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The purpose of this study was to evaluate the feasibility of MRI guidance for percutaneous retrograde drilling in the treatment of osteochondritis dissecans of the talus (OCDT). Four patients, one juvenile and three adults, with one OCDT lesion each and persisting ankle pain after conservative treatment, were treated with MRI-guided retrograde drilling. All lesions were stable and located in the middle or posterior medial third of the talar dome. Pain relief and the ability to return to normal activities were assessed during clinical follow-up. MRI and plain film radiographs were used for imaging follow-up. Technical success was 100 % with no complications and with no damage to the overlying cartilage. All patients experienced some clinical benefit, although only one had complete resolution of pain and one had a relapse leading to surgical treatment. Changes in the pathological imaging findings were mostly very slight during the follow-up period. MRI guidance seems accurate, safe and technically feasible for retrograde drilling of OCDT. Larger series are needed to reliably assess its clinical value. • MRI serves as a useful guidance method for numerous mini-invasive applications. • Retrograde drilling is a cartilage-sparing alternative in the treatment of osteochondritis dissecans. • MRI guidance seems feasible for treatment of osteochondritis dissecans of the talus.

The purpose of this study was to evaluate the technical feasibility of MR-guided percutaneous breast biopsy (LCNB) and breast hook wire marking in a low-field (0.23 T) MRI system with optical instrument tracking. MR-guided core biopsy and/or hook wire marking was performed on 13 lesions observable at MR imaging only. Seven breast LCNBs and 10 hook wire markings were performed under MR guidance on 11 patients. The diagnosis was confirmed by excision biopsy or mastectomy in 12 lesions and with histopathological and cytological diagnosis and 12-month clinical follow-up in one lesion. All lesions seen in the high-field scanner were also successfully identified and targeted in the low-field scanner. The following procedures were typically technically successful. There were difficulties due to unsatisfactory functioning of some core biopsy guns. Detailed description of low-field MR guidance and optical tracking in breast biopsies is provided. The procedure seems accurate and safe and provides means to obtain a histological diagnosis of a breast lesion only seen with MRI. The low-field biopsy system is comparable to the high-field MRI system. MR-compatible biopsy guns need to be improved.

The purpose of this study was to analyze the costs of magnetic resonance imaging (MRI)-guided laser ablation and to compare them with the costs of surgery in the treatment of osteoid osteoma. Seven patients with osteoid osteoma were treated with MRI-guided interstitial laser ablation during 1 year. The reference material consisted of six patients whose osteoid osteoma was treated surgically by either superficial or deep excision with metallic fixation. The costs were analyzed by using activity-based cost accounting. The mean cost of the MRI-guided laser ablation was 2,392 euros and of the excision of superficially located osteoid osteoma 1,807 euros. The cost of excision of deeply located osteoma with metallic fixation was considerably higher (4,996 euros). This was due to the higher material, personnel, and ward costs. The cost of MRI-guided laser ablation of osteoid osteoma was higher than the cost of surgical excision of a superficial osteoma but considerably lower than the cost of excision of a deeply located osteoma where metallic fixation was needed. When the number and mean cost of sick days or days of restricted weight bearing were also included, the cost of MRI-guided laser ablation was lower than the costs of either superficial or deep excision.

The purpose of this study was to test the hypothesis that when ultrasound (US) guidance is not feasible, abdominal biopsies can be performed safely and accurately under magnetic resonance imaging (MRI) guidance in a low-field environment. MRI-guided abdominal biopsy was performed on 31 consecutive patients, in whom US-guided abdominal biopsy was not possible because the lesion was not visualized in US (n=27) or an US-guided procedure was not considered safe (n=4). The locations of the lesions were liver (n=14), pancreas (n=6), lymph node (n=4), retroperitoneal mass (n=3), adrenal gland (n=3) and spleen (n=1). The average size of the lesion was 2.2 cm (range 1-4 cm) in maximum diameter. All procedures were done by using a 0.23-T open-configuration C-arm-shaped MRI scanner with interventional optical tracking equipment and software. Fine-needle aspiration (FNA) biopsy was performed on all 31 patients; 18 patients underwent both FNA biopsy and cutting needle core biopsy. Procedures were evaluated for diagnostic sensitivity, specificity and accuracy as well as procedure time and complications. The FNA biopsy specimens were adequate for interpretation in 27 (87%) of 31 cases. Two of these proved to be false-negative findings during follow-up or subsequent biopsy. The final diagnosis was malignant in 15 and benign in 16 patients. The sensitivity, specificity and accuracy of FNA biopsy were 71, 100 and 81%, respectively. Of the 18 core-needle biopsies, one was determined false-negative owing to nonrepresentativeness. The sensitivity, specificity and accuracy of histological samples were 90, 100 and 94%, respectively. The needle time was 19 min on average and the mean room time was 1 h 48 min. No immediate or late complications occurred. MRI-guided abdominal biopsy can be performed safely and accurately in a low-field environment in patients for whom an US-guided procedure is not feasible.

The aim of this study was to analyze and compare the costs of low-field (0.23 T) MRI- and CT-guided bone biopsies. The cost comparison consisted of 18 MRI-guided and 12 CT-guided bone biopsies performed during a 1-year period. The costs and activities of these two methods were analyzed by using activity-based cost accounting (ABC). The costs of MRI-guided bone biopsy (1205 Euro) were 2.55-fold compared with those of the CT-guided bone biopsy (472 Euro). The higher costs of the biopsy procedure in MRI were due to the higher material (5.57-fold) and personnel (2.73-fold) costs. The MRI-guided bone biopsies proved to be considerably more expensive than CT-guided bone biopsies. This was due to the higher material costs, especially the highly priced MRI compatible instrumentation and the longer procedure time. The MRI guidance in performing bone biopsies should be justified on the basis of the better accuracy and the lack of radiation. Evaluations of cost-effectiveness concerning MRI-guided bone biopsy are needed.

The purpose of this study was to determine the feasibility and features of low-field MR imaging in performing interstitial laser ablation of osteoid osteomas. Between September 2001 and April 2002, five consecutive patients with clinical and imaging findings suggesting osteoid osteoma and referred for removal of osteoid osteoma were treated with interstitial laser treatment. A low-field open-configuration MRI scanner (0.23 T, Outlook Proview, Philips Medical Systems, Finland) with optical instrument guidance hardware and software was used. Laser device used was of ND-Yag type (Fibertom medilas, Dornier Medizin Technik, Germany). A bare laser fiber (Dornier Medizin Technik, Germany) with a diameter of 400 microm was used. Completely balanced steady-state (CBASS; true fast imaging with steady precession) imaging was used for lesion localization, instrument guidance, and thermal monitoring. A 14-G (Cook Medical, USA) bone biopsy drill was used for initial approach. Laser treatment was conducted through the biopsy canal. All the lesions were successfully localized, targeted, and treated under MRI guidance. All the patients were symptom free 3 weeks and 3 months after the treatment. There was one recurrence reported during follow-up (6 months). The MRI-guided percutaneous interstitial laser ablation of osteoid osteomas seems to be a feasible treatment mode.

The purpose of this study was to evaluate the feasibility of MRI-guided bone biopsy with optical instrument tracking and evaluate advantage of combined fine-needle aspiration (FNA) with trephine biopsy. Twenty trephine bone biopsies and 13 FNAs were performed under MRI and CT guidance in 14 patients. Informed consent was obtained from all patients. The evaluation of diagnostic accuracy was achieved by comparing the histopathological and cytological diagnosis with current or final diagnosis made during 6-month clinical follow-up. A 0.23-T open MRI scanner with interventional tools (Outlook Proview, Marconi Medical Systems, Cleveland, Ohio) was used. A surface coil was used. For trephine biopsy MRI-compatible bone biopsy set (Daum medical, Schwerin, Germany) was used. The FNA was performed with MRI compatible 20-G needle (Cook, Bloomington, Ind.). The diagnostic accuracy of MRI-guided trephine biopsy was 95%. The FNA sample diagnosis concurred with the histological in 54%. Our results show that MRI guidance in bone biopsies is accurate and safe. It is comparable to CT-guided or open biopsy. The role of combined FNA with bone biopsies remains controversial.