Magnetresonanztomographische Diagnostik der peripheren Durchblutung*

Ziel:

Eignung und kasuistische Anwendung der dynamischen kontrastverstärkten Magnetresonanztomographie (DCEMRT) zur Erfassung der peripheren Durchblutung im Unterschenkel.

Patienten und Methodik:

Bei einer Patientin mit peripherer arterieller Verschlusskrankheit (pAVK), einem Patienten mit koronarer Herzkrankheit (KHK) ohne klinische Zeichen einer pAVK, einer Normalperson mit ausreichender körperlicher Aktivität gemäß Freiburger Aktivitätsscore und zwei Leistungssportlern wird der krurale Muskelstatus mit einer isometrischen Maximalkraftmessung bestimmt. Nach Kalibrierung des speziell konstruierten Plantarflexionsergometers MRPEDALO^® zur Durchführung auxotoner Muskelarbeit durch 1-minütige alternierende Fußextension und -flexion im MRTGerät wird die DCE-MRT vor und nach Belastung durchgeführt (T1w 2D-FLASH-GE-Sequenz mit TR/TE/α: 100 ms/6 ms/70°; Bildfeld: 400; Matrix: 81 × 256; Schichtdicke: 10 mm; Akquisitionen: 73 à 8,3 s; Messzeit: 9,24 min; Bolusapplikation von Magnevist^®, Schering, 0,02 ml/kg KG, 20 ml NaCl Bolus, Flow 2 ml/s, kubitale 22G-Kanüle). Semiquantitative Kurvenauswertung mit DynaVision^® (MeVis gGmbH).

Ergebnisse:

Die Messung der peripheren Durchblutung benötigt geeignete Belastungstests. Nach Muskelarbeit zwischen 52 Wattsekunden (Ws) und 244 Ws bzw. 0,65 W und 4,07 W, die in Relation zur trainingsbedingt stark unterschiedlichen isometrischen Maximalkraft für eine interindividuell annähernd vergleichbare Belastung sprechen, finden sich ausgeprägte Änderungen der Signalintensitäts-(SI-)Kurven für den Musculus peronaeus, in geringerem Ausmaß auch für den Musculus tibialis anterior, die mit der Time-to-Peak (TTP) und der Mean-Intensityto- Time-Ratio (MITR) sowie dem individuellen Muskelstatus korrelieren. Der Musculus gastrocnemius zeigt dagegen vergleichsweise geringe Kurvenänderungen. Die relative Verkürzung der TTP und Verlängerung der MITR nach Belastung, der eine verbesserte Mobilisierung der Durchblutungsreserve entspricht, ist bei Leistungssportlern besonders deutlich ausgeprägt. Die DCEMRT spricht darüber hinaus für individuell unterschiedliche Muskelkoordinationsstrategien trotz in der Größenordnung vergleichbarer Flexions- und Extensionsbelastung.

Schlussfolgerung:

Die nichtinvasive semiquantitative Messung der belastungsabhängigen Muskeldurchblutung der Unterschenkel ist mit der DCE-MRT möglich, bedarf aber für inter- und intraindividuelle Vergleiche einer weiteren Standardisierung. Die Methode besitzt diagnostisches Potential für das Therapiemonitoring sowie die Sport- und Rehabilitationsmedizin durch Visualisierung und Quantifizierung der peripheren Mikrozirkulation und additiver Information über die muskuläre Koordination.

Purpose:

This article describes the potential of dynamic contrast- enhanced magnetic resonance tomography (DCE-MRT) for the visualization and quantification of blood flow of lower leg muscles at rest and after individually adjusted muscular exercise.

Patients and Methods:

Five cases were chosen to exemplify the qualitative and semi-quantitative blood flow evaluation in the lower leg muscles. The crural muscle state was determined with an isometric maximal strength measurement from a female patient with peripheral arterial occlusive disease (pAVK), a male patient with coronary heart disease (KHK) without clinical signs of a pAVK, a volunteer with sufficient physical activity in accordance with the Freiburg Questionnaire of Physical Activity and two professional athletes. After calibration of the plantarflexion ergometer MR-PEDALO^® (Figures 2a and 2b) for the execution of auxotonic muscle work a 1- minute alternating foot extension and flexion exercise on MRPEDALO^® was performed in the MR machine. Instead of the lower leg splint shown in Figures 2a and 2b the MR coil fits exactly in MR-PEDALO^® used for DCE-MRT. Mechanical work performed during the 1-minute exercise ranged from 52 watt seconds (Ws) to 244 Ws (0.65 W to 4.07 W), indicating similar interindividual work loads in relation to the individual maximum isometric strength. DCE-MRT was performed at rest and immediately after auxotonic exercise test (T1w 2DFLASH- GE sequence with TR/TE/α: 100 ms/6 ms/70°; field of view: 400; matrix: 81 × 256; slice thickness: 10 mm; acquisitions: 73 at 8.3 s each; total examination time: 9.24 min; bolus application of Magnevist^®, Schering, 0.02 ml/kg kg, 20 ml bolus NaCl, flow 2 ml/s, 22G cannula in a cubital vein). Signal intensity (SI) curves were analyzed with DynaVision^® (MeVis gGmbH, Bremen, Germany).

Results:

Measuring peripheral blood flow needs appropriate muscular stress tests. The SI-curves of the region of interest (ROI) representing the peroneus, tibialis anterior and gastrocnemius muscle run almost parallel at rest. Workloads between 52 Ws and 244 Ws (0.65 W and 4.07 W), similar in relation to the individual maximum isometric strength, induce distinctive changes of the upslope, wash-in, peak and washout of SI-curves preferably for the peroneus muscle and less predominant also for the tibialis anterior muscle and gastrocnemius muscle respectively. The first case, a 55-year-old female patient with peripheral arterial occlusive disease (pAVK) stage Fontaine IIb before (Figure 3a) and after (Figure 3b) percutaneous transluminal angioplasty (PTA) of a right femoral artery stenosis shows after interventional treatment a rapid post-exercise SI-increase in the peroneus muscle. The steeper SI-curve indicates a better contrast medium inflow due to an improved perfusion. The second case, a 65-year-old man suffering from coronary heart disease without clinical signs of pAVK (Figure 4) exercised with a workload of 92 Ws. After stress test the ROI for the peroneus muscle shows a clear intensity increase. After exercise the SI-curve for the tibialis anterior muscle shows a similar, but less predominant change while the shape of the SI-curve of the gastrocnemius muscle remains mainly identical. A 23-year-old male person with average physical activity (Figure 5) performed DCE-MRT of the left lower leg after stress test with 172 Ws demonstrating a rapid signal increase in the peroneus muscle while the synergistic tibialis anterior muscle and antagonistic gastrocnemius muscle show a comparatively slow contrast-medium wash-in. A 26-year-old male athlete (Figure 6) exercised with 196 Ws showing a rapid contrast medium inflow in the peroneus muscle and initially also in the synergistic tibialis anterior muscle. A contrast-medium wash-out appears in both muscles, while the shape of the gastrocnemius muscle SI-curve remains substantially unchanged. A 26-year-old female athlete (Figure 7) exercised with 244 Ws. Post exercise SI-curves show a distinctive and rapid increase of contrast medium wash-in with a sharp peak particularly in the peroneus muscle and similarly in the tibialis anterior and gastrocnemius muscle. After exercise all SI-curves show a wash-out phase.

Conclusion:

SI-curves show relative increase in correlation with Time-to-Peak (TTP) decrease and Mean-Intensity to Time Ratio (MITR) increase indicating blood flow reserve mobilization after exercise. Individual muscle state seems to be linked to muscle recruitment and muscle coordination reflected by post-exercise SI-curves. The gastrocnemius muscle shows comparatively low SI-curve changes after muscular load test. Further methodological standardization and optimization of the stress test is mandatory to assure intra- and interindividual comparisons. Due to direct visualization and quantitative evaluation of the peripheral microcirculation DCE-MRT has a diagnostic potential for monitoring therapeutic response in peripheral circulation disorders and sports medicine.