Surface Coil Magnetic Resonance Research Articles

The signal-to-noise ratio of nuclear magnetic resonance surface coils and application to a lossy dielectric cylinder model. I. Theory

Surface coils are used in magnetic resonance imaging (MRI) for their high signal-to-noise ratio (S/N) when placed near the-region to be imaged. However, their optimization for high field MRI systems is hampered by the lack of understanding of the electromagnetic effects taking place at high frequencies when a coil is placed near the human body. The aim of this work was to calculate the S/N of surface coils using complete solutions to Maxwell's equations and also to study the high frequency effects and parameters determining the S/N. Here the authors present a general approach to the computation of the S/N of surface coils using the reciprocity principal and the complex Poynting vector for arbitrary coil and body geometries. This approach is then applied to the case of the human body modeled as an infinitely long homogeneous dielectric cylinder exhibiting both conductive and dielectric losses. The S/N of a coil of unspecified geometry facing the cylinder is derived using a dyadic Green's function. Complete solutions for the fields of a dipolar source arbitrarily located in the cylinder are first derived, and applying the reciprocity principle, the authors deduce the fields created at the dipole position by a coil excited with a unit radiofrequency current. These yield the expressions for the power dissipated in the cylinder, for its reciprocal the noise picked up by the coil, and also for the signal received. Any coil geometry and any coil or source position can be evaluated with this infinite cylinder model. It is valid at all frequencies and for any tissue parameter. The general approach to the computation of the S/N of MRI coils can be applied to other body geometries as well.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Myocardial Energy Metabolism in the Newborn Lamb In Vivo during Pacing-Induced Changes in Oxygen Consumption

Myocardial energy metabolism was studied in newborn sheep to determine whether the metabolic responses to pacing-induced increases in heart rate were similar to those previously found during catecholamine stimulation. Open-chest newborn sheep, 3 to 9 d old (n = 11), underwent atrial pacing at a respiratory rate harmonic just above the intrinsic heart rate. Pacing rate was increased by 30 beats/min every 5 min until conduction block or a drop in systemic arterial pressure occurred. Phosphorous metabolites were monitored simultaneously (n = 7) using a 31P magnetic resonance surface coil over the heart within a magnet operating at 4.7 tesla. Myocardial oxygen consumption was monitoring via an extracorporeal shunt from the coronary sinus. Rate pressure product increased with heart rate and was found to relate to myocardial oxygen consumption (r = 0.75), which increased maximally by 47 +/- 9% due to increases in coronary blood flow. Phosphocreatine/ATP ratio decreased significantly, and calculated ADP increased between baseline and peak performance but returned to near baseline levels during recovery at the initial pacing rate. These findings indicate that intracellular high-energy phosphate concentrations do change with alterations in myocardial oxygen consumption induced by cardiac pacing in the newborn. These changes are similar to those found during epinephrine infusion. Furthermore, the ATP hydrolysis products probably participate in myocardial respiratory regulation in the newborn in vivo.

Decision Making in Pediatric Ophthalmology

Medical decision making is difficult to teach and, in general, neglected in the medical literature. The difficulty in mastering management of clinical problems is compounded by the increasingly technical diagnostic techniques now commonly available, as well as by the increasingly specific subcategorization of disease entities. The latest in the Clinical Decision Making Series from Mosby-Year Book,<i>Decision Making in Pediatric Ophthalmology</i>, addresses this problem by describing in a concise format an approach to decisions in the evaluation and treatment of pediatric ophthalmic problems. Like the preceding texts in the series, including<i>Decision Making in Ophthalmology</i>and<i>Decision Making in Pe-</i><i>diatrics</i>, this book distills a huge amount of information on the management of clinical problems into its 348 pages. The 137 topics contained within the book range from the routine (amblyopia, infantile esotropia) to the exotic (high-resolution surface coil magnetic resonance imaging of the pediatric eye) and are divided

Comparison of Standardized Echography With Magnetic Resonance Imaging to Measure Extraocular Muscle Size

Using both standardized echography and high-resolution, surface coil magnetic resonance imaging, we measured the transverse diameter of recti extraocular muscles to evaluate comparative accuracy. Maximum transverse diameter of each rectus muscle in primary gaze was measured in 39 orbits of 20 subjects by using standardized A-scan echography. In the same orbits, we obtained multiple coronal magnetic resonance imaging planes by using a surface coil to span the anteroposterior extent of each orbit. Digital image analysis with the National Institutes of Health Image program was used to measure transverse muscle diameter. Average size for each rectus muscle was similar for the echographic and magnetic resonance imaging techniques. However, linear regressions of individual ultrasound against magnetic resonance imaging measurements showed coefficients of determination (R2) moderate (0.29) for inferior recti muscles and low (< or = 0.11) for other recti muscles. For most recti muscles, significant variability in echographic estimates of muscle width results from factors other than true muscle size. Results indicate that ultrasound measurements of muscle size in individual patients should be interpreted cautiously.

A multivariable analysis of clinical factors predicting for pathological features associated with local failure after radical prostatectomy for prostate cancer

Purpose : A multivariate analysis is used to determine the predictive value of pretreatment clinical indicators on pathologic features associated with local failure after radical prostatectomy in patients with prostate cancer. Methods and Materials : A retrospective review of the pathologic findings of 235 patients with adenocarcinoma of the prostate treated between 1990 and 1993 with a radical retropubic prostatectomy was performed. The preoperative clinical data including the serum prostate specific antigen, clinical stage, Gleason sum, and endorectal magnetic resonance scan findings are used to identify patients prior to definitive treatment who would be at high risk for having pathologic features associated with local failure at radical prostatectomy. Outcome prediction curves are constructed from a logistic regression multivariate analysis displaying the probability of pathologic involvement of the seminal vesicle, extracapsular disease, or positive surgical margins as a function of the preoperative prostate specific antigen and Gleason sum for the cases when the endorectal magnetic resonance scan is positive, negative, or not included in the multivariate analysis. Results : Factors identified on multivariate analysis as significant predictors of seminal vesicle invasion include endorectal magnetic resonance scan findings ( p < 0.0001), and preoperative prostate specific antigen ( p = 0.017). Endorectal magnetic resonance scan findings ( p = 0.0016), preoperative prostate specific antigen ( p = 0.0002), and Gleason sum ( p < 0.0001) were significant predictors of extracapsular extension and preoperative prostate specific antigen ( p < 0.0001) and Gleason sum ( p = 0.03) were significant predictors of disease extending to the margins of resection. Clinical stage was not a significant predictor ( p > 0.05) of pathologic features associated with local failure on multivariate analysis. As a single modality, endorectal surface coil magnetic resonance imaging was accurate 93%, 69%, and 72% of the time for predicting seminal vesicle invasion, transcapsular disease, and final pathologic stage, respectively. Failure to recognize microscopic penetration of the capsule found at the time of pathologic evaluation in a prostate gland with a grossly intact capsule accounts for the majority (70%) of the staging inaccuracies. Conclusions : The use of the endorectal surface coil magnetic resonance scan findings in conjunction with both the serum prostate specific antigen and Gleason sum improves the clinical accuracy of predicting those patients at high risk for clinically unsuspected extraprostatic disease. In particular, for the subgroup of patients with moderately elevated prostate specific antigen (> 10–20 ng/mL) and intermediate grade clinically organ confined prostate cancer [Gleason sum: 5–7] where the specificity of these tests to predict for occult extraprostatic disease is suboptimal, the additional information obtained from the endorectal coil magnetic resonance scan allows the physician to definitively subgroup these patients into low and high risk for seminal vesicle invasion or transcapsular disease.

Rectal tumor stage: correlation of endorectal MR imaging and pathologic findings.

To develop magnetic resonance (MR) imaging criteria for staging rectal cancer. Thirty-six patients with rectal tumors underwent MR imaging with an endorectal surface coil. MR images were compared with specimens from the resected tumor. Rectal wall layers were reliably demonstrated. The MR imaging-determined tumor stage agreed with pathologic findings in 81% of cases. A retrospective review found the integrity of the rectal wall layers at the lesion center an accurate criterion for interpreting the local extent of the lesion. Lymph nodes as small as 2 mm were demonstrated. Although sensitive for demonstrating perirectal adenopathy, MR imaging had a specificity of only 72% for N1 disease. Endorectal surface coil MR imaging shows promise for staging rectal lesions. Additional studies are necessary to further establish criteria for interpreting the images.

Use of Endorectal Surface Coil Magnetic Resonance Imaging for Local Staging of Prostate Cancer

A total of 111 patients with clinically localized prostate cancer (stage A or B) underwent endorectal surface coil magnetic resonance imaging (MRI) for preoperative staging of the disease. Of the patients 43 with advanced disease on endorectal surface coil MRI (33 with stage C and 10 with stage D disease) received alternative therapy, as did 21 with stage B disease on MRI The overall staging accuracy for the remaining 47 patients was 68%, with a 74% accuracy rate in staging advanced disease and a 91% accuracy rate for depiction of seminal vesicle involvement. Failure to recognize microscopic extracapsular disease was responsible for the majority of staging inaccuracies in this highly select group of patients. Endorectal surface coil MRI provides extremely high resolution images of the prostate and periprostatic structures, and is an exciting new modality for local staging of prostatic carcinoma.

Effect of Transposition Surgery on Rectus Muscle Paths by Magnetic Resonance Imaging

To evaluate effects of transposition on extraocular rectus muscle paths in middle and deep orbit. The effect of various transposition procedures was assessed in five patients, using surface coil magnetic resonance imaging (MRI), performed with controlled gaze before and after surgery. Path changes were compared with those expected under conventional concepts of functional orbital anatomy, quantified by biomechanical modeling. Vertical rectus transpositions of 6 to 10 mm produced changes in muscle paths of 3 mm or less, assessed posterior to the equator of the globe. Lateral rectus transpositions as large as 10 mm resulted in almost no movement of muscle bellies. Conventional modeling predicted much larger changes. The authors observed less movement of rectus muscle bellies relative to orbital walls than would be expected under the traditional assumption that transposed muscles follow the shortest path from origin to insertion. This implies that middle and deep orbital tissues (connective tissues and compartmentalized orbital fat) constrain the paths of rectus muscle bellies, preventing them from sliding freely to follow their transposed insertions. The authors propose that these tissues function as "pulleys" elastically coupled to the orbital wall, and that they are important determinants of extraocular muscle function.

Current Assessment of Spinal Degenerative Disease With Magnetic Resonance Imaging

Radiography (plain roentgenography, myelography, computed tomography (CT), computed tomographic myelography) has been used to identify morphologic changes involving the various components of the diskovertebral unit. Added to this armamentarium of imaging techniques is magnetic resonance (MR) imaging, with its superior ability to define anatomy, its improved contrast sensitivity, and its potential to provide unique biochemical and physiologic information. The authors review the current use of MR imaging in defining degenerative changes in the spine including the various patterns of herniation, annular tears, canal stenosis, and the use of gadolinium-diethylenetriamine-pentaacetic acid for previously unoperated and operated patients. Prospective studies have compared surface-coil MR imaging, CT, and myelography in the evaluation of disk herniation and stenosis and found an 82.6% accuracy between MR imaging and surgical findings for the type and location of the disease. Recent experience with precontrast and postcontrast MR imaging in the postoperative lumbar spine indicated that it was 96% accurate in differentiating scar from disk in 44 patients at 50 reoperated levels. Three-dimensional imaging is, more and more, becoming an integral part of routine MR imaging. The theoretical and practical advantages of three-dimensional imaging are several and include a theoretical increase in the signal-to-noise ratio over two-dimensional imaging (by the square root of the number of partitions selected), the ability to obtain thin contiguous slices from the volume without the problem of cross-talk found in two-dimensional imaging, more accurate slice thickness than that achieved in two-dimensional imaging, and a reduction in susceptibility artifacts. Different three-dimensional techniques are capable of providing either high or low signal intensity cerebrospinal fluid (CSF), with excellent suppression of CSF pulsation artifacts. Certain sequences provide a high enough signal intensity that a computer algorithm may be used to display the CSF in a rotating three-dimensional manner, similar to a myelogram. This three-dimensional myelographic image has the potential of providing the clinician with a global assessment of the CSF spaces, an advantage previously lacking with other imaging techniques.

Endorectal surface coil MR imaging of prostatic carcinoma with the inversion‐recovery sequence

The value of inversion-recovery (IR) sequences in the diagnosis and staging of prostatic carcinoma with magnetic resonance (MR) imaging was studied. Twenty-six patients with carcinoma of the prostate were imaged at 1.5 T with an endorectal surface coil and with a variety of IR sequences and a set of spin-echo (SE) sequences for comparison. Ex vivo prostate specimens were imaged again at the same field strength. The two images were correlated with histologic sections. Cancer was identified with MR imaging in 96% of patients. Of the tumors more than 4 mm in diameter, 87% were identified on T2-weighted SE images, whereas only 26% were identified on IR images. However, IR images may be more useful in local staging of carcinoma. Gross capsular infiltration was present in only two patients; however, it was detectable (and excluded in five other patients) by means of IR images. It was not detectable on SE images. The high quality of images obtained with the endorectal coil was confirmed. The authors conclude that addition of the IR sequence to MR imaging with the endorectal coil may improve the usefulness of this examination.

Orbital fractures: surface coil MR imaging.

Twenty-six patients with orbital fractures diagnosed with plain radiography and computed tomography were examined with surface coil magnetic resonance (MR) imaging. Fifteen patients had blow-out fractures, and 11 had maxillofacial complex fractures. In all patients with blow-out fractures, the location of the fracture was precisely indicated by the presence of prolapsed orbital fat. Incarceration of the extraocular muscle or orbital fat was correctly diagnosed with MR imaging, which was less sensitive in depicting maxillofacial fractures but was useful in assessment of soft-tissue involvement. Postoperative follow-up MR studies provided valuable information about the cause of motility impairment. While T1-weighted images are useful for the detection of the fracture site, both T1- and T2-weighted images are usually necessary for evaluating soft-tissue lesions. The results of this study indicate that surface coil MR imaging is an important adjunct procedure in the diagnosis and treatment of orbital fractures.

Magnetic resonance imaging of temporomandibular joint after surgical treatment of internal derangement

Sagittal and coronal surface coil magnetic resonance imaging was performed on 21 patients who about 2 years earlier had surgery for temporomandibular joint internal derangement. Surgical procedure included disk repositioning (23 joints) and diskectomy (seven joints). At the time of reimaging, 20 joints showed recurrence of pain and 10 joints were asymptomatic. Extensive fibrous tissue was seen in the joint space and in the joint capsule in 13 of the 20 painful joints, whereas minimal fibrous tissue in the lateral capsule wall was seen in 3 of the 10 nonpainful joints. Fibrous tissue was surgically confirmed in 10 of the painful joints. Disk displacement was seen in 11 of the 23 joints that had surgical disk repositioning. Disk displacement was seen in both painful (9/17) and nonpainful joints (2/6). It was concluded that magnetic resonance imaging is an excellent method for postoperative imaging of the temporomandibular joint and that attention should be directed to the presence or absence and extension of the fibrous tissue in the joint space and in the joint capsule.

Magnetic Resonance Imaging of the Temporomandibular Joint: Preliminary Evaluation of Partial Flip Angle Three-Dimensional Volume Acquisitions Against Conventional Single and Multiecho Pulse Sequences

The authors imaged 20 temporomandibular joints (TMJs) in 20 patients with high field surface coil magnetic resonance imaging, to compare the accuracy and the clinical utility of thin section partial flip angle (PFA) three dimensional (3D) volume acquisitions with T1-weighted images (T1WI), spin echo, multiecho, long TR/short and long TE images, PFA gradient recalled acquisition in the steady state (GRASS) images in the diagnosis of internal derangement of the TMJ. Pathological conditions demonstrated on imaging studies included disk derangement, joint effusion, and osteocartilaginous lesions, such as degenerative arthritis, osteoporosis, osteochondritis dissecans and early avascular necrosis of the mandibular condyle.

Prostate cancer: local staging with endorectal surface coil MR imaging.

Endorectal surface coil magnetic resonance (MR) imaging was used to stage the local extent of prostate cancer in 22 patients. The endorectal coil images were acquired with a 10-12-cm field of view and a 4-mm section thickness. All pathologic specimens were reviewed by one pathologist. Endorectal surface coil MR imaging was 82% accurate in the differentiation of stage B from stage C cancer. One case was overestimated, and three cases were underestimated. The three underestimated cases consisted of two cases of microscopic capsular invasion and one case of minimal seminal vesicle invasion. In a comparison of retrospective, blinded readings of endorectal coil and body coil images, there was an average improvement in accuracy of 16% in staging prostate cancer with endorectal coil images.

4812761 Electrically parallel equal phase resonant loops for nuclear magnetic resonance surface coils

A nuclear magnetic resonance measurement system is disclosed which includes, in combination, means for generating an applied main magnetic field, and an array of at least two radio frequency current loops. The loops are electrically connected in parallel, and are oriented in a generally planar relationship with respect to each other. The loops are connected in phase with respect to each other so that the component of magnetization generated by the loops which orthogonal to the direction of the applied main magnetic field is in the same general direction. A capacitor is preferably electrically connected in parallel with the loops.

Magnetic Resonance Imaging in Diagnosis and Follow-up of Minimal Thyroid Ophthalmopathy.

We report a case of minimal thyroid ophthalmopathy treated with intravenous methylprednisolone, in which precise identification of the involved muscle was possible with the use of surface coil magnetic resonance (MR) imaging. Intravenous methylprednisolone was more effective than the oral prednisolone as judged by orbital MR imaging. MR imaging is one of the useful tools in the diagnosis and assessment of treatment in this field.

Developmental adaptations in cytosolic phosphate content and pH regulation in the sheep heart in vivo.

This study examines adaptations in myocardial cytosolic phosphate content and buffering capacity that occur in vivo as a function of development. Phosphate metabolites were monitored in an open chest sheep preparation using a 31P magnetic resonance surface coil over the left ventricle. Newborn lambs (aged 4-9 d, n = 5) underwent exchange transfusion with adult blood to reduce blood-borne 2,3-diphosphoglycerate contamination of the heart monophosphate and phosphomonoester resonances, thus allowing determination of these phosphate concentrations. The blood-exchanged newborns and mature controls (aged 30-60 d, n = 5) were infused with 0.4 N hydrochloric acid to decrease pH from greater than 7.35 to less than 7.00. Simultaneously, intracellular and extracellular pH were determined from the chemical shifts of the respective phosphate peaks and compared to arterial blood pH. Findings were as follows: (a) diphosphoglycerate contribution to the cardiac spectrum was found to be negligible, (b) significant decreases in cytosolic phosphate (P less than 0.03) and phosphomonoester (P less than 0.01) content occurred with maturation, and (c) large decreases in extracellular pH (greater than 0.5 U) in both groups were similarly associated with only small changes in intracellular pH (less than 0.1 U). Change in cytosolic phosphate content implies that alterations occur in the phosphorylation potential with resulting effects on regulation of myocardial respiration, and cardiac energetics.

Magnetic Resonance Imaging of Lumbar Disc Herniation

Fifty-three patients with surgically confirmed lumbar disc herniation at 55 levels were studied retrospectively to compare the diagnostic accuracy of high-field strength surface coil magnetic resonance imaging (MRI) with that of myelography. Disc herniation was classified into three groups according to MRI findings, namely, unilateral single-disc herniation, central single-disc herniation, and multilevel disc herniation. Magnetic resonance imaging diagnosis of unilateral single-disc herniation was extremely reliable, so myelography was considered to be unnecessary. Conversely, MRI findings of central single-disc herniation and multilevel disc herniation were less definite, in that myelography was necessary in locating the disc causing symptoms.

Magnetic Resonance Imaging in Vogt-Koyanagi-Harada Syndrome

Vogt - Koyanagi - Harada syndrome (VKH) is a multisystem disorder characterized by chronic bilateral non-rhegmatogenous retinal detachments and granulomatous uveitis associated with meningeal, auditory, and cutaneous findings. 1 The dermatologic findings (poliosis, alopecia, perilimbal and cutaneous vitiligo) and auditory disturbances (tinnitus, dysacousia, and vertigo) may occur weeks to months after the onset of the disease, making the initial diagnosis difficult. 1,2 We report a case where the diagnosis of VKH was aided by the use of surface coil magnetic resonance imaging (MRI). Report of a Case. —A 34-year-old woman of Hispanic/black descent presented with a 3-week history of progressive visual loss, metamorphopsia, photophobia, and headache. Best-corrected visual acuity was 20/400 OD and 20/200 OS. Slit-lamp examination showed 1+ anterior chamber and vitreous cells. Ophthalmoscopy disclosed focal yellow-white lesions at the level of the retinal pigment epithelium with multiple overlying areas of exudative retinal detachment in addition to a mild papillitis. Fluorescein

Facial pain, headache, and temporomandibular joint inflammation.

We studied one hundred patients with suspected temporomandibular joint (TMJ) arthropathy in whom 64 also complained of headache and/or facial pain, using high field surface coil magnetic resonance (MR) imaging, and found that headache and facial pain are commonly observed in association with inflammatory arthropathy of the TMJ. Each patient complained of pain and/or tenderness localized to the immediate vicinity of at least one TMJ. Pathologic joint effusion was demonstrated by MR in 88 of the painful joints studied. Significant meniscus displacement, with or without meniscus deformity and alteration of intrinsic signal intensity was present in 94 of the 100 painful joints examined. Fascial inflammation and atrophy of the ipsilateral muscles of mastication were observed occasionally with painful joints. There were no mechanical TMJ symptoms, such as joint clicking, crepitus or locking in 14 internally deranged and painful joints, 12 of which exhibited joint effusion and local inflammation. At least 80 patients described occlusal changes within 12 months of imaging. 28 of the pathologic joints in the series underwent subsequent meniscectomy, including routine histologic evaluation of surgical material. We conclude that internal derangement and inflammation of the TMJ should be considered in patients with unexplained headache and/or facial pain, even if mechanical TMJ symptoms are absent.