Extremity Coil Research Articles

Two-dimensional time-of-flight MR angiography of the lower extremities: artifacts and pitfalls.

method for noninvasive imaging of peripheral vascular disease. Two dimensional (2D) time-of-flight (TOF) MR an giography is the most common technique used for evaluation of the pelvic and infrainguinal arteries [11. This pictorial essay presents pit falls and artifacts that may be encountered dur ing clinical MR angiography of the lower extremities. Knowledge of these imaging find ings is essential for accurate interpretation of peripheral 2D TOF MR angiography. MR imaging was performed in a l.5-T Signa scanner (General Electric Medical Systems, Milwaukee, WI). The 2D TOF MR angiograms were acquired in the axial plane in standard body, head, or extremity coils with a spoiled gradient-recalledpulse se quence and flip angles of 45°for the pelvis and 600 for the extremities. The slice thick ness was 2.9 mm and field of view was 32 cm in the body coil; 2.0 mm and 22 cm, re spectively, in the head coil; and 2.0 mm and 16cm, respectively, in the extremity coil. Im aging parameters were TR range/TE range, 29—32/6.7—7.1; first-order gradient moment nulling (flow compensation); tracking infe nor saturation (usually 20 mm below the slice); 256 x 128 matrix; one excitation; and phase encoding from anterior to posterior. Three-dimensional sequences were acquired in the body coil using a fast spoiled gradient recalled or spoiled gradient-recalled pulse se quence; 45_600 flip angle; TR rangeiTE range, 10.6—32/2. 1—6.9; 28—60partitions, 2—2.5mm thick; 36-cm field of view; 256 x 128-256 ma trix; one excitation; and dynamic gadolinium enhancement in all cases [2J. Signal loss in a patent vessel from satura tion of in-plane flow is one of the most com mon pitfalls in 2D TOF MR angiography. When the path of a vesselcausesblood to re

Occlusion of blood flow by high-intensity focused ultrasound

This work investigates the possiblity of occluding blood flow (in vivo) using high-intensity focused ultrasound surgery (FUS). Such an effect could be used, for example, in the noninvasive treatment of foetal dysfunctions. A high-power 1.7-MHz, 150-mm focal length, piezoelectric transducer was used to expose rat femoral vessels to a free field I−SP=4660 W cm−2 for 2 s under terminal anaesthesia. Initially, eight separate exposures were used. Later experiments were aimed at determining an optimal single exposure to produce flow occlusion. Before and after exposure, magnetic resonance FISP 3-D angiograms (MRA) with submillimeter spatial resolution were acquired using a Siemens Vision MR System (1.5T) and extremity coil. In all animals, MRA showed reduced blood flow both in the treated region and distal to it. The results of single-dose optimization will be discussed. The ability to curtail blood flow using FUS allows the possibility of treating Foeto-Foetal Transfusion Syndrome by occluding the placental shunt vessels responsible for vascular inbalance in identical twins. Currently available interventional treatments (surgery or intrauterine laser therapy) have significant mortality and morbidity. The FUS has the advantage of being noninvasive. [Work was funded by the UK Medical Research Council.]

An MR-based technique for quantifying the deformation of articular cartilage during mechanical loading in an intact cadaver joint.

The objective of this study was to develop an MR-based technique for quantifying the deformation of articular cartilage during mechanical loading in an intact cadaver joint at high spatial and temporal resolution. A nonmetallic pressure device was constructed for applying loads of >1000 N to a femoro-patellar articulation within an extremity coil of a clinical 1.5 T MRI scanner. Digital image processing methods were used to determine the location- and time-dependent cartilage deformation in consecutive 2D fat-suppressed FLASH images. Additionally, three-dimensional reconstruction of the cartilage was performed from 3D fat-suppressed FLASH image data. During the first 10 min of static compression, thickness changes between 10 and 30% were observed. Thickness changes greater than 50% and volume changes of 20% were recorded after 3 h. The technique permits analysis of the load and time-dependent mechanical behavior of articular cartilage in its natural environment.

Contrast media-enhanced 3D MR angiography of the peripheral vessels using a "tracking technique": preliminary results

A single bolus contrast-enhanced (CE) 3D MR angiography (MRA) of the peripheral vessels was evaluated using a combination of two surface coils with manual incrementation of the patient table. Fifteen patients with peripheral arterial occlusive disease were examined using an ultrafast CE 3D MRA (TR/ TE/FA 5 ms/2 ms/30 degrees). For imaging of the vessels from the distal aorta to the arteries of the lower limbs a combination of a body-array coil and a flexible extremity coil was applied. A coil-interface was designed for a connection of the two coils. The examinations were performed after a single bolus of 0.15 mmol Gd-DTPA/kg. The tracking technique included a manual incrementation of the patient table and the coil-interface had to be switched from the body-array coil to the flexible extremity coil. For acquisition delay measurement of the MR sequence the individual transit times of the contrast material were detected by using a test bolus. CE 3D MRA was technically successful in 14/15 cases. In one case two vascular segments were not imaged. The qualitative evaluation of all vascular segments documented a high quality without any significant differences between the proximal and the distal arteries (p < 0.05). All hemodynamically significant stenoses (n = 15) and all vessel occlusions (n = 36) were detected. The single bolus CE 3D MRA using a tracking technique is a favourable method in the evaluation of patients with peripheral arterial occlusive disease.

Posterolateral stabilizers of the knee: anatomy and injuries assessed with MR imaging.

T he posterolateral aspect of the knee contains several ligamentous and tendinous structures that are the primary restraints against varus angulation and external rotation of the tibia. These structures are the fibular collateral ligament (FCL), the arcuate ligament, the popliteus tendon, the popliteofibular ligament, and the fabellofibular ligament [1]. Hughston et al. [2] refer to the first three structures collectively as the arcuate complex. In addition to these static stabilizers, dynamic stabilization of the posterolateral corner of the knee is provided by the popliteus, biceps femoris, and lateral gastrocnemius muscles [2]. Injury to the posterolateral structures may lead to posterolateral rotatory instability of the knee, in which the lateral tibial plateau rotates externally and subluxates posteriorly [3]. Acutely, patients may complain of pain in the posterolateral aspect of the knee and chronically may describe the sensation of the knee giving way in extension [1]. Such injuries often accompany anterior cruciate ligament (ACL) and posterior cniciate ligament (PCL) tears [1] but may be subfle and miSsed by the examiner [2]. Clinically unrecognized posterolateral injury has been suggested as a cause of ACL graft failure [4] as well as instability after PCL repair [5]. Materials and Methods We dissected the posterolateral aspect of an embalmed cadaveric knee obtained from our medical school’s department of anatomy. After identifying and photographing the posterolateral ligaments, we coated them with 120% w/v barium paste (E-ZPaste; E-Z-EM, Westbury, NY) and radiographed the specimen using a detail extremity film-screen combination with 6.4 mA and 60 kV. We also reviewed the reports of all MR imaging examinations of the knee peiformed at our institution over a 2-year period, looking forcases ofinjury to the posterolateral Stabilizers. All Studies were performed on l.5-T units (Signa; General Electric Medical Systerm, Milwaukee, WI, or Gyroscan; Philips Medical Systems, Shelton, CI’) using dedicated extremity coils. The routine protocol consisted of sagiual Spinecho Tl-weighted images (TR rangeiTE range, 500600/15-20), gradient-echo T2-weighted images (600-875/15-20; flip angle, 30#{176}), axial spin-echo Ti-weighted images (500-600/15-20), fat-suppressed fast spin-echo 12-weighted images (17004500/50-90; echo train length, eight), and coronal fat-suppressed fast spin-echo proton densityweighted images (1700-3500/18-40; echo train length, eight). Fat suppression was achieved by frequency-selective presaturation on the Signa unit and spectral inversion recovery on the Gymscan unit. Field of view was 16-20 cm and one to two excitetions were performed. Slice thickness for the sagittal and T2-weighted axial sequences was 3 mm, with no interslice gap on the Sigma unit and a gap ofO3 mm on the Gyroscan unit; the slice thickness on the coronal images was 3-4 mm for both units, with no gap on the Signa unit and a gap ofO.3-0.4 mm on the Gyroscan unit. Matrix size was 256 x 192-256 and 205 x 256 for the Signa and Gyroscan units, respectively.

Brain Magnetic Resonance Imaging in Congenital Hypothyroid Infants at Diagnosis

The aim of our study was to investigate the central nervous system (CNS) morphology and myelination with magnetic resonance imaging (MRI) in congenital hypothyroid (CH) infants detected by neonatal screening before replacement therapy. We studied 11 CH infants, 9 girls and 2 boys, mean age 22 days, 3 with aplasia, 5 with ectopia, 2 with hypoplasia of the thyroid gland, 1 with unknown diagnosis. As normal controls 22 term newborns (38 to 41 weeks of gestational age) were studied. MRI studies were performed with a 1.5-T magnet, extremity coil, T1-weighted and heavily T2-sequences axial sections were obtained. No sedation was needed for the MRI studies. MRI brain examination was normal in all patients compared with controls. In particular, no differences in the myelination patterns of the brain were observed between normal subjects and patients with hypothyroidism. Our study shows no morphological brain abnormalities in CH infants detected by neonatal screening before replacement therapy. Perinatal hypothyroidism seems to have no effect on CNS structures.

Magnetic resonance imaging of the musculoskeletal system. Part 5. The wrist.

Musculoskeletal radiology has been transformed with the advent of magnetic resonance imaging. Magnetic resonance imaging provides visualization of the complex anatomy of the wrist and delineation of numerous pathologic processes, which are difficult to visualize with conventional imaging modalities. With the use of sophisticated pulse sequences and a dedicated extremity coil, magnetic resonance imaging allows evaluation of osseous and ligamentous injuries, arthritides, tumors, and tumor-like conditions. Magnetic resonance imaging techniques will be emphasized and anatomy and various pathologic conditions pertaining to the wrist will be reviewed.

Magnetic resonance imaging to study lesions of atherosclerosis in the hyperlipidemic rabbit aorta

We have developed a high resolution magnetic resonance (MR) imaging technique to serially assess lesions of atherosclerosis in a rabbit model. A volume phased array coil was designed and used to image the abdominal aortas of six atherosclerotic rabbits and two age-, sex-, and weight-matched controls. Lesions of atherosclerosis were induced by a combination of repeat balloon injury and a hyperlipidemic diet. All animals were imaged on at least two occasions 9-16 months after initiation of atherosclerosis. In addition, animals were imaged immediately after sacrifice. Anatomic dissection and histology were performed to verify the MR findings. The volume phased array coil improves the image signal-to-noise ratio over existing extremity coils and resulted in higher resolution images of the abdominal aorta. Proton density-weighted images acquired with 2D/3D fast spin-echo are the most useful sequence to outline the vessel wall and to differentiate wall from lumen and background. Progressive wall thickening and lumen stenosis were observed in the serial images of the diseased rabbits. Wall thickness and lumen area derived noninvasively from the in vivo MR images correlate with postmortem MR images and sections of aorta examined by dissection microscopy and histology. Spin-echo and fast spin-echo imaging with a phased array body coil can be used to accurately assess plaque dimensions, and potentially can be used to image intraplaque features and to monitor lesion progression or regression. It should also be possible to adapt these techniques to assess human disease, especially for peripheral vascular problems.

Lower extremities: MR angiography with a unilateral telescopic phased-array coil.

In a comparison of conventional and magnetic resonance (MR) angiography of the lower extremities, MR imaging was performed with extremity and body coils and a unilateral six-coil telescopic phased-array coil. In one of seven volunteers, average signal-to-noise ratio was 140% higher with the latter (p < .01), only three of five stations were necessary, and examination time was decreased 50%. In the four patients, correlation in findings was 100%.

MRT der Kniegelenke jugendlicher Fußballspieler

In a prospective study, the right knee of 21 symptom free juvenile footballers was examined by MRT (group I) and the results were compared with 12 juveniles of similar age but who did not take part in any special sporting activities (group II). A 1.5 Tesla Magnetome with an extremity coil was used. There were no abnormal changes in either group in the cruciate ligaments. The hyaline cartilage medially was about 10% thicker than laterally in both groups but in group I it was, on average, 24.8% thicker than in group II. Increased signals in the centre of the menisci were observed in 8 members of group I and two in group II. 5 of the 8 in group I, but none in group II, also showed an increase in the joint fluid.

Magnetic Resonance Imaging of Postmortem Infant Brains

In order to obtain postmortem magnetic resonance images of infant brains, the formalin-fixed brains of 37 infants, ranging in age from 17 days to 17 months, were studied. Factors that improved scan resolution included formalin fixation, not washing the formalin from the brain, imaging the brain with a thin film of water over it, and the use of an extremity coil. The scan resolution was of sufficient quality to direct the histopathologist to regions requiring microscopic examination and to map the progress of myelination.

BRAIN MRI IN CONGENITAL HYPOTHYROID INFANTS AT DIAGNOSIS

Cerebral atrophy with sella turcica alterations have been found in adult patients with primary hypothyroidism, who started replacement therapy after one year of age. Only one report described demyelinating processes in a 14 months old untreated girl, that presented a development delay.The aim of our study was to investigate the CNS morphology and myelination with Magnetic Resonance Images (MRI) in congenital hypothyroidism (CH) detected by neonatal screening before replacement therapy.We studied 7 CH infants, 5 girls and 2 boys, mean age 21 days, 4 agenetic and 3 ectopic. Beclard's nucleus was absent in 2 patients, mean T4 concentration at diagnosis was 22.2 ng/mL (n.v.: 50-115 ng/mL), As normal controls 22 term newborns (38-41 weeks of gestational age) were studied.MRI studies were performed with a 1.5 T magnet, extremity coil, T1 - weighted and heavily T2 - sequences. In all patients and controls a complete set of T1 and T2 - weighted axial sections were obtained. No sedation was needed for the MRI studies.Brain MRI examination was normal in all patients compared to controls. In particular no differences in the myelination patterns of the brain were observed between normal subjects and patients with hypothyroidism. The ventricles and the subarachnoid spaces showed a normal size.Our study shows no morphologic brain abnormalities in CH infants delected by neonatal screening before replacement therapy. Perinatal hypothyroidism seems to have no effect on CNS structures.

The ulnar tunnel at the wrist (Guyon's canal): normal MR anatomy and variants.

The ulnar tunnel (Guyon's canal) is a fibroosseous tunnel along the anteromedial portion of the wrist that contains the ulnar nerve and artery. As with the adjacent carpal tunnel, its main clinical significance is that it may cause nerve compression. The purpose of this study was to determine whether the anatomy of this area could be depicted in sufficient detail by MR imaging for MR to be useful in the evaluation of patients with ulnar neuropathy. MR studies of 36 wrists of volunteers were reviewed with attention to the size and shape of the canal, its anatomic boundaries, the presence of anomalous muscles, the size and bifurcation of the ulnar nerve, and the presence of a fibrous or muscular arch overlying the deep motor branch of the ulnar nerve. T1-weighted transverse MR images of 3-mm-thick sections were obtained by using either an extremity coil or dedicated wrist coil. Excellent anatomic delineation was achieved. The boundaries and shape of the canal varied from proximal to distal, but no statistical differences were present in the mean cross-sectional area of the canal. Anomalous muscles were present in the canal in nine (25%) of 36 wrists; six (67%) of the nine were bilateral. The ulnar nerve had a mean diameter of 3 mm and bifurcated an average distance of 12 mm from the proximal margin of the pisiform bone. Delineation of the fibromuscular arch at the origin of the flexor digiti minimi brevis muscle was limited by imager resolution, but 50% were judged to be fibrous and 50% to be muscular. Our results show that MR images depict the ulnar tunnel in excellent detail. Since those structures associated with ulnar neuropathy are clearly delineated by MR, the procedure should be useful in the evaluation of patients suspected of having ulnar nerve compression within the tunnel.

Do asymptomatic marathon runners have an increased prevalence of meniscal abnormalities? An MR study of the knee in 23 volunteers.

Excessive repetitive musculoskeletal loads and stresses associated with intense physical activity may lead to deterioration of the menisci of the knee. Therefore, MR imaging was performed on the knees of 23 asymptomatic marathon runners (eight men, 15 women; average age, 40 years; average number of years training, 10; average training distance per week, 41 miles) to determine the prevalence of meniscal signal abnormalities. None of the runners had previous knee injuries or surgery and each of them regularly competes in 26-mile, 50-mile, or 100-mile marathon races. T1-weighted coronal MR images and proton density-weighted and T2-weighted sagittal images were obtained with a 1.5-T MR system and a transmit/receive extremity coil. The medial and lateral menisci were divided into four portions, or horns, and a total of 92 horns were evaluated (i.e., four horns per knee: medial posterior, medial anterior, lateral posterior, and lateral anterior). Two meniscal horns (2%) had grade 3 signal (grade 3 indicates a meniscal tear), 12 (13%) had grade 2 signal, 29 (32%) had grade 1 signal (grades 1 and 2 are indicative of meniscal degeneration), and 49 (53%) had grade 0 signal (grade 0 is normal). Overall, the prevalence of meniscal tears was 9% (two meniscal tears found in 23 runners). This is lower than the prevalence of MR signal abnormalities indicative of meniscal tears reported for asymptomatic, nonrunner athletes (20% of 20 athletes) and for asymptomatic nonathletes (16% of 74 subjects). Fifty-three percent of the meniscal horns of the nonrunner athletes had grade 1 or 2 signal, indicative of meniscal degeneration. Our results indicate that the prevalence of meniscal tears in marathon runners is no higher than the prevalence reported for sedentary persons, and the runners have the same amount of meniscal degeneration as do nonrunner athletes.

A design for a double-tuned birdcage coil for use in an integrated MRI/MRS examination

The performance of a new design for a double-tuned birdcage volume coil using multiple-pole tuning elements was evaluated. The relative signal to noise of a double-tuned four-strut extremity coil (22 cm long, 15 cm diameter) was compared with that of two single-tuned extremity coils of the same dimensions. The signal to noise of the double-tuned extremity coil at the 1H frequency was 92 ± 3% of that obtained with the single-tuned proton coil. The signal-to-noise ratio obtained with the double-tuned coil at the 31P frequency was 94 ± 4% of the signal to noise obtained with the single-tuned 31P Coil. The signal-to-noise comparisons between the extremity coils show that the double-tuned design is competitive with single-tuned coils of similar design at both frequencies and may actually make possible images and spectra with superior signal to noise to that obtainable with single-tuned coils in an integrated exam. These preliminary experiments show that this new design has advantages over single-tuned coils for generating spatially localized 31P spectra. This dual capability offers clear advantages for the integration of MRI and MRS in the clinical setting.

4845431 Variable aperture, variable frequency extremity coil for magnetic resonance imaging

The present invention pertains to an extremity coil for magnetic resonance imaging. The extremity coil includes means for varying the aperture of the coil, and means for supporting the coil. Additionally, the extremity coil can include means for varying the resonant frequency of the coil.

Meniscal and ganglion cysts of the knee: MR evaluation.

Meniscal and ganglion cysts frequently present as palpable masses of the knee but occur at different locations than do popliteal cysts. Meniscal cysts also may be discovered incidentally on studies performed for suspected internal derangement. Sixteen cystic lesions of the knee were evaluated with MR, including 11 meniscal cysts and five ganglion cysts. Scans were performed at 1.5 T by using a transmit/receive extremity coil or a receive-only surface coil. Standard spin-echo imaging, including at least one long-TR/asymmetric-TE sequence, was performed in all cases. In six patients, gradient-echo, reduced flip-angle sequences also were done. All meniscal cysts (but none of the ganglion cysts) were associated with horizontal meniscal tears. Cysts were visualized best on the long-TR/TE images; meniscal tears were seen best on the short-TR/TE and long-TR/short-TE images. Meniscal tears and cysts were also seen well on the fast-scanning sequences. Septations were noted in four meniscal cysts and in four ganglion cysts on the long-TR/TE images. Long-TR/TE images were also useful in showing the relationship between the cyst and joint capsule in three of the ganglion cysts. MR imaging is an effective, noninvasive method for evaluating cystic lesions of the knee. Meniscal cysts are always associated with underlying horizontal meniscal tears, which can be detected with MR. Ganglion cysts are not associated with meniscal tears, but may have connections to the joint capsule, which can be detected with MR.