumatic painful shoulders and only 5.5% of patients with clinical impingement. Subacromial impingement may be due to the type 3 acromial dysplasia described by Bigliani or to a thickening of the coracoacromial ligament at its acromial attachment. This study was supplemented by 15 anatomic dissections which confirmed the regularity of attachment of the coracoacromial ligament at the inferior aspect of the acromion along its lateral border.

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Anatomie de la voûte acromiale : corrélation entre anatomie et imagerie par résonance magnétique

Résumé A partir de la lecture rétrospective de 179 dossiers d'IRM représentant quatre populations (patients présentant un conflit sans traumatisme reconnu (n=90), une douleur d'épaule post-traumatique (n=28), une instabilité ou une luxation (n=36) et sujets témoins (n=25)), les auteurs proposent des critères morphologiques pour définir des voûtes présumées normales et des voûtes susceptibles de rendre compte d'un conflit sous acromial. La voûte sous acromiale est présumée normale ou non conflictuelle si, sur les vues sagittales et frontales, elle apparait parallèle à la tête humérale et/ou il existe un liseré graisseux qui s'interpose entre la voûte et le m. supra-épineux. La voûte sous acromiale est présumée agressive ou susceptible de rendre compte d'un conflit si, sur l'une des vues sagittale ou frontale, il est observé une zone de rétrécissement du défilé sous acromial avec une empreinte de la voûte sur le tendon du m. supra-épineux ou un amincissement tendineux au niveau ou juste en dehors de cette zone de rétrécissement. A partir de ces critères, la lecture des 179 dossiers d'IRM permet de mettre en évidence une différence significative de répartition des voûtes dans les quatre populations. Les voûtes agressives s'observent chez 45.5 % des patients présentant un conflit, 25 % des patients pr%esentant une douleur au décours d'un traumatisme, 8.9 % des sujets examinés au décours d'une luxation aigue ou récidivante et 12 % des sujets témoins. A l'inverse, la voûte présumée normale est retrouvée chez 56 % des sujets témoins, 55 % des patients examinés pour une luxation, 25 % des douleurs d'épaule post traumatique et seulement 5.5 % des patients présentant un conflit clinique. Le conflit sous acromial peut être le fait d'une dysplasie acromiale de type 3 décrit par Bigliani ou d'un épaississement du ligament au niveau de son insertion acromiale. Ce travail est complété par 15 dissections anatomiques qui confirment la constance de l'insertion du ligament coraco-acromial sur la face inférieure de l'acromion le long de son bord latéral.

     

Magnetic resonance imaging of the shoulder anatomy

Magnetic Resonance represents the best method for shoulder study, since it enables us to emphasize all the parts making part of this area thanks to high anatomical details and a comprehensive view of it. Conventional radiographic techniques provide only limited evaluation of soft-tissue anatomy; ultrasonography, on the other hand, allows the visualization of tendons, synovial spaces and muscle fascicles but it is shown to be unfit above all for osseous structure evaluation: TC, finally, is not being employed at present in shoulder study.     

Functional modulation of shoulder girdle stability

We have previously reported that electrical stimulation of the ulnar nerve at group I strength evokes reflex excitation of the trapezius muscle in normal human subjects. In the present study this reflex has been evoked while subjects were performing a number of different tasks. When subjects performed a task involving a high degree of manual dexterity, the reflex was larger. On the other hand, when subjects performed a task that can be achieved with virtually no movement of the hand or wrist musculature, the reflex does not appear to show any task dependency. These results support the view that in delicate tasks of the hand, such compensatory reflexes are more important than in basic mechanisms such as lifting an object. The functional consequences of these findings and their significance in relation to the possibility that these task-related reflex gain changes produce intention tremor is discussed.     

Muscle cross-section measurement by magnetic resonance imaging

Summary Muscle cross-section areas were measured by magnetic resonance imaging (MRI) in the thigh of a human cadaver,. the results being compared with those obtained by photography of corresponding anatomic macroslices. A close correlation was found between MRI and photographic evaluation, differences between the methods ranging from nil to 9.5%, depending on the scan position and the muscle groups. In vivo MRI measurements were performed on 12 female and 16 male students, the objectivity, the test-retest reliability and the variability of the MRI measurements being studied by fixing the scan position either manually or by coronary scan. The latter method appeared to be more objective and reliable. The coefficients of variation for muscle cross-section areas measured by MRI were in the range of those for the planimetry of given cross-section areas. Allowing for differentiation between several small muscle bundles in a given area, MRI proved to be a suitable method to quantify muscle cross-sections for intra- and interindividual analysis of muscle size.     

Flow-enhanced magnetic resonance imaging

A new technique for detecting blood flow in magnetic resonance imaging is proposed. This technique is tailored to enhance areas containing flow while suppressing static and nonsignal areas with the objective of optimizing the contrast of vascularized tumors. Unlike flow phase imaging, in-plane flow directionality (parallel versus antiparallel to applied flow gradient) is removed by the proposed method to reduce phase cancellation of flow signals. This signal loss is apt to occur in instances of complicated vascularity patterns consisting of many small vessels having multiple flow directions. The new flow-enhanced imaging method is compared to flow phase imaging by computer simulation of simple objects containing many small vessels. The results indicate that flow-enhanced imaging yields significantly greater detectability of regions of complicated small-vessel patterns than phase imaging.     

Molecular magnetic resonance imaging

Molecular MRI (mMRI) is a special implementation of Molecular Imaging for the non-invasive visualisation of biological processes at the cellular and molecular level. More specifically, mMRI comprises the contrast agent-mediated alteration of tissue relaxation times for the detection and localisation of molecular disease markers (such as cell surface receptors, enzymes or signaling molecules), cells (e.g. lymphocytes, stem cells) or therapeutic drugs (e.g. liposomes, viral particles). MRI yields topographical, anatomical maps; functional MRI (fMRI) provides rendering of physiologic functions and magnetic resonance spectroscopy (MRS) reveals the distribution patterns of some specific metabolites. mMRI provides an additional level of information at the molecular or cellular level, thus extending MRI further beyond the anatomical and physiological level. These advances brought by mMRI are mandatory for MRI to be competitive in the age of molecular medicine. mMRI is already today increasingly used for research purposes, e.g. to facilitate the examination of cell migration, angiogenesis, apoptosis or gene expression in living organisms. In medical diagnostics, mMRI will pave the way toward a significant improvement in early detection of disease, therapy planning or monitoring of outcome and will therefore bring significant improvement in the medical treatment for patients.In general, Molecular Imaging demands high sensitivity equipment, capable of quantitative measurements to detect probes that interact with targets at the pico- or nanomolar level. The challenge to detect such sparse targets can be exemplified with cell surface receptors, a common target for molecular imaging. At high expression levels (bigger than 106 per cell) the receptor concentration is approx. 10(15) per ml, i.e. the concentration is in the micromole range. Many targets, however, are expressed in even considerably lower concentrations. Therefore the most sensitive modalities, namely nuclear imaging (PET and SPECT) have always been at the forefront of Molecular Imaging, and many nuclear probes in clinical use today are already designed to detect molecular mechanisms (such as FDG, detecting high glucose metabolism). In recent years however, Molecular Imaging has commanded attention from beyond the field of nuclear medicine. Further imaging modalities to be considered for molecular imaging primarily include optical imaging, MRI and ultrasound.     

Parallel magnetic resonance imaging

Parallel imaging has been the single biggest innovation in magnetic resonance imaging in the last decade. The use of multiple receiver coils to augment the time consuming Fourier encoding has reduced acquisition times significantly. This increase in speed comes at a time when other approaches to acquisition time reduction were reaching engineering and human limits. A brief summary of spatial encoding in MRI is followed by an introduction to the problem parallel imaging is designed to solve. There are a large number of parallel reconstruction algorithms; this article reviews a cross-section, SENSE, SMASH, g-SMASH and GRAPPA, selected to demonstrate the different approaches. Theoretical (the g-factor) and practical (coil design) limits to acquisition speed are reviewed. The practical implementation of parallel imaging is also discussed, in particular coil calibration. How to recognize potential failure modes and their associated artefacts are shown. Well-established applications including angiography, cardiac imaging and applications using echo planar imaging are reviewed and we discuss what makes a good application for parallel imaging. Finally, active research areas where parallel imaging is being used to improve data quality by repairing artefacted images are also reviewed.     

Evaluation of skin tumors by magnetic resonance imaging

In vivo magnetic resonance imaging (MRI) is a powerful noninvasive technique in medical diagnosis; however, its application to analyze skin disorders is still at initial stages. To check whether MRI can be used as a noninvasive tool to analyze skin tumors, we carried out MRI of mice after treatment with benzo[a]pyrene (BP), a well known carcinogen. MRI was done on whole mice and was particularly focused on various layers and regions of interest of the skin: dermis, epidermis, and tumor. Initial MRIs of mice bearing skin tumors of 4, 8, 12, and 16 weeks after inducing BP clearly revealed the appearance of tumor. The MRIs of tumor-bearing mice with 20-week-old tumor development showed invasion to adjacent internal anatomic structures. The MRI data were in good agreement with the extent of cellular atypia and neoplastic changes that are typical of squamous cell carcinoma as noticed from the histopathologic findings. Therefore, MRI seems to have the potential to evaluate the tumor invasions equally well as that of histopathology or other clinical findings.     

Exploring the frontiers of magnetic resonance imaging

New developments in magnetic resonance imaging are highlighted, including multiecho-multislice high-resolution imaging, special purpose coils, multiplanar imaging, thin slices, hybrid imaging processing, flow imaging, heart gating, paramagnetic contrast material, and wider application of spectroscopy.     

Oblique magnetic resonance imaging of the bronchi

The trachea and main bronchi of a supine patient in a magnetic resonance (MR) scanner are not contained in a single standard coronal plane, but instead intersect this coronal plane at some angle, usually 20 degrees - 35 degrees. We have developed a new MR imaging protocol to determine the oblique imaging plane which best contains the trachea and main bronchi. The resulting oblique images simplify anatomical identification, and allow the user to select additional oblique planes which cut any desired portion of main bronchus in true cross section. Accurate lumen shapes and areas may then be extracted from these cross-sectional images. The method does not require the patient to be moved or rotated, and does not require hardware modification. We demonstrate the clinical application of the protocol with both a normal volunteer and a patient with an endobronchial tumor. The use of gradient echo pulse sequences together with this protocol to distinguish between vessels and bronchi is presented. We provide phantom verification to demonstrate the quantitative accuracy of the method to provide lumen areas.     

Evaluation of ectopic pregnancy by magnetic resonance imaging.

Patients (n = 37) suspected of ectopic pregnancy were prospectively evaluated with magnetic resonance (MR) imaging to assess the capability of MR imaging in the diagnosis of ectopic pregnancy. Five levels of confidence were defined: diagnostic, suspicious, equivocal, questionable, and negative. Tubal wall enhancement and presence of tubal haematoma or gestational sac-like structure were considered diagnostic findings. There were 21 diagnostic, two suspicious, eight equivocal, and six negative findings. MR findings were compared with the surgical findings in 18 patients. Surgical confirmation was obtained in 12 diagnostic, two suspicious, and four equivocal studies. Using the MR diagnostic criteria for tubal pregnancy, MR had 12 true positive, three true negative, three false negative, and no false positive results for the diagnosis of tubal pregnancy. Retrospective analysis of the signal intensity of haematoma and ascites was performed for these 18 surgically confirmed cases. The predominant signal intensity of tubal haematoma was an intermediate signal on T1-weighted image (WI) and a low signal on T2WI. Ascites showed signal intensity higher than that of urine on T1WI in 100% of 13 cases. In conclusion, MR imaging with use of intravenous contrast material allows a specific diagnosis of tubal pregnancy, recognizing tubal wall enhancement and fresh tubal haematoma.     

Nerves on magnetic resonance imaging

Nerves are often visualized on magnetic resonance imaging (MRI) studies of the soft tissues on the chest and shoulder girdle. To learn the reasons for the contrast between the nerves and adjacent tissues, the authors obtained a fresh specimen containing part of the brachial plexus nerves from the left axilla and compared MRI with x-ray projections and photomicrographs of histologic sections. The results suggest that the high signals from the nerves stand out in contrast to the low signals from their rich vascular supply.