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Martin Rohrer

Publications and source records attributed to Martin Rohrer.

4 recordsLinked to original sources
PubMed2006

Effects of injection rate and dose on image quality in time-resolved magnetic resonance angiography (MRA) by using 1.0M contrast agents.

In time-resolved MRA (TR MRA), injection parameters and contrast agent (CA) dose are important factors influencing image quality. In this study, three different injection schemes with different CA volumes were evaluated in 12 healthy volunteers. Injection rates between 0.2 and 0.8 ml/s were evaluated with CA volumes of 10 and 20 ml. To measure circulatory parameters, cine cardiac MRI was performed before each exam. Spatial resolution could be reduced to 2 x 1.4 x 2 mm3, temporal resolution was 2.25 s/frame. To exclude signal saturation at high CA concentrations, a phantom with fixed CA concentrations was placed in the field of view. SNR was measured, and the area under the curve of the arterial signal of the different injection schemes was calculated. Results showed the largest diagnostic window at a relatively slow injection rate of 0.4 ml/s and a CA volume of 10 ml. Circulatory parameters have an important impact on CA arrival, so delay times have to be set depending on these parameters.

Adult↗
PubMed2006

Initial imaging recommendations for Vasovist angiography.

Vasovist is a newly developed blood pool contrast agent for MR angiogiography (MRA). It consists of a low molecular weight molecule, chelated to Gadolinium, that strongly binds to plasma proteins, thus increasing its relaxivity and retention time in the vascular system. Due to its high efficiency, a smaller dose compared to existing Extracellular Fluid Contrast Agents is sufficient for diagnostic purposes, resulting in a lower injection volume. With appropriate adjustments of standard extracellular contrast injection protocols, a dynamic phase MRA can be achieved using routine MRA parameters. For extended phase imaging, ('steady-state') starting approximately 3 to 5 min post injection, repetition time (TR) and flip angle may be adjusted for optimization of intravascular signal. Preliminary technical recommendations for the optimization of contrast-enhanced MRA with Vasovist can be deducted from current clinical trial experience in various vessel beds.

Contrast Media↗
PubMed2005

Comparison of magnetic properties of MRI contrast media solutions at different magnetic field strengths.

RATIONALE AND OBJECTIVES: To characterize and compare commercially available contrast media (CM) for magnetic resonance imaging (MRI) in terms of their relaxivity at magnetic field strengths ranging from 0.47 T to 4.7 T at physiological temperatures in water and in plasma. Relaxivities also were quantified in whole blood at 1.5 T. METHODS: Relaxivities of MRI-CM were determined by nuclear magnetic resonance (NMR) spectroscopy at 0.47 T and MRI phantom measurements at 1.5 T, 3 T, and 4.7 T, respectively. Both longitudinal (T1) and transverse relaxation times (T2) were measured by appropriate spin-echo sequences. Nuclear magnetic resonance dispersion (NMRD) profiles were also determined for all agents in water and in plasma. RESULTS: Significant dependencies of relaxivities on the field strength and solvents were quantified. Protein binding leads to both increased field strength and solvent dependencies and hence to significantly altered T1 relaxivity values at higher magnetic field strengths. CONCLUSIONS: Awareness of the field strength and solvent associated with relaxivity data is crucial for the comparison and evaluation of relaxivity values. Data observed at 0.47 T can thus be misleading and should be replaced by relaxivities measured at 1.5 T and at 3 T in plasma at physiological temperature.

Contrast Media↗