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Technical parameters affecting image characteristics in in vivo MR microscopy of the mouse
Kazutaka Yamada1, Erik R Wisner, Jeff S de Ropp
1Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
Abstract:
The aim of the study was to assess the effects of changing acquisition parameters used for high-resolution in vivo magnetic resonance (MR) microscopy on image quality and scan time. The head or abdomen of 11 normal and 1 glioblastoma-bearing anesthetized BALB/c mice were imaged using a high-resolution 7.0-Tesla magnet. Scan parameters such as matrix size (MTX), slice thickness (ST), number of excitations (NEX), pulse sequence type including repetition time (TR) and echo time (TE), respiratory gating, and intraperitoneal contrast medium administration were altered to assess their actual effect on signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) as compared to calculated effects. As expected, SNR increased with increasing ST or NEX and with decreasing MTX. However, although the empirical increase in SNR was similar to that expected for increased ST, it was less than that anticipated for increasing NEX or decreasing MTX. Increasing NEX and applying respiratory gating both increased SNR and reduced the image degradation associated with respiratory motion in images of the abdomen. Intraperitoneal contrast medium administration produced a marked increase in CNR in the subject with the implanted glioblastoma, suggesting that this route is satisfactory for the enhancement of lesions disrupting the blood-brain barrier. The consequence of improving image quality in terms of spatial and contrast resolution is increased scan time. However, the actual increase in SNR when altering acquisition parameters may not be as much as predicted by theory.
Insights
Optimizing magnetic resonance (MR) microscopy involves adjusting parameters like matrix size and excitations. While these changes improve signal-to-noise ratio (SNR), the actual gains may differ from theoretical predictions, impacting scan time.
Area of Science:
- Medical Imaging
- Biophysics
Background:
- High-resolution in vivo magnetic resonance (MR) microscopy is crucial for preclinical research.
- Understanding the impact of acquisition parameters on image quality and scan time is essential for optimizing MR microscopy protocols.
Purpose of the Study:
- To evaluate how modifications in MR microscopy acquisition parameters affect image quality (signal-to-noise ratio [SNR] and contrast-to-noise ratio [CNR]) and scan duration.
- To compare the experimentally observed effects of parameter changes with theoretically predicted outcomes.
Main Methods:
- Utilized a 7.0-Tesla magnet to image the heads and abdomens of 12 anesthetized BALB/c mice (11 normal, 1 glioblastoma-bearing).
- Systematically altered acquisition parameters: matrix size (MTX), slice thickness (ST), number of excitations (NEX), pulse sequence (TR/TE), respiratory gating, and contrast agent administration.
- Quantified changes in SNR and CNR relative to theoretical calculations.
Main Results:
- Increased ST and NEX, and decreased MTX, generally led to higher SNR, though empirical increases sometimes deviated from theoretical expectations.
- Respiratory gating and increased NEX effectively improved SNR and reduced motion artifacts in abdominal imaging.
- Intraperitoneal contrast administration significantly enhanced CNR in the glioblastoma model, indicating efficacy for detecting blood-brain barrier disruptions.
Conclusions:
- Acquisition parameter adjustments in MR microscopy influence image quality and scan time, with empirical results sometimes differing from theoretical predictions.
- Respiratory gating and optimized NEX are valuable for improving image quality in abdominal MR microscopy.
- Intraperitoneal contrast is effective for enhancing glioblastoma visualization in vivo.