A novel vacuum device for extremity immobilisation during digital angiography: preliminary clinical experiences

Transcription

1 Eur Radiol (2002) 12: DOI /s VASCULAR INTERVENTIONAL R. J. Bale C. Lottersberger M. Vogele A. Prassl B. Czermak A. Dessl R. A. Sweeney P. Waldenberger W. Jaschke A novel vacuum device for extremity immobilisation during digital angiography: preliminary clinical experiences Received: 21 March 2002 Accepted: 4 April 2002 Published online: 1 August 2002 Springer-Verlag 2002 R.J. Bale ( ) C. Lottersberger M. Vogele A. Prassl B. Czermak A. Dessl P. Waldenberger W. Jaschke Department of Radiology, Interdisciplinary Stereotactic Interventionand Planning Laboratory (SIPLab), University of Innsbruck, Anichstrasse 35, 6020 Innsbruck, Austria reto.bale@uibk.ac.at Tel.: Fax: R.A. Sweeney Department of Radiotherapy Radiooncology, University of Innsbruck, Anichstrasse 35, 6020 Innsbruck, Austria Abstract Our objective was to develop and evaluate a non-invasive device for rigid immobilisation during extremity angiography. The patented BodyFix immobilisation device (Medical Intelligence, Schwabmünchen, Germany) consists of a vacuum pump connected to special cushions and a plastic foil that covers the body part to be immobilised. First, the patient s extremity is covered by a thin plastic bag and then wrapped in one of the cushions, placed on the top of the therapy couch, and covered with the plastic foil. The air is evacuated from the cushion under the covering foil by the vacuum pump, resulting a hardening of the cushion and thus immobilisation of the patient s extremity. The rigid immobilisation resulted in a complete absence of motion artefacts in the majority of patients. No pixeling of the images was required in any of the 100 patients vs 32% in the control group. Repetition of series could be avoided in all cases and a substantial increase in the quality of the images was obtained. Setup of the device takes an additional 1 2 min. Vacuum immobilisation allows for comfortable, effective immobilisation during digital subtraction angiography, eliminating motion artefacts. This device has become an indispensable tool in daily clinical routine at our department. Keywords Digital subtraction angiography DSA Extremity Immobilisation Motion artefact Introduction Stable immobilisation of the patient is essential for both diagnostic and therapeutic angiography. Patient movement during angiography is a common source of image degradation artefacts which may result in image interpretation errors [1]. Repetition of sequences, additional administration of contrast media and the associated additional radiation dose to the patient should, however, all be minimised. In addition, movement during therapeutic interventions may increase the risk of complications. In order to avoid the major source of image degradation in digital subtraction angiography (DSA), being motion artefacts, we have developed and modified the BodyFix immobilisation system (Medical Intelligence, Schwabmünchen, Germany; Fig. 1), a non-invasive vacuumbased device for rigid immobilisation of the extremities. Its feasibility and usefulness was evaluated in a prospective study in 100 patients and compared with a control group of 100 patients without BodyFix immobilisation. Materials and methods BodyFix The BodyFix immobilisation device, originally designed for CT and computer-assisted punctures, was modified and adapted to the requirements of DSA. It consists of a vacuum pump connected to different types of machine-washable cushions which are filled with tiny Styrofoam balls (similar to a vacuum splint) and a plastic foil to cover the region of interest. First, the patient s extremity is covered by a thin plastic bag for hygienic reasons. Then, the patient s extremity is wrapped up with one of the cushions, placed

2 2891 Fig. 1a d Setup of BodyFix immobilisation device on the therapy couch. a The patient s extremity, which needs to be immobilised, is covered by a thin plastic bag and placed on one of the cushions. b The patient s extremity is wrapped up with the cushion. c A plastic foil covers the body part to be immobilised. The air is evacuated from between the covering foil and the therapy couch. d The intensity of fixation can be selected by changing the degree of underpressure built up by the vacuum pump on the top of the therapy couch and covered with the plastic foil. The cushions are placed such that there is only minimal separation between the intensifier and object. When the vacuum pump is turned on, the air is evacuated from between the covering foil and the therapy couch, resulting in a hardening of the cushion which is simultaneously sucked against the therapy couch together with the object to be immobilised. This results in immobilisation of the patient s extremity as long as the vacuum persists. The intensity of fixation can be selected by changing the degree of underpressure built up by the vacuum pump. To achieve sufficient immobilisation, the outer plastic foil must be large enough to cover the entire cushion creating a seal to the table. The amount of underpressure used for immobilisation was 80 mbar. Method of DSA Angiography was performed with the Siemens Polystar RD unit (Siemens, Erlangen, Germany). Visipaque 270 (Nycomed Amersham, Oslo, Norway) was used as contrast agent (Fig. 2). For imaging of the iliac arteries contrast agent was applied at 10 ml/s and two images were acquired. For the femoral and the popliteal region contrast agent was applied at 10 ml/s and one image/s was acquired. For the infrapopliteal region 20 ml/s Visipaque 270 was applied and 0.5 images/s were acquired. Patients The feasibility and usefulness of the device was evaluated in a prospective study in 100 patients (73 men, 27 women; age range years, mean age 62 years) and compared with a control group of 100 patients without BodyFix immobilisation (80 men, 20 women; age range years, mean age 64 years). Informed consent was obtained from all patients after the nature of the procedure had been fully explained. Ninety-two patients in the immobilised group and 91 patients in the control group suffered from peripheral arterial disease (PAD stages I III), a total of 8 patients in the immobilised group and 13 patients in the control group suffered from Fontaine stage-iv PAD (Tables 1, 2). The other patients were examined for other diseases including aortic aneurysms (9 patients), Behcet s disease (2 patients) and aneurysms of the iliac arteries (4 patients) or the superficial femoral artery (2 patients; Table 2). The number of sequence repetitions related to motion artefacts and the number of necessary digital pixeling were compared between the two groups. The quality of the resulting images in the iliac, femoral, popliteal and infrapopliteal region were rated by two experienced interventional radiologists by consensus as fol-

3 2892 lows: excellent (bone not visible); very good (only minimal contours of the bone visible); sufficient (sufficient for diagnosis); poor (vessels visible but insufficient for diagnosis); and very poor (vessels not visible). The patients were explicitly asked for any discomfort during the examination. A thorough examination of the immobilised extremity after the procedure was obtained. In 8 of the 100 fixated patients with arterial ulcers in the region of interest, fixation was achieved by draping the foil(s) such that the ulcers were not covered. Results Fig. 2 A 62-year-old man with the diagnosis of peripheral vascular disease IIb of the right leg. Angiography of the iliac and the femoral arteries revealed a severe stenosis of the left external iliac artery and multiple severe stenoses of the right superficial artery (not shown) resulting in a delayed filling of the peripheral arteries; however, due to reliable vacuum immobilisation of the lower limb, image quality was optimal, revealing occlusions of the right tibial artery in the middle of the lower limb (thick arrowhead) and distal occlusions of the left fibular and anterior tibial artery (small arrowheads) Table 1 Image quality in the infrapopliteal region: immobilisation with BodyFix vs control group without immobilisation BodyFix (n=100) Excellent 75 4 Very good Good 0 36 Poor 0 30 Very poor 0 5 Control group (n=100) Thirteen per cent of patients in the fixated arm reported some discomfort, these being patients with Fontaine stage-iii PAD (5 patients) and stage-iv PAD (8 patients). In these patients the underpressure of 80 mbar was only applied during the injections of the contrast media. In the meantime the amount of underpressure was decreased to 20 mbar. In 2 patients with large ulcers, the underpressure could only be increased to 50 mbar which was sufficient to prevent severe motion artefacts. All remaining patients reported no pain or discomfort. A thorough examination of the immobilised extremity after the procedure did not reveal any bruises or swelling directly attributable to the use of the immobilisation device. The device did not interfere with the imaging procedure in any way. The separation of the intensifier from the object was negligible. The time required for set up of the immobilisation device, positioning and fixation of the patient could be reduced to 1 2 min after a short learning phase. Although the system is quite simple, care must nevertheless be taken to create a tight seal between the extremity, the cushion and the therapy couch. Table 2 gives detailed information about the image quality in the iliac, femoral, popliteal and infrapopliteal region depending on the stage of PAD. Due to the absence of motion artefacts in the patients in the fixated group, there was complete absence of bony structures in 75% of the patients in the infrapopliteal, in 46% in the popliteal region, in 68% in the femoral region and in 77% in the iliac region, respectively. Pixeling could be avoided in all 100 fixated patients. In the control group there was complete absence of bony structures in 4% of the patients in the lower limb, in 3% in the popliteal region, in 10% in the femoral region and in 43% in the iliac region, respectively. The series had to be repeated in 21% of the patients. Pixeling had to be performed in 31% of the patients. The initial cost of the system is approximately EUR 5000 while the cost per patient consists of the plastic bag which costs 10 cents per piece. The vacuum device itself can also be used for fixation in MRI, CT [2] and radiotherapy. Discussion In a recent paper Francis et al. [1] have described the reasons for and problems related to motion artefacts during DSA of the lower legs: movement artefacts during

4 2893 Table 2 Image quality in the iliac, femoral, popliteal and infrapopliteal region depending on the stage of peripheral arterial disease (PAD): immobilisation with BodyFix (BF) vs control group without immobilisation Iliac Femoral Popliteal Infrapopliteal BF Control BF Control BF Control BF Control PAD I n=3 n=2 n=3 n=2 n=3 n=2 n=3 n=2 Excellent 2 (66.6) 1 (50) 3 (100) 0 2 (66.6) 0 3 (100) 0 Very good 1 (33.3) 1 (50) 0 1 (50) 1 (33.3) 1 (50) 0 1 (50) Sufficient (50) 0 1 (50) 0 1 (50) Poor PAD II n=69 n=63 n=69 n=63 n=69 n=63 n=69 n=63 Excellent 54 (78.3) 33 (52.4) 51 (73.9) 3 (4.8) 31 (44.9) 2 (3.2) 57 (82.6) 2 (3.2) Very good 11 (15.9) 26 (41.3) 17 (24.6) 55 (87.5) 34 (49.3) 23 (36.5) 12 (17.4) 13 (20.6) Sufficient 4 (5.8) 4 (6.3) 1 (1.5) 3 (4.8) 4 (5.8) 35 (55.6) 0 27 (42.9) Poor (1.6) 0 3 (4.8) 0 18 (28.6) Very poor (1.6) (4.8) PAD III n=12 n=13 n=12 n=13 n=12 n=13 n=12 n=13 Excellent 9 (75) 6 (46.2) 8 (66.7) 3 (23.1) 5 (41.7) 1 (7.7) 6 (50) 0 Very good 2 (16.7) 2 (15.4) 3 (25) 10 (76.9) 7 (58.3) 5 (38.5) 6 (50) 5 (38.5) Sufficient 1 (8.3) 5 (38.5) 1 (8.3) (46.1) 0 3 (23) Poor (7.7) 0 5 (38.5) PAD IV n=8 n=13 n=8 n=13 n=8 n=13 n=8 n=13 Excellent 6 (75) 2 (15.4) 1 (12.5) 0 4 (50) 0 4 (50) 0 Very good 2 (25) 10 (76.9) 5 (62.5) 10 (76.9) 4 (50) 2 (15.4) 4 (50) 4 (30.8) Sufficient 0 1 (7.7) 2 (25) 3 (23.1) 0 10 (76.9) 0 5 (38.4) Poor (7.7) 0 4 (30.8) Others n=8 n=9 n=8 n=9 n=8 n=9 n=8 n=9 Excellent 6 (75) 1 (11.1) 5 (62.5) 4 (44.4) 4 (50) 0 5 (62.5) 2 (22.2) Very good 2 (25) 8 (88.9) 2 (25) 3 (33.3) 4 (50) 2 (22.2) 3 (37.5) 2 (22.2) Sufficient (12.5) 2 (22.2) 0 6 (66.6) 0 0 Poor (11.1) 0 3 (33.3) Very poor (22.2) angiography can be a source of image quality compromise which may in extreme cases lead to either misdiagnoses or, should the examination need to be repeated, increased costs to a department. Frequently encountered sources of motion artefacts are involuntary movements caused by injection of contrast media, especially in the lower limb, uncooperative patients or in prolonged procedures. Since pixel shift compensates for movements in two axes but not for rotations, this technique helps only in selected cases as well as being time-consuming. The ideal fixation system for angiography should grant quick, simple, clean, cheap and effective immobilisation without causing patient discomfort. Many immobilisation devices have been developed, many for radiotherapy [3, 4], each having its own characteristics and drawbacks. For the purposes of imaging, casts and moulds allow for rigid reproducible immobilisation, but they are expensive and time-consuming. We believe that simple, non-invasive devices, such as bandages, foam pillows and sand bags or plastic film [5], are not sufficient for adequate immobilisation. To the authors knowledge, the only system that approaches fulfilment of the aforementioned attributes is one described by Francis et al. [1] who use a 150-µm plastic bag containing polystyrene beads with a lockable valve backed by a filter. The bag is wrapped around the feet and the air is evacuated, causing a partial vacuum to force the beads together. This results in a rigid, translucent fixation, controlling the limb over a large lower limb area. A possible disadvantage of the bag may be that it is slightly bulky which might compromise image quality as well as being of limited use for patients with ulcers. The vacuum technique described above provides quick, effective, safe and comfortable immobilisation of the upper and lower limbs. Vacuum fixation is usually well tolerated by the patients, even over prolonged periods, because of the homogenous pressure applied to the surface of the immobilised body part by the vacuum.

5 2894 Sufficient immobilization may not always be possible due to severe pain related to the ulcers. Unfortunately, we have only limited experience with the application of the BodyFix device in patients with PAD stage IV (8 patients). In these patients fixation was achieved by wrapping the cushions and draping the foil(s) such that the ulcers were not covered. In addition, the extent of underpressure could be adjusted so as to minimize discomfort caused by the procedure. In 2 patients with large ulcers, the underpressure could only be increased to 50 mbar which was sufficient to prevent severe motion artefacts; however, in all the patients in our study with PAD stage IV the image quality in the lower limb was excellent (4 patients) or very good (4 patients). In 5 of 9 patients with PAD stage IV in the control group the image quality was poor (3 patients) or very poor (2 patients). In case of emergency, fixation can be released in numerous ways by both patient and staff: removal of the plastic foil from the table/object immediately reduces the underpressure; a button which can be pushed by the physician allows for quick inflation of air into the vacuum chamber, and, disconnecting the tube from the base plate or the vacuum pump also results in an immediate interruption of vacuum pressure. Our first prototype of this system was described for immobilisation in CT [2]. The system described here, however, is adapted to the requirements of angiography in that the body part is in direct contact with the imaging couch. The base plate previously described would increase the distance between image intensifier and object, cause artefacts, prolong the imaging session and, being large and heavy, cause handling problems. The thin, plastic covering foil does not interfere with an ultrasound beam, so that immobilisation for ultrasound examinations or sonographically guided invasive procedures is also feasible. For surgical or interventional procedures, the area of interest may be covered with selfadhesive sterile plastic foils, thus allowing introduction of surgical instruments or biopsy needles to be introduced without releasing the vacuum. Even if the foil is perforated to accommodate biopsy needles, spare skin lesions, etc., immobilisation is not compromised. Although the foil is quite tear resistant, a tear or leak can be sealed by draping another foil over the leak. Conclusion In conclusion, as extensive experience with our prototype has shown, vacuum immobilisation seems to be a promising method for safe, comfortable and effective immobilisation of the extremities for various purposes, especially for imaging and image-guided interventions. Further investigation on its impact on respiratory, circulatory and other organ functions are necessary before it can be possibly used with a whole-body feature. Current projects include the development of reproducible immobilisation methods by means of casts, foams and vacuum mattresses in combination with the BodyFix device, as well as extending its use to MRI angiography applications, where such a system could also decrease study time and increase patient throughput. Placing the MR coils around an extremity, between skin and covering, is quite possible, providing comfortable and reliable immobilisation in MRI also, requiring the vacuum pump to be shielded or placed outside the scanner room. Financial disclosure Michael Vogele and Reto Bale are co-developers of the BodyFix system and will receive financial returns in case the system is sold. References 1. Francis IS, Dodge GS, Platts AD (1999) The bead bag immobilisation device. Br J Radiol 72: Bale RJ, Vogele M, Rieger M, Buchberger W, Jaschke W (1999) A new vacuum device for extremity immobilisation. Am J Roentgenol 172: Jacobson A, Iversen P, Gadeberg C, Hansen JL, Hjelm-Hansen M (1987) A new system for patient fixation in radiotherapy. Radiother Oncol 8: Gerber RL, Marks JE, Purdy JA (1971) The use of thermal plastics for immobilisation of patients during wide-field radiotherapy. Br J Radiol 44: Greenwood LH, Proto MH, Morse SS (1987) Plastic-wrap restraint for lower extremity arteriography (letter). Am J Roentgenol 149:1082