Lisa Zipp

Clinical implications of skeletal muscle blood-oxygenation-level-dependent (BOLD) MRI

Blood-oxygenation-level-dependent (BOLD) contrast in magnetic resonance (MR) imaging of skeletal muscle mainly depends on changes of oxygen saturation in the microcirculation. In recent years, an increasing number of studies have evaluated the clinical relevance of skeletal muscle BOLD MR imaging in vascular diseases, such as peripheral arterial occlusive disease, diabetes mellitus, and chronic compartment syndrome. BOLD imaging combines the advantages of MR imaging, i.e., high spatial resolution, no exposure to ionizing radiation, with functional information of local microvascular perfusion. Due to intrinsic contrast provoked via changes in hemoglobin oxygen saturation, it is a safe and easy applicable procedure on standard whole-body MR devices. Therefore, BOLD MR imaging of skeletal muscle is a potential new diagnostic tool in the clinical evaluation of vascular, inflammatory, and muscular pathologies. Our review focuses on the current evidence concerning the use of BOLD MR imaging of skeletal muscle under pathological conditions and highlights ways for future clinical and scientific applications.

Blood oxygenation level-dependent (BOLD) MRI of human skeletal muscle at 1.5 and 3 T

To evaluate the dependence of skeletal muscle blood oxygenation level‐dependent (BOLD) effect and time course characteristics on magnetic field strength in healthy volunteers using an ischemia/reactive hyperemia paradigm.

Effects of Covert and Overt Paradigms in Clinical Language fMRI

RATIONALE AND OBJECTIVES The aim of this study was to assess the intrasubject and intersubject reproducibility of functional magnetic resonance imaging (fMRI) language paradigms on language localization and lateralization. MATERIALS AND METHODS Fourteen healthy volunteers were enrolled prospectively and underwent language fMRI using visually triggered covert and overt sentence generation (SG) and word generation (WG) paradigms. Semiautomated analysis of all functional data was performed using Brain Voyager on an individual basis. Regions of interest for Brocas area, Wernickes area, and their contralateral homologues were drawn. The Euclidean coordinates of the center of gravidity (x, y, and z) of the respective blood oxygenation level-dependent (BOLD) activation cluster, and the correlation of the measured hemodynamic response to the applied reference function (r), relative BOLD signal change as BOLD signal characteristics were measured in each region of interest. Regional lateralization indexes were calculated for Brocas area, Wernickes area, and their contralateral homologues separately. Wilcoxons signed-rank test was applied for statistical comparisons (P values < .05 were considered significant). Ten of the 14 volunteers had three repeated measurements to test intrasession reproducibility and intersession reproducibility. RESULTS Overall activation rates for the four paradigms were 89% for covert SG, 82% for overt SG, 89% for covert WG, and 100% for overt WG. When comparing covert and overt paradigms, language localization was significantly different in 17% (Euclidean coordinates) and 19% (BOLD signal characteristics), respectively. Language lateralization was significantly different in 75%. Intrasubject and intersubject reproducibility was excellent, with 3.3% significant differences among all five parameters for language localization and 0% significant differences for language lateralization using covert paradigms. CONCLUSIONS Covert language paradigms (SG and WG) provided highly robust and reproducible localization and lateralization of essential language centers for scans performed on the same and different days. Their overt counterparts achieved confirmatory localization but lower lateralization capabilities. Reference data for presurgical application are provided.

Correlation of muscle BOLD MRI with transcutaneous oxygen pressure for assessing microcirculation in patients with systemic sclerosis.

To prospectively compare calf muscle BOLD MRI with transcutaneous oxygen pressure (TcPO2) measurement in patients with systemic sclerosis (SSc) and healthy volunteers and thereby get insight into the pathogenesis of vasculopathy in this connective tissue disorder.

Alterations of skeletal muscle microcirculation detected by blood oxygenation level-dependent MRI in a patient with granulomatosis with polyangiitis

SIR, Granulomatosis with polyangiitis (GPA) is a small vessel vasculitis that is associated with cardiovascular disease, which mainly determines the prognosis of GPA patients [1, 2]. Contradictory evidence has been published regarding accelerated atherosclerosis in GPA, which might cause cardiovascular morbidity [3, 4]. Blood oxygenation level-dependent (BOLD) MRI of skeletal muscle has become a valuable tool for the assessment of vascular pathologies such as atherosclerosis, diabetes mellitus and chronic compartment syndrome [5 7]. T2*-weighted MR signal of gradient-echo echo-planar imaging (EPI) sequences is sensitive to changes of oxyhaemoglobin concentration in small preand post-capillary vessels [8]. Here we present a case of a 73-year-old female GPA patient who was treated in our rheumatology clinic owing to severe myalgias. She had a 7-year history of GPA with nasopharyngeal symptoms, haemoptysis, arthritis, dysesthesias and renal involvement. During her actual admission, laboratory tests revealed leucopenia of 2.6/nl (reference range 3.5 10.0/nl), lymphopenia of 0.21/nl (0.9 3.3/nl), haematocrit 0.38 l/l (0.36 0.46 l/l), CRP 0.4 mg/l (<10 mg/l), BSG 10 mm/h (0 28 mm/h), ANCA 1 : 20 (<1 : 20), anti-MPO <2.5 U/ml (<5 U/ml) and anti-PR3 6 U/ml (<5 U/ml). Her blood pressure was 130/70 mmHg. She had no history of hypertension, diabetes mellitus or hyperlipidaemia. Her peripheral pulse status was normal and she never suffered from claudication. Recent maintenance immunosuppressive medication consisted of 150 mg azathioprine and 10 mg prednisone daily. MRI measurements were indicated owing to severe myalgias of both legs and performed on a 3.0-T scanner (Verio, Siemens Medical Solutions, Erlangen, Germany). Informed consent was obtained, and the study was approved by the local ethics committee (Ethikkommission beider Basel). A T2-weighted sequence revealed no signs of local inflammatory activity of the calves. For BOLD imaging, a healthy female volunteer controlled for age, BMI and physical activity served as control after providing consent. A multi-echo gradient-echo EPI sequence with fat suppression was used with a cuff compression paradigm as previously described [5, 9, 10]. Briefly, BOLD imaging was performed during the last minute of a 300 s resting period, 180 s of ischaemia and 400 s of reactive hyperaemia. Four axial slices (thickness 5 mm, gap 2.5 mm) were positioned in the upper calf. With each excitation, four echo images with increasing effective echo times were acquired. Inflow (initial signal intensity, I0) and oxygenation (susceptibility, T2*) effects were separated by a pixel-by-pixel least-square fit of a monoexponential decay to the signal intensities at the four different echo times (TE1 4 of 9.3, 20.1, 31.0 and 41.5 ms) according to S(I0, T2*) = I0 exp( TE1 4/T2*). T2* maps were computed, supplemented with T1-reference images and ROIs placed in the soleus, gastrocnemius and peroneus, excluding pixels of bones and vessels (Fig. 1).

Correlation of skeletal muscle blood oxygenation level‐dependent MRI and skin laser doppler flowmetry in patients with systemic sclerosis

To investigate the origin of skeletal muscle BOLD MRI alterations in patients with systemic sclerosis (SSc) by correlating BOLD MRI T2* signal of calf muscles with microcirculatory blood flow of calf skin measured by laser Doppler flowmetry (LDF).

Assessment of Skeletal Muscle Microperfusion Using MRI

Blood oxygenation level-dependent (BOLD) MRI, arterial spin labeling (ASL) and dynamic contrast enhancement (DCE) are current magnetic resonance imaging (MRI) techniques allowing the non-invasive functional assessment of peripheral microvasculature in healthy and diseased individuals. The functional imaging of skeletal muscle microvasculature helps to understand muscular and vascular physiology and alterations of microcirculation under certain pathological conditions such as peripheral arterial occlusive disease, diabetes mellitus, chronic compartment syndrome and rheumatic disorders. BOLD MRI uses blood as an endogenous contrast agent provided by the different magnetic properties of oxy- and deoxyhemoglobin. The BOLD contrast in skeletal muscle tissue primarily arises from the microcirculation yielding a very sensitive tool for alterations of the physiological oxygen supply and demand. However, the complex nature of the BOLD contrast’s origin also entails a variety of variables complicating the interpretation of BOLD signal changes. ASL’s ability to directly measure muscle perfusion may prove to be a powerful tool for the evaluation of disease progression and the evaluation of therapies aimed at improving muscle perfusion. As is the case with BOLD MRI, this holds particularly true for patients who are unable to receive contrast agents, a collective which is often afflicted with vascular impairments. Dynamic contrast enhanced MRI may contribute considerably to objectively evaluate many musculoskeletal diseases through its ability to measure multiple microvascular properties. The potential of these three MRI methods to non-invasively assess disease severity and the efficacy of new therapeutic strategies, such as stem cell and gene therapy, renders them as very appealing future research targets.

Gadofosveset--a blood pool contrast agent used with MRI to detect obscure gastrointestinal bleeding: a case report.

Gadofosveset—A Blood Pool Contrast Agent Used with MRI to Detect Obscure Gastrointestinal Bleeding: A Case Report