Magnetic resonance safety update 2002: implants and devices

The preservation of a safe magnetic resonance (MR) environment requires constant vigilance by MR healthcare professionals, particularly with regard to the management of patients with metallic biomedical implants or devices. The variety and complexity of implants and devices constantly changes, requiring continuous attention and diligence with regard to obtaining the most current and accurate information about these objects relative to the MR environment. This review article discusses MR safety and MR compatibility issues and presents important information for a variety of implants and devices, with an emphasis on those objects that have recently undergone evaluation or that require additional consideration because of existing controversy or confusion.     

Magnetic resonance imaging of the elbow

With the current popularity of racket and throwing sports, the number of individuals seeking medical care for elbow pain and dysfunction has increased. Elbow dysfunction may be related to acute or chronic injury to the soft tissue or osseous components of the elbow. With magnetic resonance imaging (MRI), it is now possible to accurately determine the nature and extent of the pathological changes in ligaments, tendons, muscles, and osseous structures of the elbow joint. This information facilitates the choice of the appropriate therapeutic regimen.     

Magnetic resonance imaging artifacts produced by dental implants with different geometries

Objectives:The purpose of this study was to evaluate the MRI-artifact pattern produced by titanium and zirconia dental implants with different geometries (diameter and height).Methods:Three titanium (Titan SLA, Straumann) and three zirconia (Pure Ceramic Implant, Straumann) dental implants differing on their design (diameter x height) were installed in porcine bone samples. Samples were scanned with a MRI (3T, T1W turbo spin echo sequence, TR/TE 25/3.5ms, voxel size 0.22×0.22×0.50 mm, scan time 11:18). Micro-CT was used as control group (80kV, 125mA, voxel size 16µm). Artifacts’ distribution was measured at vestibular and lingual sites, mesial and distal sites, and at the apex. Statistical analysis was performed with Within-ANOVA (p=0.05).Results:Artifacts distribution measured 2.57 ± 1.09 mm for titanium artifacts and 0.37 ± 0.20 mm for zirconia artifacts (p<0.05). Neither the measured sites (p=0.73) nor the implant geometries (p=0.43) influenced the appearance of artifacts.Conclusion:Artifacts were higher for titanium than zirconia implants. The artifacts pattern was similar for different dental implant geometries.     

Magnetic resonance imaging in pediatric elbow fractures

Purpose: Magnetic resonance imaging (MRI) evaluation of pediatric elbow trauma with or without a visible fracture on radiography.

Material and Methods: MRI was performed in the acute phase in 25 children with an elbow injury. Nine patients with an elbow effusion only on radiographs and 16 with a fracture or luxation seen on radiographs underwent subsequent MRI. No sedation was used.

Results: MRI revealed eight occult fractures (89%) in seven out of nine patients who had only an effusion on radiographs. Based on MRI findings, septic arthritis was suspected in one patient. Two patients out of five with a supracondylar fracture on the radiograph had a cartilage lesion in the humerus. MRI depicted a 3-mm gap on the articular surface in two patients with a lateral condyle fracture, a more accurate fracture location in two patients than the radiographs, and an additional occult fracture in two patients. MRI showed a fracture not seen on radiographs in two of three patients with prior luxation.

Conclusion: MRI is a sensitive and accurate method in the diagnosis of pediatric elbow injuries, especially when only an effusion is present on radiographs. Occult fractures are more common in pediatric patients with elbow injury than reported earlier.     

Magnetic resonance imaging ofthe hand and wrist — clinical significance and impact

The clinical experience with magnetic resonance imaging (MRI) in the evaluation of the hand and wrist has beenrapidly expanding over the past few years. The use of dedicated surface coils has improved the ability of MRI to assess the soft tissue and osseous structures in this region. The evaluation of the patient with chronic hand and wrist pain can be a diagnostic dilemma. The anatomic complexity of the hand and wrist makes the pathological possibilities innumerable, ranging from tenosynovitis to osteonecrosis. MRI is invaluable in the detection of avascular necrosis of the carpus, and allows staging, determination of prognosis, and assessment of treatment. Carpal instability can be evaluated by this noninvasive modality, which provides information regarding ligament integrity as well as an assessment of'the articular surface. More recent application in the upper extremity has allowed the determination of flexor tendon integrity, and MR angiography can be used in the evaluation of vascular disorders of the hand. MRI has made a significant impact in our assessment and treatment of these various disorders of the hand and wrist. As the techniques are further refined, we can expect continued improvement in our diagnostic capabilities.     

Magnetic resonance imaging of knee trauma

This article reviews the magnetic resonance (MR) appearance of normal knee anatomy and the role of MRI in the evaluation of knee trauma. Images acquired in the sagittal plane are the most useful. A combination of T₁- and T₂-weighted spin echo pulse sequences is most commonly employed. A meniscal tear is identified by an intrameniscal signal which extends to the joint surface. MR and arthroscopic findings agree in more than 90% of patients. It is important to be familiar with the MRI appearance of normal anatomic variants that may be confused with meniscal tears: the transverse geniculate ligament, the hiatus of the popliteal tendon sheath, and the meniscofemoral ligaments. Tears in the anterior cruciate, posterior cruciate, and collateral ligaments are also depicted.The following article is one in a series of review articles which represent expansions of papers presented at the annual meeting of the International Skeletal Society and were solicited by the editors     

Magnetic resonance imaging of the feto-placentar unit after fetoscopic laser coagulation for twin-to-twin transfusion syndrome

Twin-to-twin transfusion syndrome (TTTS) is a severe complication in monochorionic twin pregnancies that results from a hemodynamical imbalance of placentar vascular anstomoses that connect the circulation of both fetuses. In TTTS, a poly/oligohydramnios sequence with high fetal morbidity and mortality rates occurs. Fetoscopic laser coagulation of the placentar anastomoses can limit or prevent fetal injury. The purpose of this report is to present and discuss fetal magnetic resonance imaging as a postoperative imaging tool after fetoscopic laser coagulation.     

Magnetic resonance imaging (MRI) of diastematomyelia

Summary The MRI-features of diastematomyelia in a patient with unusually late onset of symptoms are reported. Direct visualization of the split cord and low conus on frontal MR-images was facilitated by three-dimensional Fourier transform (3-DFT) image acquisition.     

Magnetic resonance imaging of themusculoskeletal system

The accuracy of magnetic resonance imaging (MRI) in evaluating disorders of the musculoskeletal system is wellestablished. MRI is especially valuable in evaluating pathology of the major joints and soft tissues of the body. Importantly, MRI is a noninvasive technology. As with any new technology in medicine, time is required to establish the place of the technology in the armamentarium of clinicians. This is the unsettled situation MRI finds itself in today.     

Magnetic resonance imaging findings of extrapelvic endometriosis of the round ligament

A 31-year-old woman presented with a mass in her groin accompanied by intense pain during the menstrual period. A poorly circumscribed, elastic, hard mass was palpable in her right inguinal region. Magnetic resonance imaging showed that the mass had continuity with the inguinal course of the round ligament of the uterus. The mass lesion was well enhanced with high intensity on diffusion-weighted imaging. An operation was performed, and the histological diagnosis was endometriosis of the round ligament. After operation, she was completely relieved of pain. It is important to include endometriosis in the differential diagnosis in women with painful inguinal mass lesions at risk for endometriosis.     

Magnetic resonance imaging of truama patterns in the knee

This review describes how knee trauma results in recognizable patterns of soft tissue and osseous injury. The features of these injuries on magnetic resonance imaging are described, and examples are presented. Recognition of these magnetic resonance patterns of knee trauma will help the radiologist more accurately diagnose the type and extent of knee injuries.     

Magnetic resonance imaging of posttraumatic soft tissue disorders

The applications of magnetic resonance imaging with regard to musculoskeletal disorders have continued to expand over the past decade. It is considered to be the preferred imaging method for evaluation of soft tissue processes owing to its marked sensitivity to signal alterations in abnormal tissue, and it is capable of performing this function equally well in processes that affect the muscle, connective tissue, or subcutaneous tissue. In this pictorial essay, a review of many common posttraumatic soft tissue disorders and their characteristic magnetic resonance features, as well as some of the advantages of this imaging method, will be discussed.     

Magnetic resonance (MR) differential diagnosis of breast tumors using apparent diffusion coefficient (ADC) on 1.5‐T

To review the published reports concerning the apparent diffusion coefficient (ADC) value evaluation for the differentiation between malignant and benign breast tumors, articles were searched with the inclusion criteria: (a) a 1.5‐T unit was used; (b) the diagnostic criteria were clearly stated; (c) diffusion‐weighted images (DWIs) were obtained, and ADC value was calculated; (d) ADC values of breast tumors were reported with mean ± standard deviation (SD). Meta‐analysis from 12 articles revealed that the pooled sensitivity and specificity were 0.89 (95% confidence interval [CI], 0.85–0.91) and 0.77 (95% CI, 0.69–0.84), respectively, and that only the maximum b factor correlated with the mean ADC values of malignant and benign tumors, and the noncancerous breast tissue (P< 0.05,P < 0.01,P< 0.05, respectively). In conclusion, ADC evaluation is useful for the differentiation between malignant and benign breast tumors. J. Magn. Reson. Imaging 2009;30:249–255. © 2009 Wiley‐Liss, Inc.     

Magnetic resonance imaging findings of vulvar epithelioid sarcoma

We describe here a case of vulvar epithelioid sarcoma. Epithelioid sarcoma is a malignant appendicular skin tumor that is rarely of vulvar origin. Magnetic resonance imaging (MRI) revealed a solid mass with an ulcer-like lesion and multilobulated contour. To our knowledge, this is the first case of vulvar epithelioid sarcoma described in the MRI literature.     

Magnetic resonance safety testing of a newly-developed fiber-optic cardiac pacing lead

PURPOSE: To assess magnetic resonance (MR) safety for a newly developed, fiber-optic cardiac pacing lead. MATERIALS AND METHODS: MR safety was assessed for the fiber-optic cardiac pacing lead by evaluating magnetic field interactions and heating. Translational attraction and torque were evaluated using a 1.5-Tesla MR system and previously described, standardized techniques. MR imaging-related heating was assessed using a 1.5-Tesla MR system and a transmit/receive, body radiofrequency (RF) coil with the fiber-optic lead positioned to simulate an in vivo condition in a saline-filled phantom. The phantom had dimensions similar to a human subject's torso and head. A fluoroptic thermometry system was used to record temperatures on and near the electrodes of the fiber-optic pacing lead at five-second intervals immediately before and during 20 minutes of MR imaging performed at a whole-body-averaged specific absorption rate (SAR) of 1.5 W/kg. Temperatures were also recorded from a reference site during this experiment. RESULTS: Magnetic field interactions for the fiber-optic lead were minimal (deflection angle, 23 degrees; torque, +2). The highest temperature change recorded for the fiber-optic cardiac pacing lead and reference site was +0.8 degrees C. CONCLUSION: The minor magnetic field interactions and relative lack of heating for the fiber-optic pacing lead indicate that it should be safe for patients with this device to undergo MR imaging procedures using MR systems operating at 1.5-T or less and at a whole-body-averaged SARs up to 1.5 W/kg.     

Morphological manifestations of nonpuerperal mastitis on magnetic resonance imaging

Purpose:

To investigate the morphological features of nonpuerperal mastitis on magnetic resonance imaging (MRI).

Materials and Methods:

MRI results of 27 patients diagnosed with nonpuerperal mastitis were retrospectively analyzed according to the Breast Imaging Reporting and Data System (BI‐RADS).

Results:

According to the enhanced MRI results, 22 cases presented as nonmass‐like enhancements and five cases presented as masses. For the 22 nonmass‐like enhancement lesions, one case showed as a homogeneous enhancement and 21 cases showed as heterogeneous enhancements. In the 21 heterogeneous enhancement cases, 13 contained lesions of rim‐like enhancement. With regard to the number of lesions with rim‐like enhancement, 11 presented as multiple and two as single. In the five mass lesions, three presented as rim enhancements. Indications of rim or rim‐like enhancement accounted for 59% (16/27) of all cases. For the 16 cases that presented with signs of rim or rim‐like enhancement, the central hypointensity area surrounded by enhanced rim or rim‐like entity showed as hyperintensity in 14 cases and hypointensity or heterointensity in two cases on T2‐weighted imaging.

Conclusion:

On contrast‐enhanced MRI, most nonpuerperal mastitis presented as nonmass‐like lesion with heterogeneous signal intensity. The observation of signs of rim or rim‐like enhancement on contrast‐enhanced MRI with central hypointensity areas showing as hyperintensity on T2‐weighted imaging is suggestive of the possibility of nonpuerperal mastitis. J. Magn. Reson. Imaging 2011;33:1369–1374. © 2011 Wiley‐Liss, Inc.     

Magnetic resonance imaging near metal implants

The desire to apply magnetic resonance imaging (MRI) techniques in the vicinity of embedded metallic hardware is increasing. The soft-tissue contrast available with MR techniques is advantageous in diagnosing complications near an increasing variety of MR-safe metallic hardware. Near such hardware, the spatial encoding mechanisms utilized in conventional MRI methods are often severely compromised. Mitigating these encoding difficulties has been the focus of numerous research investigations over the past two decades. Such approaches include view-angle tilting, short echo-time projection reconstruction acquisitions, single-point imaging, prepolarized MRI, and postprocessing image correction. Various technical advances have also enabled the recent development of two alternative approaches that have shown promising clinical potential. Here, the physical principals and proposed solutions to the problem of MRI near embedded metal are discussed.