Assessment of cutaneous microcirculation in unaffected skin regions by transcutaneous oxygen saturation monitoring and Laser Doppler flowmetry in systemic sclerosis.

We assessed the cutaneous microcirculatory reactivity of a clinically unaffected skin region in patients with systemic sclerosis (SSc) compared to healthy controls by measuring transcutaneous oxygen saturation (TcPO2) and Laser Doppler flowmetry (LDF).Twelve consecutive patients with SSc and twelve healthy controls were subjected to TcPO2 monitoring and LDF during cuff-induced ischemia and reactive hyperemia in order to measure the skin oxygen tension and the microcirculatory blood flow. Mean minimal and maximal values of oxygen tension and blood flow, time to peak (TTP), and declining slopes after peaking (slope) were compared between patients with SSc and controls.Compared to the controls, TcPO2 values in SSc were similar during ischemia and diminished during reactive hyperemia, with longer TTP, and a slower return to baseline (-60% vs. -58% , p = 1.000, +76% vs. +210% , p = 0.047, 137 s vs. 108 s, p = 0.028, -0.009% /s vs. -0.019% /s, p = 0.021, respectively). LDF values, however, did not differ significantly between patients with SSc and controls.Unaffected skin regions of SSc patients showed a significantly diminished postischemic vasodilatory reactivity when assessed by TcPO2 monitoring, but not by LDF, indicating that vasculopathy may represent an early mechanism in the onset of skin sclerosis. TcPO2 measurement may help to detect changes in the microcirculation in SSc with no skin affection.

Assessing the end-organ in peripheral arterial occlusive disease-from contrast-enhanced ultrasound to blood-oxygen-level-dependent MR imaging.

Peripheral arterial occlusive disease (PAOD) is a result of atherosclerotic disease which is currently the leading cause of morbidity and mortality in the western world. Patients with PAOD may present with intermittent claudication or symptoms related to critical limb ischemia. PAOD is associated with increased mortality rates. Stenoses and occlusions are usually detected by macrovascular imaging, including ultrasound and cross-sectional methods. From a pathophysiological view these stenoses and occlusions are affecting the microperfusion in the functional end-organs, such as the skin and skeletal muscle. In the clinical arena new imaging technologies enable the evaluation of the microvasculature. Two technologies currently under investigation for this purpose on the end-organ level in PAOD patients are contrast-enhanced ultrasound (CEUS) and blood-oxygen-level-dependent (BOLD) MR imaging (MRI). The following article is providing an overview about these evolving techniques with a specific focus on skeletal muscle microvasculature imaging in PAOD patients.

Correlation of skeletal muscle blood oxygenation level-dependent MRI and skin laser Doppler flowmetry in patients with systemic sclerosis.

PURPOSE: 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). MATERIALS AND METHODS: BOLD MRI (3T) and LDF measurements were performed in 12 consecutive SSc patients (6 women, 6 men; mean age 54.0 ± 10.0 years) and 12 healthy volunteers (4 men, 8 women; mean age 44.7 ± 13.1 years). For both modalities, the same cuff compression paradigm at mid-thigh level was used. LDF datasets were acquired using a PeriScan PIM II Imager (Perimed AB, Stockholm, Sweden) at the upper calf corresponding to the level of MR imaging. Cross-correlations of BOLD and LDF signal intensity changes depending on time lags between both time series were calculated. RESULTS: Maximal cross-correlations of BOLD T2* and LDF measurements were calculated as 0.93 (healthy volunteers) and 0.94 (SSc patients) for a BOLD time lag of approximately 10 s. Key parameter analysis suggested that in contrast to hyperemic BOLD signal loss at maximum value in SSc patients, ischemic T2* decrease cannot be explained by differences of tissue perfusion. CONCLUSION: Skeletal muscle BOLD T2* signal in SSc patients is closely correlated with changes of microperfusion as detected by LDF.

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

PURPOSE: 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. MATERIALS AND METHODS: Twelve patients with SSc (6 women and 6 men, mean age 53.5 ± 10.0 years) and 12 healthy volunteers (4 men and 8 women, mean age 47 ± 12.1 years) were examined using muscle BOLD MRI and TcPO2. A cuff compression at mid-thigh level was performed to provoke ischemia and reactive hyperemia. BOLD measurements were acquired on a 3 Tesla whole body-scanner in the upper calf region using a multi-echo EPI-sequence with four echo-times (TE: 9/20/31/42 ms) and a repetition time of 2 s. Empirical cross-correlation analysis depending on time lags between BOLD- and TcPO2-measurements was performed. RESULTS: Maximal cross-correlation of BOLD T2*- and TcPO2-measurements was calculated as 0.93 (healthy volunteers) and 0.90 (SSc patients) for a time lag of approximately 40 s. Both modalities showed substantial differences regarding time course parameters between the SSc patients and healthy volunteers. CONCLUSION: Skeletal muscle BOLD MRI correlated very well with TcPO2 . T2* changes seem to reflect reoxygenation deficits in deeper muscle tissue of SSc patients.

ECG-triggered non-enhanced MR angiography of peripheral arteries in comparison to DSA in patients with peripheral artery occlusive disease.

OBJECT: The purpose of this study was to evaluate peripheral non-enhanced-MRA (NE-MRA) acquired with a 3D Turbo Spin Echo sequence with electrocardiographt (ECG) triggering in comparison to Digital Subtraction Angiography (DSA) as the gold standard in symptomatic peripheral artery occlusive disease (PAOD) patients. MATERIALS AND METHODS: This IRB approved prospective study included 23 PAOD patients from whom three patients had to be excluded. The remaining 20 subjects were included in the analysis (15 male; mean age 62.4 ± 15.3 years). The patients first underwent DSA followed by NE-MRA on a 1.5-T whole body scanner within 24 h after the DSA study. A NATIVE (Non-contrast Angiography of the Arteries and Veins) SPACE (Sampling Perfection with Application Optimized Contrast by using different flip angle Evolution) sequence at four levels (pelvis, upper leg, knee region and lower leg) was acquired. For evaluation purposes, subtracted standardized MIP (maximum intensity projection) images were generated from the NE-MRA data sets. Qualitative assessment of NE-MRA images in reference to the corresponding DSA images, as well as blinded stenosis grading of preselected segments in NE-MRA images were performed by two experienced readers. Image quality in 95 corresponding arterial segments was rated from 1 (good) to 4 (inadequate) directly comparing the NE-MRA with the corresponding DSA segment as the gold standard. Blinded stenosis grading consisted of 66 preselected stenoses rated from 1 (<10 %) to 4 (>90 %) in NE-MRA which were compared to the grade in the corresponding DSA. RESULTS: The mean image quality of NE-MRA in comparison to DSA was 2.7 ± 1.1 (reader 1) and 3.0 ± 1.0 (reader 2). The kappa value indicating interobserver agreement was 0.34; readers 1 and 2 rated the image quality as good in 21 % and 3 %, sufficient in 19 % and 41 %, limited in 29 % and 14 % and inadequate in 31 % and 42 %, respectively. Stenosis graduation revealed significantly higher grades in NE-MRA (reader 1: 3.0 ± 0.7, p < 0.001 and reader 2: 3.1 + 0.8, p < 0.001) compared to DSA (mean value DSA 2.7 ± 0.8). The kappa value indicating interobserver agreement concerning stenosis grading was 0.59. CONCLUSION: NE-MRA revealed a relatively high number of inadequate quality segments. This is in line with recently published comparable studies of the similar SPACE NE-MRA techniques. Further advance of NE-MRA techniques remains desirable for patients with PAOD.

Impaired skeletal muscle microcirculation in systemic sclerosis.

INTRODUCTION: Muscle symptoms in systemic sclerosis (SSc) may originate from altered skeletal muscle microcirculation, which can be investigated by means of blood oxygenation level dependent (BOLD) magnetic resonance imaging (MRI). METHODS: After ethics committee approval and written consent, 11 consecutive SSc patients (5 men, mean age 52.6 years, mean SSc disease duration 5.4 years) and 12 healthy volunteers (4 men, mean age 45.1 years) were included. Subjects with peripheral arterial occlusive disease were excluded. BOLD MRI was performed on calf muscles during cuff-induced ischemia and reactive hyperemia, using a 3-T whole-body scanner (Verio, Siemens, Erlangen, Germany) and fat-suppressed single-short multi-echo echo planar imaging (EPI) with four different effective echo times. Muscle BOLD signal time courses were obtained for gastrocnemius and soleus muscles: minimal hemoglobin oxygen saturation (T2*min) and maximal T2* values (T2*max), time to T2* peak (TTP), and slopes of oxygen normalization after T2* peaking. RESULTS: The vast majority of SSc patients lacked skeletal muscle atrophy, weakness or serum creatine kinase elevation. Nevertheless, more intense oxygen desaturation during ischemia was observed in calf muscles of SSc patients (mean T2*min -15.0%), compared with controls (-9.1%, P = 0.02). SSc patients also had impaired oxygenation during hyperemia (median T2*max 9.2% vs. 20.1%, respectively, P = 0.007). The slope of muscle oxygen normalization was significantly less steep and prolonged (TTP) in SSc patients (P<0.001 for both). Similar differences were found at a separate analysis of gastrocnemius and soleus muscles, with most pronounced impairment in the gastrocnemius. CONCLUSIONS: BOLD MRI demonstrates a significant impairment of skeletal muscle microcirculation in SSc.

Skeletal muscle BOLD MRI: from underlying physiological concepts to its usefulness in clinical conditions.

Blood oxygenation-level dependent (BOLD) MRI has gained particular attention in functional brain imaging studies, where it can be used to localize areas of brain activation with high temporal resolution. To a higher degree than in the brain, skeletal muscles show extensive but transient alterations of blood flow between resting and activation state. Thus, there has been interest in the application of the BOLD effect in studying the physiology of skeletal muscles (healthy and diseased) and its possible application to clinical practice. This review outlines the potential of skeletal muscle BOLD MRI as a diagnostic tool for the evaluation of physiological and pathological alterations in the peripheral limb perfusion, such as in peripheral arterial occlusive disease. Moreover, current knowledge is summarized regarding the complex mechanisms eliciting BOLD effect in skeletal muscle. We describe technical fundaments of the procedure that should be taken into account when performing skeletal muscle BOLD MRI, including the most often applied paradigms to provoke BOLD signal changes and key parameters of the resulting time courses. Possible confounding effects in muscle BOLD imaging studies, like age, muscle fiber type, training state, and drug effects are also reviewed in detail.

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.

PURPOSE: 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. MATERIALS AND METHODS: Two consecutive skeletal muscle BOLD magnetic resonance imaging (MRI) measurements in eight healthy volunteers were performed on 1.5 T and 3.0 T whole-body MRI scanners. For both measurements a fat-saturated multi-shot multiecho gradient-echo EPI sequence was applied. Temporary vascular occlusion was induced by suprasystolic cuff compression of the thigh. T2 time courses were obtained from two different calf muscles and characterized by typical curve parameters. Ischemia- and hyperemia-induced changes in R2 (ΔR2) were calculated for both muscles in each volunteer at the two field strengths. RESULTS: Skeletal muscle BOLD changes are dependent on magnetic field strength as the ratio ΔR2(3.0 T)/ΔR2(1.5 T) was found to range between 1.6 and 2.2. Regarding time course characteristics, significantly higher relative T2 changes were found in both muscles at 3.0 T. CONCLUSION: The present study shows an approximately linear field strength dependence of ΔR2 in the skeletal muscle in response to ischemia and reactive hyperemia. Using higher magnetic fields is advisable for future BOLD imaging studies of peripheral limb pathologies.

Effects of percutaneous transluminal angioplasty on muscle BOLD-MRI in patients with peripheral arterial occlusive disease: preliminary results.

The purpose was to evaluate the effect of percutaneous transluminal angioplasty (PTA) of the superficial femoral artery (SFA) on the blood oxygenation level-dependent (BOLD) signal change in the calf musculature of patients with intermittent claudication. Ten patients (mean age, 63.4+/-11.6 years) with symptomatic peripheral arterial occlusive disease (PAOD) caused by SFA stenoses were investigated before and after PTA. Patients underwent BOLD-MRI 1 day before and 6 weeks after PTA. A T2*-weighted single-shot multi-echo echo-planar MR-imaging technique was applied. The BOLD measurements were acquired at mid-calf level during reactive hyperaemia at 1.5 T. This transient hyperperfusion of the muscle tissue was provoked by suprasystolic cuff compression. Key parameters describing the BOLD signal curve included maximum T2* (T2*(max)), time-to-peak to reach T2*(max) (TTP) and T2* end value (EV) after 600 s of hyperemia. Paired t-tests were applied for statistic comparison. Between baseline and post-PTA, T2*(max) increased from 11.1+/-3.6% to 12.3+/-3.8% (p=0.51), TTP decreased from 48.5+/-20.8 s to 35.3+/-11.6 s (p=0.11) and EV decreased from 6.1+/-6.4% to 5.0+/-4.2% (p=0.69). In conclusion, BOLD-MRI reveals changes of the key parameters T2*(max), TTP, and EV after successful PTA of the calf muscles during reactive hyperaemia.

Calf muscles at blood oxygen level-dependent MR imaging: aging effects at postocclusive reactive hyperemia.

PURPOSE: To prospectively investigate age-related changes in muscle reperfusion by using blood oxygen level-dependent (BOLD) magnetic resonance (MR) imaging of the calf in young and elderly healthy volunteers during postocclusive reactive hyperemia. MATERIALS AND METHODS: Institutional review board approval and informed consent were obtained. Eleven healthy elderly (mean age, 64.0 years +/- 6.4 [standard deviation]; six men, five women) and 17 healthy young volunteers (mean age, 30.3 years +/- 6.5; seven men, 10 women) underwent muscle BOLD MR imaging of the calf. A fat-suppressed T2*-weighted single-shot multiecho echo-planar imaging sequence was used. Temporary vascular occlusion was induced with suprasystolic cuff compression of the thigh. T2* time courses of the muscle BOLD MR signal intensity were obtained from four calf muscles and were characterized by the following curve parameters: hyperemia peak value, time to peak, and T2* end value after 360 seconds of hyperemia. Differences in these parameters between the two cohorts were assessed by using a Student t test. RESULTS: Considerably lower T2* maxima were observed in the elderly group during hyperemia (P < .005), with a mean hyperemia peak value of 13.1% +/- 3.0 compared with 18.9% +/- 4.8 in young healthy adults. Peaking occurred earlier in the elderly group (P < .05), with a mean time to peak of 32.2 seconds +/- 10.6 compared with 43.1 seconds +/- 10.7 in young adults. Furthermore, the elderly group had a significantly slower decrease of the muscle BOLD signal after the hyperemia peak (P < .001), which led to a higher end value of 8.6% +/- 3.0 compared with 2.6% +/- 2.1 in the young group. CONCLUSION: BOLD MR imaging results of the calf demonstrated statistically significant age-dependent differences in the rate, intensity, and recovery of the postocclusive muscle BOLD signal.

Intraarterial contrast-enhanced MR aortography with and without parallel acquisition technique in patients with peripheral arterial occlusive disease.

OBJECTIVE: Repeated intraarterial gadolinium injections are necessary in endovascular MRI-guided interventions; therefore a low-dose protocol with a short acquisition time is preferable. The purpose of this study was to conduct a quantitative comparison of intraarterial MR aortograms obtained with and without high-speed parallel acquisition technique. SUBJECTS AND METHODS: Intraarterial MR aortography was performed at 1.5 T on nine patients with peripheral arterial occlusive disease and in an aortic phantom with pulsatile flow. A 3D fast low-angle shot MRI sequence was used for standard technique (acquisition time, 20 seconds) and for parallel acquisition technique (acquisition time, 14 seconds). In all patients, a pigtail catheter was left in the suprarenal position after digital subtraction angiography. Contrast-enhanced intraarterial MR aortography was performed after automated injection of 50 mmol/L gadoterate dimeglumine at an injection rate of 4 mL/s. Contrast-to-noise ratio (CNR) and image quality were evaluated in both imaging series at different locations. In an aortic phantom with pulsatile flow, CNR was determined 1, 30, and 60 cm distal to the catheter tip with standard and parallel acquisition techniques. RESULTS: In all patients, intraarterial MR aortography was feasible with both acquisition techniques. No significant difference in CNR or image quality was observed in the patient study. Similar results were calculated for the pulsatile aortic flow phantom at all locations. CONCLUSION: Intraarterial MR aortography is feasible with parallel acquisition technique without a significant loss of CNR. This technique reduces contrast agent consumption approximately 30% owing to an approximately 30% reduction in acquisition time.

Calf muscles imaged at BOLD MR: correlation with TcPO2 and flowmetry measurements during ischemia and reactive hyperemia--initial experience.

PURPOSE: To prospectively compare the blood oxygen level-dependent (BOLD) magnetic resonance (MR) signal intensity of calf muscle during ischemia and reactive hyperemia with laser Doppler flowmetry (LDF) and transcutaneous oxygen pressure (TcPo2) measurements, two parameters routinely used to evaluate peripheral arterial occlusive disease. MATERIALS AND METHODS: The study was institutional review board approved; all volunteers gave informed consent. Fifteen healthy volunteers (eight male, seven female; mean age, 33.0 years +/- 6.1 [standard deviation]) underwent LDF, TcPo2 measurement, and BOLD MR imaging of the calf during ischemia and reactive hyperemia. The BOLD signal intensity of the gastrocnemius muscle was measured at 1.5-T single-shot multiecho gradient-echo echo-planar imaging. Time to half ischemia minimum (THIM), time to half hyperemia peak (THHP), and time to peak (TTP) after cuff deflation were measured with each method. Correlation coefficients (CCs) for associations of BOLD response with LDF and TcPo2 time courses were calculated. Student t testing of key BOLD MR, LDF, and TcPo2 measurement parameters was performed. RESULTS: During ischemia, normalized LDF and TcPo2 measurements decreased similarly to BOLD MR signal intensity (CCs: 0.86 and 0.96 for associations with LDF and TcPo2 measurements, respectively). Mean THIM values were 136.0, 82.5, and 121.3 seconds for BOLD MR, LDF (P < .01), and TcPo2 (P > .05) measurements, respectively. During early reactive hyperemia, LDF and TcPo2 measurements increased rapidly to peak values, similarly to BOLD MR signal intensity (CCs: 0.81 and 0.78, respectively). Mean THHP values were 26.0, 12.5, and 44.0 seconds for BOLD MR, LDF (P < .01), and TcPo2 (P < .01) measurements, respectively. Mean TTP values were 48.7, 47.5, and 98.0 seconds for BOLD MR, LDF (P > .05), and TcPo2 (P < .01) measurements, respectively. CONCLUSION: BOLD MR imaging of calf muscles-depending on underlying key parameters-has moderate to good correlation with LDF and TcPo2 measurements during ischemia and reactive hyperemia.

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 (deltaT2*(max)) and time to peak to reach deltaT2*(max) for gastrocnemius, soleus, tibial anterior, and peroneal muscle were evaluated. Compared with the non-PAOD group, patients revealed significantly lower deltaT2*(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 (deltaT2*(max); time to peak) in PAOD patients compared with age-matched non-PAOD controls.

Intraarterial MR angiography and DSA in patients with peripheral arterial occlusive disease: prospective comparison.

PURPOSE: To prospectively evaluate the accuracy of intraarterial magnetic resonance (MR) angiography in the depiction of significant stenoses and occlusions, with intraarterial digital subtraction angiography (DSA) serving as the reference standard. MATERIALS AND METHODS: Approval of the local ethics committee and informed consent were obtained. Twenty patients (11 men; nine women; age range, 48-86 years; mean age, 69.5 years+/-11.2 [standard deviation]) with symptomatic peripheral arterial occlusive disease (PAOD) were prospectively enrolled. After percutaneous transluminal angioplasty (PTA), intraarterial MR angiography was performed in the thigh and the calf with a 1.5-T MR imager in two consecutive runs. Intraarterial MR angiography was performed with a low-dose injection protocol (ie, two 20-mL injections of a 50-mmol gadolinium-based contrast agent). Moderate stenoses (luminal narrowing50%) or vessel occlusions; 95% confidence intervals (CIs) were calculated for sensitivity and specificity. RESULTS: Intraarterial DSA revealed 78 moderate stenoses, 57 significant stenoses, and 28 occlusions. Sensitivity, specificity, and accuracy of intraarterial MR angiography in the characterization of significant stenoses or occlusions were 92% (95% CI: 72%, 99%), 94% (95% CI: 82%, 98%), and 93%, respectively, in femoropopliteal arteries and 93% (95% CI: 83%, 98%), 71% (95% CI: 51%, 86%), and 86%, respectively, in infrapopliteal arteries. The main artifact observed with intraarterial MR angiography was venous contamination (12%). CONCLUSION: Intraarterial MR angiography is an accurate method used to depict significant stenoses and occlusions in lower extremity arteries with a low-dose injection protocol.

Intraarterial versus IV gadolinium injections for MR angiography: quantitative and qualitative assessment of the infrainguinal arteries.

OBJECTIVE: Our purpose was to quantitatively and qualitatively compare 3D intraarterial (IA) gadolinium-enhanced MR angiography (IA MRA) versus the standard of reference of MR angiography, 3D IV gadolinium-enhanced MR angiography (IV MRA), in patients with peripheral arterial occlusive disease (PAOD) for use during catheter-based MR-guided endovascular interventions. CONCLUSION: IA MRA provides image quality of the infrainguinal arteries in PAOD patients comparable to IV MRA with a significantly improved assessment of the infrapopliteal arteries due to reduced venous contamination. Further benefits of IA MRA include usage of only very low doses of gadolinium and simplified bolus timing.

Lower extremity: low-dose contrast agent intraarterial MR angiography in patients--initial results.

Institutional review board approval and patient consent were obtained. A low-dose injection protocol for intraarterial three-dimensional (3D) gadolinium-enhanced magnetic resonance (MR) angiography was derived from femoral flow phantom studies and prospectively evaluated in patients with peripheral arterial occlusive disease (PAOD). All MR angiograms were obtained at 1.5 T with a T1-weighted gradient-echo sequence. MR angiograms of a gadolinium dilution series (0.8-200.0 mmol/L) were acquired in a femoral phantom at different flow rates. Signal-to-noise ratios (SNRs) above the 75% threshold of the measured maximum were considered optimal. The lowest optimal concentration was injected intraarterially in nine patients to obtain 3D MR angiograms of the thigh and calf station. Contrast-to-noise ratios (CNRs) were calculated for four arterial segments. The low optimal concentration of 50 mmol/L (20-mL bolus volume), about 5% of the total permissible dose, showed SNRs larger than the 75% threshold in the phantom study. In patients, this concentration led to high-spatial-resolution angiograms with mean CNRs of 70.0 +/- 14.5 (+/- standard deviation) for the superficial femoral artery and 47.5 +/- 13.4 at the infrapopliteal level. Low-dose contrast agent intraarterial 3D MR angiography showed high arterial enhancement, enabling assessment of lower extremity arteries in patients with PAOD and multiple injections--a crucial precondition for MR-guided endovascular interventions.

Infragenual cuff-compression reduces venous contamination in contrast-enhanced MR angiography of the calf.

PURPOSE: To reduce venous contamination at the calf level in three-dimensional contrast-enhanced MR angiography (CE-MRA) by applying continuous infragenual cuff-compression. MATERIALS AND METHODS: Ten patients with clinically relevant peripheral arterial occlusive disease (PAOD) underwent dynamic three-dimensional CE-MRA of the calf. Six consecutive measurements were acquired with the first measurement serving as mask. Cuff-compression of 50 mmHg was attached below the knee. To allow intra-individual comparison, compression was applied unilaterally. The cuff was inflated three minutes before scanning and was continued throughout the MRA session. Venous contamination and arterial visualization scores were ranked using a five-point rating scale. Contrast-to-noise ratios (CNRs) of superficial enhancing calf-veins on the uncompressed and compressed calf sides were evaluated. An asymmetry index (AI) defined by CNR(mean) (uncompressed)/CNR(mean) (compressed) was introduced to describe the ratio in venous contrast agent supply between both sides quantitatively. RESULTS: Three-dimensional CE-MRA of the calves demonstrated significantly lower superficial venous contamination scores (P < 0.004) and clearly improved arterial visualization (P < 0.009) on the compressed side. Additionally, AI values were larger than 1 (P < 0.02), indicating a higher contrast agent supply in the superficial veins on the uncompressed side. CONCLUSION: Infragenual cuff-compression minimizes venous overlay in three-dimensional CE-MRA at calf level by reduction of contrast agent supply in the superficial veins.

Dose optimization for dynamic time-resolved contrast-enhanced 3D MR angiography of pulmonary circulation.

OBJECTIVE: The aim of this study was to optimize contrast media dose for assessment of pulmonary circulation with dynamic time-resolved contrast-enhanced 3D MR angiography. SUBJECTS AND METHODS. Twenty healthy volunteers (20-38 years old; mean [+/- SD], 27.2 +/- 4.5 years) were examined prospectively using turbo fast low-angle shot MR angiography (TR/TE, 2.4/1.04). Ten consecutive coronal 3D slabs with a frame rate of 3.2-sec duration were acquired during injection of contrast media at a rate of 4 mL/sec. Signal intensities were measured in various vessels and pulmonary parenchyma. Maximum signal-intensity enhancement (DeltaSI(max)) and time to peak enhancement were calculated. Depiction of pulmonary vessels and pulmonary parenchyma was scored according to an image quality score. RESULTS: Central pulmonary arteries were well visualized at all tested doses. Segmental arteries, however, were blurry with 0.025 or 0.05 mmol/kg; image quality was improved at 0.1 mmol/kg of gadoterate meglumine (p < 0.05). Image quality did not further improve at 0.2 mmol/kg (p = not significant). Values for DeltaSI(max) in the pulmonary trunk were 38.9 +/- 9.7, 64.1 +/- 9.1, 79.7 +/- 12.2, and 96 +/- 6.0 at 0.025, 0.5, 0.1, and 0.2 mmol/kg of gadoterate meglumine, respectively. Pulmonary parenchyma showed almost no enhancement at 0.025 and 0.5 mmol/kg of gadoterate meglumine (DeltaSI(max) = 1.6 +/- 1.1 and 1.6 +/- 1.2, respectively), but better visualization was shown with 0.1 and 0.2 mmol/kg of gadoterate meglumine (DeltaSI(max) = 2.9 +/- 0.8 and 6.7 +/- 2.1, respectively). Time from peak enhancement in pulmonary arteries to peak enhancement in veins was independent of dose. CONCLUSION: A dose of 0.1 mmol/kg of gadolinium chelate allows depiction of pulmonary arteries and qualitative assessment of pulmonary parenchyma. Thus, 0.1 mmol/kg can be recommended for dynamic contrast-enhanced 3D MR angiography.