Effects of hemodynamics on thromboembolism in coronary stents and prototype flow cells in vitro

Thromboembolism was studied as heparinized (3 U/ml) bovine blood was gravity fed through a conduit with a deployed coronary stent or a prototype flow cell. The initial flow rate was established with a pinch valve, and monitored with a clamp-on ultrasonic probe. Emboli production was continuously monitored using a light scattering microemboli detector. Accumulated thrombus at the end of the experiment was assessed gravimetrically in stents or by magnetic resonance imaging in flow cells. Hemodynamic parameters were varied to assess their effects on thromboembolism. With the flow cells, the hemodynamics were controlled by varying the geometry of the stagnation zones. With the stents, the flow characteristics were altered by placing 75% stenoses upstream and/or downstream of the stent. The average values of the shear stress and residence time around the stent were modeled using the commercial fluid dynamics software FLUENT. Combining the computed hemodynamic parameters with the experimental results showed that 1) thrombus accumulation decreased with increasing shear stress and increased with increasing residence time; 2) embolization was promoted by high shear, and did not correlate with the amount of thrombus accumulated at the end of the experiment; and 3) a reconfiguration of the magnetic resonance imaging system is necessary to monitor thrombus accumulation continuously.     

Accuracy of seven different tests for the diagnosis of Helicobacter pylori infection and the impact of H2-receptor antagonists on test results

The financial burden for the evaluation of patients for acoustic neuroma in an otolaryngology practice is substantial. Patients with sudden sensorineural hearing loss represent a portion of that population seen with unilateral, asymmetric auditory symptoms who require investigation for acoustic neuroma. For these patients, gadolinium-enhanced magnetic resonance imaging is the diagnostic gold standard. Auditory brain stem response testing has been used in the past as a screening test for acoustic neuroma, but its apparent sensitivity has fallen as the ability to image smaller acoustic neuromas has improved. Fast spin echo magnetic resonance imaging techniques without gadolinium have been shown to be as effective in the detection of acoustic neuroma as contrast-enhanced magnetic resonance imaging. Limited nonenhanced fast spin echo magnetic resonance imaging now provides an inexpensive alternative for high-resolution imaging of the internal auditory canal and cerebellopontine angle. Fast spin echo magnetic resonance imaging can now be done at a cost approximating auditory brain stem response testing while providing the anatomic information of contrast-enhanced magnetic resonance imaging. Cost analysis was done in the cases of 58 patients with sudden sensorineural hearing loss by comparing the costs for routine workup and screening of acoustic neuroma with the cost of fast spin echo magnetic resonance imaging with the use of screening protocols based on literature review. The potential cost savings of evaluating patients with sudden sensorineural hearing loss with fast spin echo magnetic resonance imaging for acoustic neuroma was substantial, with a 54% reduction in screening costs. In an era of medical economic scrutiny, fast spin echo magnetic resonance imaging has become the most cost-effective method to screen suspected cases of acoustic tumors at our institution by improving existing technology while reducing the cost of providing that technology and eliminating charges for impedance audiometry, auditory brain stem response testing, and contrast-enhanced magnetic resonance imaging.     

Functional surgery of ceruminoma of the external and/or middle ear

We made a prospective study of 58 patients with suspected internal derangement of the knee. They were examined by magnetic resonance imaging using 3-D gradient echo intermediate-weighted studies before having an arthroscopy. The preoperative clinical assessment was found to have a diagnostic sensitivity of 77% and a specificity of 43%, compared with 100% and 63% respectively for magnetic resonance imaging. Comparison of magnetic resonance imaging and arthroscopy confirmed the accuracy of magnetic resonance imaging in the diagnosis of internal derangement but the results for articular cartilage lesions were much less good, with a sensitivity of only 18% but a specificity of 100%. Acceptance of the magnetic resonance imaging findings could have resulted in a 29% reduction in the number of arthroscopies without missing any significant meniscal lesion.     

Integrated MR imaging approach to valvular heart disease

With development of cine and velocity encoded magnetic resonance imaging, it is now feasible to detect and quantify aortic and mitral stenosis and regurgitation accurately. In addition, magnetic resonance imaging has the capabilities to assess simultaneously left and right ventricular mass, volumes, and function precisely. The high accuracy and reproducibility of magnetic resonance imaging in quantification of regurgitation and ventricular function has the potential to provide improved monitoring of therapy and optimal timing of surgery in patients with valvular dysfunction. In comparison to echocardiography and angiography, some current limitations of magnetic resonance imaging to an integrated approach of valvular heart disease exist, which may be removed with future refinement of magnetic resonance imaging technology for cardiovascular imaging.     

A combined surgical and radiologic technique for creating a functional neo-endocervical canal in a case of partial congenital cervical atresia

OBJECTIVE: To recanalize the endocervical canal in a patient with partial congenital cervical atresia. DESIGN: Case report. SETTING: University hospital. PATIENT: A 16-year-old girl referred with a history of primary amenorrhea, polycystic ovaries, and intermittent abdominal pain. Physical examination revealed a normal vagina and external cervical os, but magnetic resonance imaging revealed a solid endocervical tract. INTERVENTION(S): At laparotomy the endometrial cavity was accessed transfundally and outlined by injection of water-soluble contrast. A trocar needle was guided transvaginally into the uterus, the tract was dilated, and a 12F stent was placed. Oral contraceptives (OCs) and antibiotics were continued postoperatively. MAIN OUTCOME MEASURE(S): Hysterosalpingography and clinical follow-up. RESULT(S): The operation and postoperative course were uneventful. Withdrawal bleeding occurred at 8 weeks, after discontinuation of the OCs, at which time the stent was expelled. Later follow-up revealed recurrent narrowing, and the stent was replaced for 14 more weeks. After stent removal, regular menses continued (7 months to date). CONCLUSION: In select cases of congenital cervical atresia, recanalization may be safely performed with the use of the combined surgical-radiologic technique described, with good short-term outcome.     

Magnetic resonance imaging of the musculoskeletal system. Part 6. The Shoulder

The role of magnetic resonance imaging in the diagnosis and treatment of patients with shoulder pain has increased remarkably in recent years, largely because of improved resolution of images and increased experience of musculoskeletal radiologists. In rotator cuff disease/impingement and instability, magnetic resonance imaging adds a new dimension to the clinical findings through the noninvasive visualization of either the pathology itself or frequently associated abnormalities. It is the associated abnormalities that are depicted in instability: glenoid irregularities, labral tears, capsular laxity, and Hill-Sachs deformities. Glenoid, labral, and Hill-Sachs abnormalities can be assessed with either magnetic resonance imaging or computed tomography arthrography. Magnetic resonance imaging has the advantages of noninvasiveness, multiplanar imaging capability and exquisite soft tissue contrast. In rotator cuff disease, magnetic resonance imaging depicts the status of the rotator cuff itself, revealing partial and full thickness tears, allowing an estimation of size and quality of tendon edges. Possible impingement sites can be identified. Primary instability with secondary impingement may be first suspected on magnetic resonance imaging. Postoperative complications, including recurrent tendon detachment, deltoid dehiscence, and infection, are clarified. Unsuspected but clinically important lesions, such as neoplasm, osteonecrosis, and ganglion with entrapment of the suprascapular nerve, each have characteristic magnetic resonance imaging appearances.     

Imaging cardiac structure and pump function

This article describes magnetic resonance imaging approaches for assessing cardiac structure and myocardial pump function. The article is divided into cardiac structure and ventricular function. Throughout, representative images are included. There are numerous applications of magnetic resonance imaging for assessing cardiac structure and function, and magnetic resonance imaging compared favorably to other imaging modalities.     

Electron transfer kinetics at a biotin/avidin patterned glassy carbon electrode

STUDY DESIGN: Comparison of findings in plain radiography and conventional tomography with findings in plain radiography and magnetic resonance imaging of the upper cervical spine in consecutive patients with rheumatoid arthritis and with known or suspected abnormalities of the cervical spine. OBJECTIVES: To determine whether plain radiography and magnetic resonance imaging provide enough information to dispense with tomography in investigations of cervical spine involvement in rheumatoid arthritis. SUMMARY OF BACKGROUND DATA: With the recent advances in magnetic resonance imaging technology and the proliferation of magnetic resonance imaging techniques for specific clinical conditions. METHODS: Twenty-eight patients with rheumatoid arthritis and with known or suspected abnormalities of the cervical spine underwent a clinical neurologic examination; plain radiography, including full flexion lateral radiography; anteroposterior and lateral tomography at C1-C2; and magnetic resonance imaging at the same level in neutral position and in flexion. Two radiologists evaluated one image set consisting of plain radiography and conventional tomographic images and another image set consisting of plain radiography and magnetic resonance images, for each patient. RESULTS: Compared with conventional tomography and plain radiography, magnetic resonance imaging and plain radiography showed cystic lesions and erosions of the odontoid process and vertical atlantoaxial subluxation more often, showed anterior subluxation as often, and showed lateral atlantoaxial subluxation less often. CONCLUSION: Magnetic resonance imaging produces sufficiently distinct images of destruction of the odontoid and subluxations for it to replace conventional tomography in investigations of upper cervical spine involvement in rheumatoid arthritis.     

Vascular compression of the oculomotor nerve disclosed by thin-slice magnetic resonance imaging

PURPOSE: To describe the thin-slice magnetic resonance imaging features of vascular compressive oculomotor nerve paresis. METHODS: We performed thin-slice (2 mm thick) magnetic resonance imaging of the brainstem in a 74-year-old woman with right partial oculomotor nerve paresis using spoiled gradient recalled acquisition in the steady state. RESULTS: Thin-slice magnetic resonance images disclosed that the right oculomotor nerve was compressed and dislocated superiorly and laterally by the tortuous basilar artery. No other abnormalities were observed. CONCLUSION: This is the first case report of vascular compressive oculomotor nerve paresis disclosed by thin-slice magnetic resonance imaging.     

A comparison of magnetic resonance and computed tomographic image quality after the implantation of tantalum and titanium spinal instrumentation

STUDY DESIGN: Tantalum- and titanium-based lumbar interbody fusion devices were implanted into two fresh human cadavers, and magnetic resonance and computed tomographic imaging were performed to evaluate adjacent spinal structures and the amount of metallic artifact. OBJECTIVE: The objective of this study was to prospectively compare the preliminary results of magnetic resonance imaging and computed tomography scanning image quality after the implantation of both titanium and tantalum spinal implants. SUMMARY OF BACKGROUND DATA: The availability of tantalum and titanium spinal implants brings theoretical magnetic resonance imaging compatibility along with several other desirable characteristics. The magnetic resonance imaging and computed tomographic imaging of tantalum spinal instrumentation has never been studied previously or compared with titanium instrumentation. METHODS: Titanium and tantalum spinal implants produced for anterior spinal fusion were each placed at two levels in the lumbar spine of two fresh cadaver specimens. Sequential spin echo T1-weighted and T2-weighted magnetic resonance imaging studies and computed tomographic scans were obtained. The resulting images were then graded to describe and compare the behavior of tantalum metal in magnetic resonance imaging and computed tomographic studies. RESULTS: Good T1 and T2 images were obtained that allowed visualization of the neural structures with minimal artifact. The optimal T1 images for tantalum metal were similar in quality to the optimal T1 parameters for titanium metal. T2 images for both tantalum and titanium metal were obtained with similar results for both metals. Gradient echo magnetic resonance imaging scans of both were poorly imaged with a large amount of artifact. Computed tomographic studies of tantalum implants produced a large amount of metal artifact when compared with computed tomographic studies of titanium implants. CONCLUSIONS: High-quality magnetic resonance imaging studies can be obtained after the implantation of both titanium and tantalum spinal instrumentation. Both of the metals produce similar images on magnetic resonance imaging studies with comparable amounts of metallic artifact. High-quality computed tomographic scans of titanium implants can be obtained with minimal distortion secondary to artifact. However, computed tomographic scanning is not the imaging modality of choice for the tantalum spinal implants because of the large amounts of artifact.     

Predictive signs of discogenic lumbar pain on magnetic resonance imaging with discography correlation

STUDY DESIGN: The correlation between discogenic lumbar pain and disc morphology was investigated by using magnetic resonance imaging and discography. OBJECTIVES: To assess the various pathologic parameters seen on magnetic resonance imaging in patients with discogenic lumbar pain and to correlate them with observations on discography. SUMMARY OF BACKGROUND DATA: Although numerous previous studies on the subject have been performed, the correlations between various pathologic findings on magnetic resonance imaging and pain reproduction by provoked discography have not been explained fully. METHODS: One hundred and one lumbar discs in 39 patients were studied with magnetic resonance imaging and pain provocation discography. When pain reproduction under discography was concordant, various pathologic parameters on magnetic resonance imaging were analyzed by three statistical parameters to determine the associated magnetic resonance imaging findings. RESULTS: Radial tears commonly are demonstrated on magnetic resonance imaging in discs with concordant pain on discography. The presence of these tears is not a reliable predictor of a painful disc on discography. Although a high-intensity zone on T2-weighted images is a relatively reliable predictor of pain, the statistical values were lower than those in previous studies. Massive degeneration and severe disc height loss were rare in this population. These findings were good predictors of pain on disc injection. CONCLUSIONS: Although the lumbar intervertebral discs with posterior combined anular tears are likely to produce pain, the validity of these signs for predicting discogenic lumbar pain is limited.     

The eye

In recent years, the growing application of computed tomography (CT) and magnetic resonance (MR) imaging evaluation of the orbit and globe have dramatically increased the role of imaging and, hence, that of the radiologist in assessing ophthalmologic disorders. This article discusses magnetic resonance imaging features of the most common and less common ocular pathologies, with particular emphasis on the potential of magnetic resonance imaging in the field of ophthalmology.     

Magnetic resonance imaging of the musculoskeletal system. Part 9. Primary Tumors

Magnetic resonance imaging, because of its exquisite soft tissue contrast, has dramatically improved the ability to preoperatively stage primary osseous and soft tissue neoplasms. This technique also has allowed the monitoring of the effects of chemotherapy and the screening for recurrence of neoplasms. The role of magnetic resonance imaging in the preoperative evaluation of the patient with a suspected primary osseous or soft tissue neoplasm is outlined, instances where magnetic resonance imaging potentially may make a specific diagnosis are outlined, the importance of gadolinium enhancement as an adjunct to native magnetic resonance imaging is stressed, and an algorithm for followup of patients after chemotherapy or definitive surgical treatment is presented. In all cases, the magnetic resonance images should be correlated with the plain film, which is still an important aspect of the diagnosis of osseous lesions.     

Magnetic resonance imaging of the musculoskeletal system. Part 4. The knee

Since its introduction to musculoskeletal imaging in the early 1980s, magnetic resonance imaging has proven to be an excellent technique for evaluating patients with knee problems. Studies have shown it to be accurate in the identification of abnormalities of the menisci, ligaments, patellofemoral joints, and other soft tissue and osseous structures in the knee. The main advantages of magnetic resonance imaging are its noninvasive nature and its high accuracy and negative predictive value in evaluating the menisci and anterior cruciate ligament. Magnetic resonance imaging has been shown to be useful in the detection and diagnosis of various traumatic and nontraumatic knee abnormalities. It has also proved useful in the diagnosis of occult or unsuspected bone lesions. Magnetic resonance imaging can therefore help in the selection of those patients who need therapeutic arthroscopy. There is evidence that magnetic resonance imaging of the knee is a cost effective screening technique when used in conjunction with the clinical findings in patients who are candidates for arthroscopy. Magnetic resonance imaging of the knee is still a relatively expensive modality.     

Temporal bone imaging

Ameliorated computed tomography techniques and new magnetic resonance sequences have led to an important improvement in temporal bone imaging. Computed tomography is still the method of choice for imaging of temporal bone fractures, middle ear disease, and conductive hearing loss, although magnetic imaging can add important information. Patients with lesions of the cerebellopontine angle; internal auditory canal; inner ear; and, in general, all patients with sensorineural hearing loss, vertigo, and tinnitus are best examined with magnetic resonance imaging. In some cases, however, such as congenital malformations and petrous apex lesions, magnetic resonance imaging and computed tomography are complementary. The value of both modalities is discussed.     

Referral rates and waiting lists: some empirical evidence

This case report describes abnormalities in bilateral rectus capitis posterior minor muscles in one individual with persistent head and neck pain. These findings are muscle atrophy, fatty infiltration on magnetic resonance imaging, and electromyographic abnormalities compatible with denervated muscle. The objective of the study contained herein was to determine if fatty infiltration on magnetic resonance imaging of the rectus capitis posterior minor muscle is the result of disuse or denervation. Electromyography and magnetic resonance imaging data were collected from normal and atrophied muscles. Electromyography and magnetic resonance imaging abnormalities compatible with denervation atrophy were detected. Although we cannot rule out aging or other unknown causes, we suspect that denervation is caused by nerve damage from trauma to the C1 dorsal ramus as a consequence of entrapment within the rectus capitis posterior major muscle.     

MR of the heart under pharmacologic stress

Magnetic resonance imaging is one method for assessing cardiac function and perfusion at rest and under stress conditions. In this article, the potential of stress magnetic resonance imaging for evaluating ischemic heart disease is reviewed, and technical aspects of some developments that may contribute to comprehensive magnetic resonance imaging assessment of heart disease under rest and stress are discussed.     

Comparison of echocardiography with magnetic resonance imaging in the assessment of the athlete's heart

AIM: The purpose of the study was to compare the accuracy of M-mode echocardiography and two different two-dimensional echocardiographic approaches in the assessment of left ventricular mass and volumes in endurance-trained and strength-trained athletes, using magnetic resonance imaging as reference standard. METHODS AND RESULTS: We studied 19 athletes and 10 untrained control subjects, M-mode and two-dimensional echocardiography were compared to magnetic resonance imaging. M-mode echocardiographic left ventricular mass was calculated using the Penn cube convention. Two-dimensional echocardiographic left ventricular mass was calculated using (1) the area-length method as proposed by the American Society of Echocardiography (ASE) and (2) as proposed by Reichek. The best correlation between magnetic resonance imaging and echocardiographic left ventricular mass and volumes was observed with the ASE two-dimensional echocardiographic method. The agreement between them (-3.4 +/- 7.6 g and 18.5 +/- 19.5 ml) was better than between Reichek two-dimensional echocardiography and magnetic resonance imaging (-39.4 +/- 15.4-g and 52.8 +/- 21.7 ml), and demonstrated less random difference than M-mode echocardiography and magnetic resonance imaging (3.2 +/- 21.1 g resp. 15.1 +/- 30.0 ml). CONCLUSION: We conclude that the ASE two-dimensional echocardiographic approach, when using magnetic resonance imaging as a reference standard, was the most accurate estimator of left ventricular mass and volumes in both controls and athletes.     

Magnetic resonance imaging of regenerating and dystrophic mouse muscle

Magnetic resonance imaging allows serial visualization of living muscle. Clinically magnetic resonance imaging would be the first step in selecting a region of interest for assessment of muscle disease state and treatment effects by magnetic resonance spectroscopy. In this study, magnetic resonance imaging was used to follow dystrophy and regeneration in the mdx mouse, a genetic homologue to human Duchenne muscular dystrophy. It was hypothesized that images would distinguish normal control from mdx muscle and that regenerating areas (spontaneous and after an imposed injury) would be evident and evolve over time. T2-weighted images of hind-limb muscles were obtained on anaesthetized mice in a horizontal bore 7.1-T experimental magnet. Magnetic resonance images of mdx muscle appeared heterogeneous in comparison to homogeneous images of control muscle. Foci of high intensity in mdx images corresponded to dystrophic lesions observed in the histologic sections of the same muscles. In addition, it was possible to follow chronologically the extent of injury and repair after an imposed crush injury to mdx muscle. These results should make it possible to obtain meaningful magnetic resonance spectra from particular regions of interest in muscle as viewed in magnetic resonance images (i.e., regenerating, degenerating, normal muscle) acquired during neuromuscular diseases and treatment regimens.