Biomedical subjects

Reed F Busse

Publications and source records attributed to Reed F Busse.

7 recordsLinked to original sources

PubMed2006

Fast spin echo sequences with very long echo trains: design of variable refocusing flip angle schedules and generation of clinical T2 contrast.

Reducing and continuously varying the flip angle of the refocusing RF pulses in a rapid acquisition with relaxation enhancement (RARE; fast/turbo spin echo) sequence is a useful means of addressing high RF power deposition and modulation transfer function (MTF) distortion due to relaxation. This work presents a streamlined technique to generate a sequence of refocusing flip angles on a per-prescription basis that produces relatively high SNR and limits blurring in a wide range of materials encountered in vivo. Since the "effective TE" (traditionally defined as the time at which the center of k-space is sampled) no longer corresponds to the expected amount of spin-echo T2 contrast due to the mixing of stimulated and spin echoes, a "contrast-equivalent" TE is defined and experimentally demonstrated that allows annotation of a more accurate effective TE that matches the contrast produced by 180 degrees refocusing. Furthermore, contrast is shown to be manipulable by the addition of magnetization preparation pulse sequence segments, such as T2-prep, to produce clinically desirable contrast for routine head and body imaging.

Algorithms↗

PubMed2006

Noninvasive oxygen partial pressure measurement of human body fluids in vivo using magnetic resonance imaging.

RATIONALE AND OBJECTIVES: The oxygen partial pressure (pO2) of human body fluids reflects the oxygenation status of surrounding tissues. All existing fluid pO2 measurements are invasive, requiring either microelectrode/optode placement or fluid removal. The purpose of this study is to develop a noninvasive magnetic resonance imaging method to measure the pO2 of human body fluids. MATERIALS AND METHODS: We developed an imaging paradigm that exploits the paramagnetism of molecular oxygen to create quantitative images of fluid oxygenation. A single-shot fast spin echo pulse sequence was modified to minimize artifacts from motion, fluid flow, and partial volume. Longitudinal relaxation rate (R1 = 1/T1) was measured with a time-efficient nonequilibrium saturation recovery method and correlated with pO2 measured in phantoms. RESULTS: pO2 images of human and fetal cerebrospinal fluid, bladder urine, and vitreous humor are presented and quantitative oxygenation levels are compared with prior literature estimates, where available. Significant pO2 increases are shown in cerebrospinal fluid and vitreous following 100% oxygen inhalation. Potential errors due to temperature, fluid flow, and partial volume are discussed. CONCLUSIONS: Noninvasive measurements of human body fluid pO2 in vivo are presented, which yield reasonable values based on prior literature estimates. This rapid imaging-based measurement of fluid oxygenation may provide insight into normal physiology as well as changes due to disease or during treatment.

Adult↗

PubMed2006

Evaluation of real-time single-shot fast spin-echo MRI for visualization of the fetal midline corpus callosum and secondary palate.

OBJECTIVE: The objective of our study was to assess the visibility of the fetal corpus callosum and soft palate on standard single-shot fast spin-echo (SSFSE) imaging versus real-time (RT) SSFSE imaging. SUBJECTS AND METHODS: Part 1 of the study was a prospective analysis using a questionnaire rating the ease of use and utility of RT imaging. Part 2 of the study was a retrospective analysis of 69 fetal MRI studies with RT sagittal midline imaging of the head, face, or both. Standard and RT SSFSE image sets were de-identified, randomized, and shown to three pediatric neuroradiologists who rated on a 5-point scale whether the images were midline and how well they could see and characterize as normal the corpus callosum and secondary palate. The imaging results were correlated with postnatal diagnosis. Statistical methods included the Wilcoxon's signed rank test, McNemar chi-square test, and analysis of variance. RESULTS: Prospectively, the RT SSFSE technique was ranked as excellent in all the categories assessed. Retrospective analysis showed that the midline view obtained with RT SSFSE imaging was helpful in diagnosing the normal and abnormal secondary palate, allowing improved diagnosis of 19 (30.6%) of 62 cases of normal palate and four (57.1%) of seven cases of abnormal palate, when compared with the standard SSFSE technique. RT SSFSE imaging improved the ability to diagnose a normal corpus callosum on the midline view in 13 (27.6%) of 47 fetuses of 20 or more weeks gestational age. CONCLUSION: The RT SSFSE technique can aid in obtaining images in planes that are critical to the evaluation of a moving fetus, particularly when a midline sagittal view of the corpus callosum or palate is required. The use of this technique may lead to improved diagnosis of CNS or orofacial abnormalities in fetuses.

Corpus Callosum↗

PubMed2005

Flip angle calculation for consistent contrast in spoiled gradient echo imaging.

In spoiled gradient echo sequences, the T(1)-weighting of image contrast is strongly affected by a nonlinear interaction of two sequence parameters, repetition time (TR) and flip angle (alpha). If alpha is not properly adjusted to compensate for variation in TR due to changing resolution, bandwidth, or number of slices, any optimization of contrast-to-noise may be compromised. Currently, there is no direct way to compare or reproduce the contrast properties of one sequence to another with a different TR. Here, it is demonstrated that for short TRs alpha may be calculated and automatically adjusted such that relative contrast--the shape of the signal-versus-T(1) curve--remains consistent and signal scales proportionally to radicalTR in all tissues. TR is then free to vary to accommodate a range of sequence parameters without impacting relative contrast and the T(1)-weighting of one sequence can be compared to, or reproduced in, another study with a different TR.

Abdomen↗

PubMed2005

Real-time magnetic resonance imaging aids prenatal diagnosis of isolated cleft palate.

OBJECTIVE: Cleft of the secondary palate without cleft lip is difficult to visualize sonographically. This study was performed to assess the utility of sonography, standard magnetic resonance (MR) imaging, and real-time MR imaging in the diagnosis of isolated cleft palate. METHODS: We prospectively assessed 5 fetuses at risk for isolated cleft palate on the basis of family history, micrognathia, or both, using sonography and standard and real-time single-shot fast spin echo MR sequences. Written informed consent was obtained under our Institutional Review Board-approved Health Insurance Portability and Accountability Act-compliant protocol. Images were assessed for confidence in a diagnosis of cleft or normal palate. Prenatal and postnatal diagnoses were compared. RESULTS: In 3 fetuses, micrognathia was visualized by sonography and MR imaging with standard and real-time sequences. One fetus at 19 weeks had a wide cleft of the entire secondary palate, and another fetus at 33 weeks had a cleft of the soft palate; these defects were seen only with real-time MR imaging. One 35-week gestational age fetus had a cleft soft palate that was visualized on standard and real-time MR imaging. Two fetuses with no abnormalities had the normal midline secondary palate seen only on real-time MR imaging. In all fetuses, real-time images were helpful in assessing the secondary palate because the entire midline naso-oropharynx could be visualized. CONCLUSIONS: Real-time MR imaging allows for rapid assessment of the midline structures, providing accurate diagnosis of isolated cleft palate.

Cleft Palate↗

PubMed2005

Fetal magnetic resonance imaging in the evaluation of fetuses referred for sonographically suspected abnormalities of the corpus callosum.

OBJECTIVE: Fetal magnetic resonance imaging (MRI) has been shown to be useful in assessing the developing central nervous system. However, its utility in specific brain disorders has not been well investigated. We hypothesized that fetal MRI can better assess the integrity of the brain in cases with sonographically suspected callosal abnormalities. METHODS: We retrospectively reviewed fetal MRI and prenatal sonographic studies of 10 fetuses referred for MRI for sonographically suspected callosal abnormalities. RESULTS: An abnormal corpus callosum was identified on fetal MRI in 80% of cases. The type of callosal abnormality (complete or partial agenesis) was similar on both prenatal sonography and fetal MRI in all cases. All sonographically identified additional brain abnormalities were detected on fetal MRI, with the exception of choroid plexus cysts. Furthermore, in 63% (5 of 8) of cases with a callosal abnormality on both sonography and fetal MRI, additional brain abnormalities were detected on fetal MRI that were not apparent on sonography. These sonographically occult findings were confirmed on postnatal MRI or autopsy in 3 of 5 patients. CONCLUSIONS: Fetal MRI is an important adjunct to sonography in assessing the corpus callosum and other aspects of brain development when agenesis of the corpus callosum is suspected. It can identify frequent additional findings that are not visible on sonography such as abnormal sulcation. In light of the association between additional brain abnormalities and worse neurodevelopmental outcome, the potential of fetal MRI as an important adjunctive prognostic imaging test in fetuses with callosal agenesis can now be tested.

Agenesis of Corpus Callosum↗

PubMed2004

Reduced RF power without blurring: correcting for modulation of refocusing flip angle in FSE sequences.

In order to reduce the RF power deposition of fast spin echo sequences operated at high field strength, the flip angles of the refocusing pulse train are varied from pulse to pulse using a modulated angle refocusing train method. The technique employs high flip angle pulses prior to sampling the center of k-space in order to preserve T(2) contrast, low flip angles after sampling the center of k-space to reduce power and prolong relaxation, and a smooth transition between the high and low flip angle regimes in order to maintain the pseudosteady-state, maximizing signal and avoiding artifact-inducing oscillations. An analytical expression is used to predict and correct for the flip angle dependence of the signal, thus eliminating any deleterious effects of flip angle modulation on the point spread function. Analysis of resolution and SNR were performed in simulation and phantom studies. In human imaging studies, it is shown that RF energy deposition per slice in a single-shot fast spin echo application can be reduced by up to 75%, making the sequence as practical at 3 T as it is has been at 1.5 T.

Humans↗