Biomedical subjects

Steffen Volz

Publications and source records attributed to Steffen Volz.

5 recordsLinked to original sources

PubMed2004

MR-guided intravascular procedures: real-time parameter control and automated slice positioning with active tracking coils.

PURPOSE: To implement and optimize a real-time pulse sequence and user interface to perform intravascular interventions using active catheter tracking. MATERIALS AND METHODS: In magnetic resonance (MR)-guided interventions, small radio-frequency coils can be used to rapidly determine the device position (active tracking). In this work, active catheter tracking was combined with a dedicated real-time pulse sequence and user interface. The pulse sequence offered the imaging contrasts fast low angle shot (FLASH), true Fast imaging with steady state precession (TrueFISP), and projection MR digital subtraction angiography (MR-DSA), which could be selected by the radiologist from within the scanner room at any time during the intervention. Automatic slice positioning was added to the real-time pulse sequence so that the location of the tracking coils defined the image slice position and orientation. The technique was assessed in phantoms and animal experiments. RESULTS: At a reaction time of 24 msec and a frame rate of three images per second, the movement of an active intravascular catheter could be monitored in the aorta and the renal arteries of a pig. With interactive contrast and orientation changes, the renal vasculature could be assessed by a fully MR-guided catheterization in less than 10 minutes. CONCLUSION: With carefully designed active catheters, a dedicated user interface, and an optimized pulse sequence intravascular interventions can successfully be performed by a single operator from within the MR scanner room.

Animals↗

PubMed2004

MR coil design for simultaneous tip tracking and curvature delineation of a catheter.

In active catheter tracking, small RF coils are attached to the catheter for localization. For interactive catheter steering at vessel branchings, it is necessary to visualize not only a single point near the catheter tip but also the entire shape and orientation of the catheter's distal end. Therefore, a 35-mm-long twisted-pair RF coil was added to a 5 French intravascular catheter with a single tip-tracking coil. With the use of small nonmagnetic electronic components at the catheter tip, and a special switching circuitry outside the catheter, the coil assembly could be operated in two different modes. During MRI, the tip-tracking coil was detuned so that the MR signal was received by the visualization coil only. During tracking, detuning was switched off and the MR signal was predominantly received by the more sensitive tracking coil. The catheter was used in combination with a MR pulse sequence with automatic slice positioning so that the current imaging slice was always placed at the position of the catheter tip. Phantom and animal experiments showed that the catheter tip is better visualized with the combined approach than with a tracking coil alone.

Animals↗

PubMed2004

Semiquantitative fast flow velocity measurements using catheter coils with a limited sensitivity profile.

Flow measurements can be used to quantify blood flow during MR-guided intravascular interventional procedures. In this study, a fast flow measurement technique is proposed that quantifies flow velocities in the vicinity of a small RF coil attached to an intravascular catheter. Since the small RF coil receives signal from only a limited volume around the catheter, a spatially nonselective signal reception is employed. To enhance signal from flowing blood, and suppress unwanted signal contributions from static material, a slice-selective RF excitation is used. At a velocity sensitivity of 150 cm/s, a temporal resolution of 2 x TR = 10.2 ms can be achieved. The flow measurement is combined with an automatic slice positioning to facilitate measurements during interventional procedures. The influence of the catheter position in the blood vessel on the velocity measurement was analyzed in simulations. For blood vessels with laminar flow, the simulation showed a systematic deviation between catheter measurement and true flow between -15% and 80%. In four animal experiments, the catheter velocity measurement was compared with results from a conventional ECG-triggered 2D phase-contrast (PC) technique. The shapes of the velocity time curves in the abdominal aorta were nearly identical to the conventional measurements. A relative scaling factor of 0.69-1.19 was found between the catheter velocity measurement and the reference measurement, which could be partly explained by the simulation results.

Animals↗

PubMed2004

Renal embolization: feasibility of magnetic resonance-guidance using active catheter tracking and intraarterial magnetic resonance angiography.

RATIONALE AND OBJECTIVES: Magnetic resonance (MR)-guidance of endovascular interventions offers various advantages, including the absence of ionizing radiation, excellent soft tissue contrast, and multiplanar and functional imaging capabilities. The objective of this study was to assess the feasibility of MR-guided renal embolization using active catheter tracking with automatic slice positioning and intraarterial contrast-enhanced MR angiography (MRA). MATERIALS AND METHODS: MR-guided embolization of 16 kidneys was attempted in 15 pigs using real-time tracking of active 5-Fr. catheters. Embolization was monitored by selective intraarterial projection MRA. Intraarterial three-dimensional (3D) MRA was used for the assessment of embolization results. Additional pathologic correlation was available in 2 animals. The image quality of intraarterial 3D contrast-enhanced-MRA was rated by an independent radiologist who was not involved in the animal experiments. RESULTS: Active catheter tracking with automatic slice positioning allowed reliable catheter guidance and catheterization of the renal artery in all animals. Embolization was successful in all kidneys (11 left, 5 right), as verified by intraarterial 3D contrast-enhanced MRA (ce-MRA) and/or pathology. The image quality of intraarterial 3D ce-MRA was rated excellent in 10 animals, moderate in 4 animals, and poor in 1 animal. CONCLUSION: Renal embolization using active catheter tracking and intraarterial ce-MRA is feasible. Selective intraarterial ce-MRA allows the assessment of blood supply and organ perfusion before, during, and after therapeutic interventions, thereby complementing MR-guided endovascular interventions.

Animals↗

PubMed2003

[Automatic slice tracking in interventional magnetic resonance imaging].

Magnetic resonance imaging (MRI) is ideally suited to monitor minimally invasive operations with catheters or needles, since it offers both a superior soft-tissue contrast and the possibility to perform functional tests. In the present study, small radio-frequency coils were attached to the instruments in order to localize the MR-invisible instruments. The implementation of active instrument tracking is described on the basis of the example of active catheter tracking. In this case, the current position information of the instrument is used to automatically position the MRI slice at the catheter location. In combination with a user interface, the interventional radiologist is offered the possibility to perform vascular interventions from within the MR scanner room. At image update rates of approximately 3 Hz, tracking and placement of catheters in vascular structures are possible with interactive switching of slice orientation and image contrast. In an animal model, the technique was successfully used to selectively visualize the abdominal vessels and their branches under MRI guidance.

Animals↗