title: Real-time magnetic resonance imaging of deep venous flow during muscular exercise-preliminary experience.
abstract: BACKGROUND
  The accurate assessment of peripheral venous flow is important for the early diagnosis and treatment of disorders such as deep-vein thrombosis (DVT) which is a major cause of post-thrombotic syndrome or even death due to pulmonary embolism. The aim of this work is to quantitatively determine blood flow in deep veins during rest and muscular exercise using a novel real-time magnetic resonance imaging (MRI) method for velocity-encoded phase-contrast (PC) MRI at high spatiotemporal resolution.
  
  
  METHODS
  Real-time PC MRI of eight healthy volunteers and one patient was performed at 3 Tesla (Prisma fit, Siemens, Erlangen, Germany) using a flexible 16-channel receive coil (Variety, NORAS, Hoechberg, Germany). Acquisitions were based on a highly undersampled radial FLASH sequence with image reconstruction by regularized nonlinear inversion at 0.5×0.5×6 mm3spatial resolution and 100 ms temporal resolution. Flow was assessed in two cross-sections of the lower leg at the level of the calf muscle and knee using a protocol of 10 s rest, 20 s flexion and extension of the foot, and 10 s rest. Quantitative analyses included through-plane flow in the right posterior tibial, right peroneal and popliteal vein (PC maps) as well as signal intensity changes due to flow and muscle movements (corresponding magnitude images).
  
  
  RESULTS
  Real-time PC MRI successfully monitored the dynamics of venous flow at high spatiotemporal resolution and clearly demonstrated increased flow in deep veins in response to flexion and extension of the foot. In normal subjects, the maximum velocity (averaged across vessel lumen) during exercise was 9.4±5.7 cm·s-1for the right peroneal vein, 8.5±4.6 cm·s-1for the right posterior tibial vein and 17.8±5.8 cm·s-1for the popliteal vein. The integrated flow volume per exercise (20 s) was 1.9, 1.6 and 50 mL (mean across subjects) for right peroneal, right posterior tibial and popliteal vein, respectively. A patient with DVT presented with peak flow velocities of only about 2 cm·s-1during exercise and less than 1 cm·s-1during rest.
  
  
  CONCLUSIONS
  Real-time PC MRI emerges as a new tool for quantifying the dynamics of muscle-induced flow in deep veins. The method provides both signal intensity changes and velocity information for the assessment of blood flow and muscle movements. It now warrants extended clinical trials to patients with suspected thrombosis.
authors.affiliation: Biomedizinische NMR Forschungs GmbH, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany;; DZHK, German Center for Cardiovascular Research, partner site Göttingen, Germany.
authors.forename: Arun Antony
authors.initials: AA
authors.lastname: Joseph
authors.affiliation: Biomedizinische NMR Forschungs GmbH, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany.
authors.forename: Klaus-Dietmar
authors.initials: KD
authors.lastname: Merboldt
authors.affiliation: Biomedizinische NMR Forschungs GmbH, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Voit
authors.affiliation: Herz & Gefäßzentrum Göttingen am Krankenhaus Neu-Bethlehem, Göttingen, Germany.
authors.forename: Johannes
authors.initials: J
authors.lastname: Dahm
authors.affiliation: Biomedizinische NMR Forschungs GmbH, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany;; DZHK, German Center for Cardiovascular Research, partner site Göttingen, Germany.
authors.forename: Jens
authors.initials: J
authors.lastname: Frahm
keywords: Deep venous flow; phase-contrast MRI; real-time MRI