Hans Peter Ledermann

Blood Oxygenation Level–Dependent Magnetic Resonance Imaging of the Skeletal Muscle in Patients With Peripheral Arterial Occlusive Disease

Background— Blood oxygenation level–dependent (BOLD) magnetic resonance imaging (MRI) has been used to measure T2* changes in skeletal muscle tissue of healthy volunteers. The BOLD effect is assumed to primarily reflect changes in blood oxygenation at the tissue level. We compared the calf muscle BOLD response of patients with peripheral arterial occlusive disease (PAOD) to that of an age-matched non-PAOD group during postischemic reactive hyperemia. Methods and Results— PAOD patients (n=17) with symptoms of intermittent calf claudication and an age-matched non-PAOD group (n=11) underwent T2*-weighted single-shot multiecho planar imaging on a whole-body magnetic resonance scanner at 1.5 T. Muscle BOLD MRI of the calf was performed during reactive hyperemia provoked by a cuff-compression paradigm. T2* maps were generated with an automated fitting procedure. Maximal T2* change (&Dgr;T2*max) and time to peak to reach &Dgr;T2*max for gastrocnemius, soleus, tibial anterior, and peroneal muscle were evaluated. Compared with the non-PAOD group, patients revealed significantly lower &Dgr;T2*max-values, with a mean of 7.3±5.3% versus 13.1±5.6% (P<0.001), and significantly delayed time-to-peak values, with a mean of 109.3±79.3 versus 32.2±13.3 seconds (P<0.001). Conclusions— T2* time courses of the muscle BOLD MRI signal during postocclusive reactive hyperemia revealed statistically significant differences in the key parameters (&Dgr;T2*max; time to peak) in PAOD patients compared with age-matched non-PAOD controls.

Work-up of the diabetic foot

Diabetes is a common disease with potentially devastating complications affecting the foot and ankle. A combination of vascular disease, peripheral neuropathy, and immunopathy results in a cascade of conditions including ischemia and infarction, tendinopathy, atrophy, edema, deformity, neuropathic osteoarthropathy, callus, ulceration, and infection. MRI is useful for evaluation of these complications, and assists the clinician in medical or surgical planning.

Chronic post-traumatic osteomyelitis of the lower extremity: comparison of magnetic resonance imaging and combined bone scintigraphy/immunoscintigraphy with radiolabelled monoclonal antigranulocyte antibodies

Abstract Objective. A retrospective study of the validity of combined bone scintigraphy (BS) and immunoscintigraphy (IS) using 99mTc-labelled murine antigranulocyte antibodies (MAB) and magnetic resonance imaging (MRI) in chronic post- traumatic osteomyelitis. Design and patients. The results of MRI and combined BS/IS of 19 lesions in 18 patients (13 men, 5 women; mean age 45 years, range 27–65 years) were independently evaluated by two radiologists and one nuclear medicine physician with regard to bone infection activity and extent. The patient group was a highly selective collection of clinical cases: the average number of operations conducted because of relapsing infection was eight (range 2–27), the average time interval between the last surgical intervention and the present study was 6.5 years (range 3 months to 39 years), and from the first operation was 14 years (range 1.5–42 years). Interobserver agreement on MRI was measured by kappa statistics. Sensitivity, specificity, accuracy, positive predictive value (PPV) and negative predictive value (NPV) were calculated for MRI and the nuclear medicine studies. Results. For MRI/nuclear medicine, a sensitivity of 100%/77%, a specificity of 60%/50%, an accuracy of 79%/61%, a PPV of 69%/58% and a NPV of 100%/71% were calculated. Four MR examinations were false positives because of postsurgical granulation tissue. A high degree of interobserver agreement was found on MRI (κ=0.88). A low-grade infection was missed on two scintigrams, while four were false positive because of ectopic haematopoietic bone marrow, and in one examination the anatomical distortion resulted in an inaccurate assignment of the uptake leading to false positive findings. Image analysis was frequently hindered by susceptibility artefacts due to residual abrasions of metallic implants after removal of orthopaedic devices (15/18 patients); this led to limited assessment in 17% (3/18 patients). Conclusion. Acute activity in a chronic osteomyelitis can be excluded with high probability if the MRI findings are negative. In the first postoperative year fibrovascular scar cannot be distinguished accurately from reactivated infection on MRI and scintigraphy may improve the accuracy of diagnosis. MRI is more sensitive in low-grade infection during the later course than combined BS/IS. Scintigraphic errors due to ectopic, peripheral, haematopoietic bone marrow can be corrected by MRI.

Pitfalls and limitations of magnetic resonance imaging in chronic posttraumatic osteomyelitis.

Abstract. The aim of this study was to evaluate pitfalls and technical limitations of MR imaging in diagnosing relapse of chronic posttraumatic osteomyelitis of the lower extremities. Retrospective analysis of MR examinations in 15 patients (17 body areas) with suspected relapse of chronic posttraumatic osteomyelitis (at least 1.5 years duration/mean number of surgical procedures per patient: 5.8). The MRI findings were compared with postoperative bacteriology (n = 11) and clinical follow-up (n = 4). Five patients had additional CT examination. Magnetic resonance imaging identified all infected areas correctly, but five uninfected regions were diagnosed false positive due to postoperative scarring/oedema in bone defects (n = 4) and soft tissue (n = 1). Specificity of MRI in diagnosing active bone infection was 63 % and sensitivity 100 %. Additional CT was preoperatively necessary in 5 patients (33 %) to further examine osteomyelitic and reparative bone remodeling. Metal artefacts were present in 11 patients, rendering complete evaluation impossible (n = 2) or considerably more difficult (n = 4). Scarring/oedema in postoperative bone defects occurs up to 13 months postoperatively and represents a major pitfall leading to low specificity. Definitive evaluation of suspected fistula, bony fragments and mineralization by MRI may be limited in this special patient group and requires additional CT in one third of patients. Metal artefacts occur in most patients and may impair or even prevent correct film evaluation in 23 and 11 %, respectively.

MRI of Hepatic Adenomatosis: Initial Observations with Gadoxetic Acid Contrast Agent in Three Patients

OBJECTIVE The purpose of our study was to describe the MR signal characteristics of histologically proven liver adenomatosis in three patients using gadoxetic acid, a newly developed liver-specific MR contrast agent. CONCLUSION In all three patients, more than 100 liver adenomas revealed no metabolism of the new liver-specific contrast agent in the delayed phase. Because of absent or strongly reduced intracellular uptake of gadoxetic acid in all adenomas during delayed contrast-enhanced series, differentiation of adenomas from dysplastic or malignant lesions was not possible.