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The objective of this study was to demonstrate in an animal model the feasibility of a passive tracking technique for catheter visualization of magnetic resonance (MR)-guided endovascular procedures. All experiments were performed in a 0.2 Tesla open MR system. Susceptibility-based catheters and guide wires were introduced into the aorta and were advanced selectively into the splenic and renal arteries under MR guidance. Based on a previously acquired contrast-enhanced magnetic resonance angiography (MRA) data set, the catheter positioning was performed by using a single-slice true fast imaging with steady state precession (FISP) sequence with a frame rate of 1.3 seconds. Contrast-enhanced MRA was performed in all animals. All catheters were advanced without complications into the aorta and were introduced into the proximal parts of the right renal and splenic arteries under MR guidance. Catheter manipulations were more difficult in the distal parts of these vessels due to the more complex anatomy. Passive catheter tracking is a valuable and technically robust alternative to active tracking methods, because it does not require additional hardware and, thus, can be implemented and used easily with any open MR imaging system. J. Magn. Reson. Imaging 1999;10:841-844., (Copyright 1999 Wiley-Liss, Inc.)

Purpose: The aim of this study is to introduce a fast, T2 weighted true FISP keyhole sequence implemented on an open C arm low field magnetic resonance (MR) scanner for interventional procedure guidance., Method: Following the acquisition of a reference data set using a true FISP (fast Imaging with Steady Precision) sequence, only the 32 central raw data lines (keyhole) are acquired in a fluoroscopic-like mode enabling continuous image reconstruction and update. The keyhole true-FISP sequence was tested in animal experiments and used in MR-guided interventions in 10 patients., Results: The described true FISP keyhole sequence is characterized by an image frame rate of 2.5 images per second and a T2-like contrast. Due to system constraints with respect to the reconstruction, the actual displaying of images was delayed by up to 180 ms., Conclusions: The use of the described keyhole sequence enabled a fluoroscopy-like guidance of interventional devices in an open, low-field system.

Purpose: An animal model is used to investigate whether MR angiography combined with super-paramagnetic particles of iron oxide (SPIO) is suitable for detecting thromboses., Methods: 42 rats in groups of 7 each were examined on days 1, 3, 5, 7, 9 and 11, respectively, after mechanical/chemical thrombus induction in a 1.5 Tesla magnet with a FISP sequence (TR/TE/FA 50 ms/6 ms/40 degrees). Imaging was performed before and up to 90 minutes after intravenous injection of 30 mumol FE/kg BW of the experimental SPIO (hydrodynamic diameter, 34 +/- 17 nm LLS; R1 and R2 relaxivity at 0.47 T, 31 and 57 L/(mmol*s)). MIP reconstructions of MR angiographies were submitted to consensus assessment by two examiners. using histology as the gold standard., Results: The image quality of MIP reconstructions was rated as good in 38 of 42 cases. With regard to thrombotic vessel occlusion, MR angiography coincided with histology in 17 of 42 cases and differed in 25, lumen narrowing being overestimated by MRI in 4 cases and underestimated in 21. In these 21 cases, the histologically observed recanalization could not be detected by MR angiography., Conclusions: SPIO-enhanced MR angiography achieves adequate vessel contrast and reliable thrombus detection in animal experiments. Partial volume effects prevent microscopically observed recanalization from being detected by clinical MRI.

Purpose: The use of mini-laparoscopy scissors to remove a central venous catheter inadvertently fixed to the wall of the brachiocephalic vein is described., Patient and Methods: During a rethoracotomy in a 15-year-old female patient, a central venous catheter preoperatively introduced in the left subclavian vein was inadvertently trapped by a suture and fixed to the wall of the left brachiocephalic vein. The foreign body was removed by use of a transjugularly introduced venous sheath, a catheter wire snare, and mini-laparoscopy scissors., Results: The fixed catheter was freed from the wall of the vein under fluoroscopic control with the help of a mini-laparoscopy scissors. Since the intravasal end of the catheter had already been grasped during mobilization with the wire snare it could be completely removed subsequently without any problem., Conclusions: The percutaneous, intravascular use of mini-laparoscopy instruments may be considered for foreign body removal in special cases.

Purpose: To investigate interactive MR-assisted bile duct drainage in pigs with the passive visualization technique using near real-time imaging., Methods: 8 bile duct drainages were placed in an open low-field MR system (0.2 Tesla) in 4 pigs with surgically induced cholestasis. After planning the intervention with magnetic resonance cholangiography (MRC), both the puncture and catheter placement were interactively guided using a fast T2-weighted true FISP sequence., Results: MRC enabled interventional planning in all puncture attempts. Punctures were unproblematic in all attempts, the bile ducts were punctured 6 times after the first and twice after the second attempt. Placement of the passively visible catheter was successful in all animals. The applied sequence enables interactive fluoroscopy-like positioning of the devices., Conclusion: The procedure introduced here enables reliable and fast placement of a bile duct drainage in an animal model using a low-field MR system.

Purpose: To investigate the use of magnetic resonance (MR) imaging to guide interstitial laser therapy of deep hemangiomas and vascular malformations in children., Materials and Methods: Sixteen children aged 3 months to 16 years with symptomatic vascular lesions underwent percutaneous laser treatment. MR imaging guidance of the laser applicator and online thermomonitoring with MR imaging were performed with a 0.2-T open MR system. Follow-up studies were performed 2 days and 6 weeks after thermotherapy., Results: Interactive positioning of the laser applicator was possible in all patients. Online thermomonitoring was possible in 122 of 137 therapy spots (89%). There was a good correlation between volumes of coagulated tissue on intraprocedural T1-weighted images and volumes of coagulated tissue on follow-up T2-weighted images. At 6-week follow-up, MR imaging demonstrated a reduction in lesion size in 10 patients (mean reduction, 72%) and an increase in lesion size in two patients (mean increase, 134%). Clinical symptoms improved in 14 of 16 patients (88%)., Conclusion: MR imaging-guided laser therapy appears to be a safe and potentially effective minimally invasive treatment for selected children with vascular lesions.

Objective: To study magnetic resonance (MR) imaging pattern of normal hyaline articular cartilage in the knee joint with regard to the contribution of the "magic angle" effect to the MR signal., Design: Thirty-two healthy volunteers were imaged in a standard supine position in a 1.5-T unit using spin echo and gradient echo sequences. Nine volunteers were reimaged with the knee flexed. The signal behavior of the hyaline cartilage of the femoral condyles was evaluated qualitatively and quantitatively. The extended and flexed positions of the nine volunteers were compared., Results: A superficial and a deep hyperintense layer and a hypointense middle cartilage layer were observed. Segments of increased signal intensity were visible along the condyles; a magic angle effect on signal intensity was evident in the hypointense middle layer with both gradient echo and spin echo images., Conclusion: The MR signal behavior of hyaline cartilage is influenced by the alignment of the collagen fibers within the cartilage in relation to the magnetic field. Failure to recognize this effect may lead to inaccurate diagnosis.

The tools and devices used for patient treatment during interventional procedures must be accurately and safely localized. Recently, procedure guidance has been performed increasingly with MRI, but tool localization has been performed primarily by analyzing the lack of signal caused by displaced excited tissue and/or susceptibility artifacts. In this investigation, a new technique was developed to actively detect and visualize interventional tools using receive coils mounted on the tip of the interventional devices. Unlike earlier methods, in which images from small device-mounted coils are super-imposed on a previously acquired image data set, our localization method uses similar tip-mounted tools in combination with a radiofrequency (RF) switching circuit, standard imaging coils, and specially modified sequences to toggle between the standard and tip-mounted receive coil within a single fluoroscopic mode sequence. With this technique, the misregistration between the reported anatomic location and true location of interventional devices is minimized.

Background and Objective: Interstitial laser therapy (ILT) is a minimally invasive treatment method for congenital vascular malformations (CVM). This study was intended to show whether or not open magnetic resonance imaging (MRI) offers a means of on-line thermometry and procedure control., Study Design/patients and Methods: ILT using a bare fiber and an Nd:YAG laser was applied in 20 children with CVM under open MR control., Results: With the open MR systems, needle placement and advancement was excellent in all cases. On-line thermometry was possible in 90% of the therapy spots. The 6 week MR follow-up revealed a 76% reduction in tumor size in 14 patients. Clinical symptoms improved in 85% of the patients., Conclusion: MR-guided ILT could become a safe method to treat selected types or selected regions of CVM.

Aim: To evaluate MR cholangio-pancreatography (MRCP) using an open low magnetic field apparatus in normals and in patients with mechanical cholestasis., Methods: MRCP was performed on five normals and on 30 patients, using both an 0.2 Tesla and 1.5 Tesla apparatus. With the low field system, rapid acquisition by relaxation enhancement was used, for the high field system, half Fourier acquisition single shot turbo spin-echo sequences were used. In all patients, sonography and ERCP or PTC was performed; 23 underwent surgery., Results: In all normals it was possible to show the bile duct, hepatic duct, gall bladder and intrahepatic ducts of the first order. Using the high field system, second order ducts could be shown and sometimes third order ducts. In the patients, MRCP, using either system, demonstrated all 21 obstructive sites due to tumours or stenoses. Stones were shown in 69% by the low field system and in 88% by the high field system., Conclusion: MRCP can be successfully carried out using the low field system. In the presence of mechanical cholestasis, image quality is adequate for the localisation of stenoses and occlusions, and, using an open magnet, is suitable for planning further intervention.

Purpose: Development of a percutaneously implantable catheter system for regional chemotherapy of liver metastases and its application in patients with surgically implanted but dislocated catheters., Methods: Thirty-three patients with liver metastases of colorectal tumors were submitted to percutaneous puncture of the subclavian artery and insertion of a catheter whose tip was placed in the proper hepatic artery and whose end was subcutaneously connected with an infusion pump., Results: The mean duration of therapy via the percutaneously inserted catheter was 27 weeks (+/-14 weeks). The most frequent complication was disconnection of the therapy catheter from the tube of the infusion pump. Eighty percent of all complications were corrected by reintervention. The therapy drop-out rate due to catheter-associated complications was 9%., Conclusion: Percutaneous insertion of a catheter for regional chemotherapy of the liver is a relatively uncomplicated method with high patient acceptance and simple access for reintervention.

Color duplex sonography (CDS) is primarily applied as a diagnostic procedure. It has not yet established itself as an aid in punctures or other interventions. The aim of this study was to evaluate the value of CDS in arterial and venous vascular punctures. One hundred and sixty-five CDS-assisted vascular punctures were performed in a prospective study after three unsuccessful palpation-guided vasopunctures or in the absence of a palpable pulse. All CDS-assisted punctures were successful. The duration of each attempted puncture showed no statistically significant difference compared with the palpation-guided puncture technique. In the cases with three unsuccessful palpation-guided vascular punctures, the CDS-assisted technique was successful after 1.66 attempts on the average. It is concluded that CDS-assisted vascular puncture is a fast and safe alternative for puncturing a pulseless vessel or for puncturing under difficult conditions.

Iodine-containing contrast agents are currently used for angiography. However, due to the relatively low atomic number of iodine, imaging must be performed with a relatively low tube voltage. Gadolinium has been used for several years as a contrast agent in MRI with low adverse side effects. This substance has a higher atomic number as compared with iodine. We investigated whether the use of a gadolinium-containing contrast agent with a higher tube voltage reduces the radiation exposure in angiography, and how the image quality compares with the previous technique. A total of 15 patients were examined with either a survey angiography or a selective angiography. In all patients angiography was performed with an iodine-containing contrast agent with a tube voltage of 75 kV. Then gadolinium-containing contrast agent was administered immediately with a tube voltage of 110 kV. Radiation exposure and image quality were compared. On average, a dose reduction factor of 3.57 times was achieved by using 110 instead of 75 kV. However, the image quality was poorer in the majority of cases as compared with the images taken with iodine as a contrast agent and a tube voltage of 75 kV. The poorer image quality is caused by the relative low concentration (0.5 M) of the used gadolinium solution. A 1 M solution is currently tested for market approval and would probably solve this problem.

Sport-associated knee-joint alterations are frequent. A correct and rapid differentiation between traumatic lesions, chronic degenerative changes, and adaptive processes is important with regard to therapy as well as training and competitive planning for athletes. After the case history and physical examination, X-ray images are an absolute necessity for more in-depth diagnostic procedures. Depending on the clinical symptoms, partial aspects of the knee-joint can be visualized by sonography as well as by conventional tomography and computed tomography. If, however, a comprehensive evaluation of all knee-joint structures is needed, magnetic resonance imaging of the knee-joint should be performed. As a rapid, noninvasive procedure with high diagnostic reliability for all essential knee-joint structures only magnetic resonance imaging presently fulfills the specific demands placed on a modern diagnostic procedure by doctors working in sports-medicine.

Unlabelled: The aim of this prospective MRI study was the analysis of the post-operative signals derived from two techniques for cruciate ligament reconstruction., Patients and Methods: Group 1 consisted of 15 patients who had undergone conventional plastic repair by patellar tendon transplant and group 2 was made up of 15 patients with arthroscopic reconstruction with semitendinosus grafts. They were examined at 6 weeks and 6 months post-operatively., Results: Typical appearances of normal transplants were found in 19 patients. After 6 months 8 of the patellar tendon transplants and three of the semitendinosus transplants could not be clearly defined. At this time there was a significant increase in signal intensity in the middle third of the transplant in group 1., Conclusion: Bearing in mind the different operative techniques, there was a higher impingement rate in group 1. The post-operative MRI findings at 6 months after surgery allowed differentiation between pathological changes (impingement) and revascularisation (remodelling).

The aim of this study was to demonstrate metabolic changes in the small joints of the hand due to rheumatoid arthritis by means of 31-phosphorus spectroscopy. Suitable measurements were developed and 11 normals and 12 patients were then examined during the course of treatment. Relative concentration of low energy phosphorus metabolites was increased in arthritic joints. The phospholipid quotient (phosphomonoester/phosphodiester) and the relationship of inorganic phosphate and beta-nucleoside triphosphate were significant factors during the course of individual treatments.

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.

Meniscus tears were experimentally produced by surgery in 5 pigs. They were identified via MR tomography with the selected routine sequence (SE: TR 1600, TE 22/80 msec, SD 3 mm) independent of position, orientation and severity. The best imaging was obtained between the 2nd and 8th weeks after the operation in the sagittal plane. Subsequently the contrast and with it simultaneously the delineation between intact fibrous cartilage and rupture cleft decreased; this could be observed in sequences weighted according to proton density and T2 in different degrees of intensity. Parallel to this a trial to induce degeneration in the meniscus tissue resulted 8 weeks after the operation in central, signal-intensive zones in the menisci. No success was achieved in trying to improve imaging of the pathological changes by means of intraarticular injections of Gd-DTPA; this was tried out at various points of time. Besides enabling the imaging of lesions of the fibrous cartilage as a matter of principle, MR tomography can also give limited information on the age of a meniscus tear.

As a reproducible, painless and non-invasive method magnetic resonance imaging is helpful in the diagnosis of meniscus-lesions. In 35 cases of 39 examined knees the MR findings corresponded to findings at arthroscopy; 12 of the 35 patients had a meniscal lesion.

58 knee joints of 57 patients were examined via magnetic resonance tomography. Measurements were effected at 1.5 tesla using SE sequences in multilayer and dual-echo technique. Arthroscopic reference findings were available from all patients, comparison between arthroscopy and MRT in 93 menisci resulted in the present patient group in a negative predictive value of 97.4% and in a positive predictive value of 88.6%. Degenerative changes of the rupture-free menisci could be diagnosed via MRT in 15 cases. Besides the frequently observed central degeneration there were also superficial degenerations and fibrovascular proliferations. MRT can be recommended for pre-arthroscopy screening in suspected meniscus lesions on the basis of the methods of measurement and evaluation presented in this paper.