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Original Report |
1 Ludwig Boltzmann Institute of Interventional Magnetic Resonance at the Department of Radiology, AKH St. Pölten, Propst Führer Str. 4, A-3100 St. Pölten, Austria.
Received February 14, 2000;
accepted after revision December 14, 2000.
Address correspondence to E. Salomonowitz.
Abstract
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CONCLUSION. The mean duration of a biopsy was 21 min; there were no major complications. Image contrast, signal, matrix options, and visibility of needle track and tip position permitted uncomplicated orientation. The interventional MR technique could be applied in any puncture setting.
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A large number of procedures were spinal applications; approximately 50% of punctures (n = 180) were performed for periradicular pain therapy and facet joint blockades, and 50% (n = 181) for biopsies of thoracic, abdominal, and vertebral focal lesions. To my knowledge, this report presents the largest series of routine single-center clinical implementation of the same MR technique for all interventions.
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The study was approved by the hospital institutional review board. To prevent bias in selection, patients were randomly assigned to CT, MR imaging, or sonographic imaging for the punctures, according to room availability at the time of registration. The randomization was altered for patients with pacemakers, aneurysm clips, or other materials that might be adversely influenced by the MR imaging environment; for those who expressed possible claustrophobia; and for obese patients, who were assigned to CT. Within the same time period, 343 punctures were performed with sonographic or CT guidance.
Of the 250 patients, appointments for 148 were scheduled between 7:00 A.M. and 11:00 A.M., 83 between 11:00 A.M. and 3:00 P.M., and only 19 after 3:00 P.M., although the department provided the hospital with a 24-hr MR imaging facility. All patients who underwent the procedure were fully informed and had consented to the intervention. All 361 punctures in the study were carried out personally by the author. Obtaining informed consent and patient aftercare were performed jointly by the author with other physicians and MR radiographers.
After the settings on the equipment were adjusted, each biopsy was performed only once for standardization purposes. A single puncture was made and was registered as such in the statistics. Of the 361 biopsies under MR imaging guidance, 67% were performed transversely from ventral, lateral, or dorsal approaches. The remaining 33% were performed obliquely or double-angled in the triangulation technique because one of the main advantages of MR-guided puncture is the opportunity it affords to perform oblique puncture and thus avoid crucial structures [1].
The 361 targets included lung lesions (n = 16) (Fig. 1A,1B,1C,1D); lymph nodes of the mediastinum (n = 4); lesions in all eight segments of the liver (n = 42); tumors in the gallbladder bed (n = 4); lymph nodes in the hilum of the liver (n = 6); pathologic enlargements in the head of the pancreas (n = 17); tumors in the body or tail of the pancreas (n = 7); space-occupying masses in the hilum of the spleen (n = 2); tumors of the mesentery (n = 8); retroperitoneal paraaortic lymph nodes (n = 31); lymph nodes within the hilum of a kidney (n = 5); kidney tumors (n = 8); inguinal lymph nodes (n = 10); presacral space-occupying masses (n = 5); paraspinal tumor L4 (n = 3); thoracic, lumbar, and sacral vertebrae (n = 9) (Fig. 2A,2B,2C,2D); intervertebral disks TH 7/8 and TH 8/9 (n = 4); intervertebral joint blockades (n = 37); and periradicular pain therapy at L4 (n = 39), L5 (n = 63), and S1 (n = 41).
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A 1.5-T standard MR imaging system (Gyroscan ACS-NT; Philips, Best, The Netherlands) was used, in the beginning with PowerTrak 1000, and then with PowerTrak 6000 gradient systems. The releases R 4.5 to R 6.2.1 were employed without additional technical equipment or special interventional design. The duration of the biopsy was measured from the start of the localizing sequence to the time of the patient's departure from the investigation room. The time taken to inform, prepare, and position the patient, and the duration of aftercare were not taken into account because this time varied widely from patient to patient.
All of the instruments used were made from titanium (Somatex, Berlin, Germany), 15- to 23-gauge in diameter, and 9-15 cm in length. In five instances, the coarseness of the tissue or bone necessitated the application of an 18-gauge steel biopsy needle (Surecut; TSK, Tochigi, Japan) in addition to the Somatex needle. They were used in tandem technique, beside and parallel to each other, with the titanium needle serving as a guide, because steel produces a huge artifact and completely distorts the MR image. These additional Surecut biopsies were not included in the statistics.
The interventional MR biopsy technique is shown in Figures 1A,1B,1C,1D and 2A,2B,2C,2D. The patient was partially wheeled out of the magnetic isocenter after each step and wheeled in again for the next step. IV contrast material was not administered, but 2 mL of 1:50 diluted gadopentetate dimeglumine (Magnevist; Schering, Berlin, Germany) was administered if appropriate, especially during periradicular infiltrations, to check the position of the needle tip and thereby avoid the risk of thecal sac intravasation when applying the therapeutic agent. In all patients, 1% lidocaine (Xylanaest Purum; Gebro, Fieberbrunn, Austria) was used locally. In addition, IV injection of midazolam (Dormicum; Hoffmann-LaRoche, Basel, Switzerland) was used for conscious sedation in three patients.
Step 1 of the biopsy technique consisted of positioning the patient and marking the target region with a self-made localization grid that used vitamin E pellets placed at a predefined distance to one another, and obtaining the localizing sequence, a T2-weighted fast (turbo) spin-echo sequence, as an overview. The following parameters were used: TR/TE, 1800/100; alpha, 90°; number of signals averaged, 4; field of view, 430 mm; matrix, 2562; rectangular field of view, 80%; number of slices, 15; slice thickness, 10.0 mm; gap, 1.0 mm; bandwidth, maximum possible frequency (water—fat shift minimal); time of acquisition, 1 min 33 sec.
Step 2 consisted of correcting the patient's position if necessary, and measuring the second sequence using a Tl-weighted fast gradient-echo (turbo field-echo) with suspended respiration (Fig. 1A,1B,1C,1D). We used the following turbo field-echo parameters: TR/TE, 12/4; alpha, 60°; number of signals averaged, 2; field of view, 400 mm; matrix 2562; rectangular field of view, 80%; number of slices, 29; slice thickness, 2.0 mm; gap, 0.2 mm; bandwidth, maximum possible frequency (water—fat shift minimal); time of acquisition, 16 sec. If additional T2 information was required at this step, a short turbo spin-echo sequence was included as described in step 4 (Fig. 2A,2B,2C,2D).
In step 3, the access was traced and defined according to the localization grid, followed by the actual biopsy (marking, washing, allowing the cleaning solution to take effect, covering, administering local anesthesia, making an incision if necessary, and advancing the needle into the selected position). Then the position of the needle was documented in two perpendicular planes (Fig. 1A,1B,1C,1D) with the purpose of seeing the tip of the needle anterior to the intended site of biopsy.
Step 4 consisted of a consecutive aspiration or cutting (in this report, in 181 instances), or application of a therapeutic agent (180 instances). Then the final control sequence was measured, which was a T2-weighted turbo spin-echo similar to that performed in the beginning but shorter and with thinner slices. In this step, we used the following parameters: TR/TE, 1500/100; alpha, 90°; number of signals averaged, 3; field of view, 400 mm; matrix, 2562; rectangular field of view, 80%; number of slices, 11; slice thickness, 6.0 mm; gap, 0.6 mm; bandwidth, maximum possible frequency (water—fat shift minimal); time of acquisition, 54 sec.
The cytologic or histologic specimens were immersed in a 3.8% sodium citrate solution and forwarded to the pathology department. For a comparative cost analysis, method-related investments (i.e., specialty construction, hardware, software, training, furniture, and costs of financing), consumable articles, and costs of concomitant pre- and postoperative diagnoses and therapy were documented or retrieved retrospectively from the controlling department.
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The needle was selected in each case in accordance with the patient's level of obesity, the purpose of the investigation, and the target organ. The most commonly used needle size was 19.5-gauge (42%, aspiration only), followed by 18-gauge (31%, aspiration or cutting biopsy). In more than 85% of the punctures, a 12-cm-long needle was used. In none of the interventions was the gantry too narrow or the needle too long. The needle tip positions were proven and documented by contrast injections (2 mL of 1:50 gadopentetate dimeglumine solution) for each of the 180 pain-therapy cases. Correction of the needle position was required in 33 instances (18.3%).
The needle was visible as a hypointense structure, the size of which depended on the susceptibility artifact it produced. Artifact size decreased with spin-echo (as opposed to gradient-echo) imaging, stronger gradients (thinner slices), and larger receiver bandwidth. Artifact size increased with increasing TE and voxel size. For instrument visualization, orientation of the z-axis, the size of the biopsy needle, frequency-encoding direction, and sequence design were the most important parameters. If the orientation of the needle was at various angles and not parallel to the magnetic field, the needle was invariably visualized with misregistration artifacts. Instruments made from titanium were depicted with a roughly threefold increase in diameter, and the tip of a needle was pseudopropagated by a discrete distance as a result of the so-called dipole artifact [2,3,4]. Misregistration of the needle tip was taken into account when the procedure was planned.
An average of seven sequences were measured in this series of 361 punctures. The entire puncture procedure, as described, took 12-46 min (average, 21 min). None of the biopsies resulted in intercurrent major complications. In no instance did the closed magnet hinder use of the chosen direction and access. Sedation was required for only three patients. Minor complications included local hemorrhage (liver and lung, n = 5) and pneumothorax (n = 8, three of which were detected on a CT follow-up scan obtained 2 hr after MR imaging and were not visible on the expiratory chest radiograph).
According to the department of controlling at the hospital, the mean cost of one CT scan is $80 U.S. and that of one MR imaging examination is $267 U.S. when only the costs of equipment are taken into account. When the entire expense of legal regulations, hospital specifications, and personnel is taken into account, the costs are almost equivalent for the two modalities (sonography costs much less). These expenses include building maintenance, safety measures, legal representation, availability, and hold-out crew capacity. The costs of the equipment itself constitute a small portion of the overall costs. The costs of consumption articles for the different interventional modalities are also essentially equal, amounting to approximately $60 U.S. for an average titanium, steel aspiration biopsy, or sonographic reflecting needle.
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The titanium needles used during the study were continuously improved. The appearance and feel of a titanium needle are remarkably different from that of a steel needle. Although titanium is, by its nature, a metal, it is soft and pliable—more like plastic than metal. Because of a stellate pattern of the molecular structure, titanium surfaces are not smooth; they are raw and coarse, do not traverse tissue freely, and may not be guided with one hand. Treatment of the needle surfaces made it possible to handle the material more easily. The expense of an instrument made from titanium more or less matches the price of a steel needle, and seemingly adapts to local market requirements. Incidentally, calculations of the total costs of a complete investigation include not only the basic needle purchase, but also the overhead costs, including storage and replacement of articles with expiration dates, and the costs of disposal of used needles— currently a major issue.
Interventional MR imaging has the advantage of being able to reveal lesions that are either not visible or poorly visible on sonography or CT [7]. In addition, MR imaging provides several planes of documentation, an advantage in planning and executing interventions. On the other hand, working in the magnet room requires specific training; for example, a steel scalpel blade for skin incision must be held forcefully. By the nature of spatial encoding, the needle tip will be misregistered in the form of a discrete anterior feed. The monitor may show image distortion due to magnetic flux lines. Therefore, the operator must take into account the specific features of the MR imaging environment.
In this study, the relatively consistent brevity of the interventions made it possible to perform MR investigations without obstructing work flow, even at times of heavy workload. This is of utmost importance to radiologists and others in health care and academic settings who must conform to increasingly rigid economic restraints to be both efficient and effective.
In the quest for the "ultimate interventional MR indication," a further goal of the study was to determine whether that which is achieved with other modalities can also be achieved by means of MR imaging, initially without considering which method is least expensive. Costs of method-related investments, disposable biopsy equipment, and perioperative conduct (e.g., CT after lung biopsy) were evaluated. In the context of cost analyses and economic restrictions, interventional MR imaging compares well with other targeted procedures, including CT [8].
The biopsy sequences used in this study were selected with the intention of performing the procedures as speedily as possible. Real-time sequences [3, 5, 9] did not provide perceivable advantages; with "needle-watching," the puncture process became too slow. It was important to have a strong gradient system enhancing image quality [10]. Holding one's breath for 10-15 sec is close to the physical limit for an individual in poor health.
In the course of the 3 years this study spanned, substantial advances were made in MR imaging equipment [11, 12]. Therefore, this study was concluded by performing the 361 biopsies and punctures by the described technique. The investigation protocols described have now been changed to T2-weighted "ultrashort" turbo spin-echo (with cut edges of echo for acquisition shortening) and three-dimensional breath-hold Tl-weighted turbo field-echo maximum gradient power sequences, preferably with the use of the body coil for freedom of movement. Spin-echo parameters are TR shortest/TE, 3661/100; alpha, 90°; turbo spin-echo factor (echo train length), 49; profile order, linear, number of signals averaged, 4; field of view, 430 mm; matrix, 2562; rectangular field of view, 80%; number of slices, 15; slice thickness, 6.0 mm; gap, 0.6 mm; water—fat shift, maximum; time of acquisition, 1 min 27 sec. Gradient-echo parameters are shortest TR/TE, 8.2/4; alpha, 40°; shot interval, shortest; half scan; three-dimensional order, YZ; inverting prepulse with shortest delay; T1-contrast enhancement; number of signals averaged, 2; field of view, 400 mm; matrix, 2562; rectangular field of view, 80%; number of overcontiguous slices, 13; slice thickness, 2.0 mm; gap, -1.0 mm; water—fat shift, maximum; time of acquisition, 11 sec.
A single person performed these biopsies; the learning curve would be a few months for radiologists not well versed in this technique. Subsequent to this study, the technique has been mastered at our institution and the experience gained has resulted in routine MR interventions that would not have been possible a few years ago, including biopsies of the bone and breast (using a dedicated apparatus), and an entire morning of pain therapy every week. We recommend CT for lung biopsy because we have a high rate of pneumothoraces; otherwise, for reasons of standardization and for practical purposes, we do not alter the interventional MR technique according to the biopsied lesion site.
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