Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine
-
Bone metastases of 16 prostate cancer patients were scanned twice 1 week apart by dynamic contrast enhanced (DCE)-MRI at 2-s resolution using a two-dimensional gradient-echo pulse sequence. With a multiple reference tissue method (MRTM), the local tissue arterial input function (AIF) was estimated using the contrast agent enhancement data from tumor subregions and muscle. ⋯ The individual MRTM AIFs were also used to obtain a mean local tissue AIF for the unique population of this study, which further improved the reproducibility of the estimated kinetic parameters. The MRTM can be applied to DCE-MRI studies of bone metastases from prostate cancers to provide an AIF from which reproducible quantitative DCE-MRI parameters can be derived, thus help standardize DCE-MRI studies in cancer patients.
-
Real-time geometric distortion correction for interventional imaging with echo-planar imaging (EPI).
Many MR-guided interventional procedures rely on fast imaging sequences for providing images in real-time with a precise relation between the target position in the image and its true position. Echo-planar imaging (EPI) methods are very fast but prone to geometric distortions. ⋯ The method is demonstrated with MR-thermometry for guiding thermal therapies. The proposed approach imposes a small penalty in acquisition speed but adds negligible latency to data processing, an important element for interventions of mobile organs.
-
We investigated the biophysical mechanism of low-frequency drift in blood-oxygen-level-dependent (BOLD) functional magnetic resonance imaging (fMRI) (0.00-0.01 Hz), by exploring its spatial distribution, dependence on imaging parameters, and relationship with task-induced brain activation. Cardiac and respiratory signals were concurrently recorded during MRI scanning and subsequently removed from MRI data. It was found that the spatial distribution of low-frequency drifts in human brain followed a tissue-specific pattern, with greater drift magnitude in the gray matter than in white matter. ⋯ In fMRI studies with visual stimulation, a strong positive correlation between drift effects at baseline and task-induced BOLD signal changes was observed both across subjects and across activated pixels within individual participants. We further demonstrated that intrinsic, physiological drift effects are a major component of the spontaneous fluctuations of BOLD fMRI signal within the frequency range of 0.0-0.1 Hz. Our study supports brain physiology, as opposed to scanner instabilities or cardiac/respiratory pulsations, as the main source of low-frequency drifts in BOLD fMRI.