Diet and gastrointestinal signal on T1-weighted magnetic resonance imaging of mice

In magnetic resonance (MR) imaging of small animals, the gastrointestinal contents may give rise to intense signals on T1-weighted images. The aim of this study was to determine the optimal dietary preparation to reduce gastrointestinal signals in mice and to evaluate the usefulness of this approach. Images of the mouse trunk were obtained using a T1-weighted, three-dimensional fast low-angle shot sequence under various dietary conditions and were compared with respect to the gastrointestinal signals and image quality. The dietary preparation studied included giving alternative diets for 24 h, intestinal cleansing, and 6-h fasting. Mice with and without dietary preparation underwent MR lymphography using gadofluorine 8, and the visualization of abdominal lymph nodes was compared. In the absence of dietary preparation, hyperintense areas were conspicuous in the gastrointestinal system, whereas on the images taken from mice fed potato or sweet potato for 24 h before imaging, gastrointestinal hyperintensity was less prominent. This preparation also reduced artifactual signals and resulted in higher-quality images of the kidneys. Intestinal cleansing, which consisted of 24-h fasting and laxative intake, did not reduce the gastrointestinal signals and caused signal changes that were indicative of fatty liver development. Some of the abdominal lymph nodes of the mice that did not receive dietary preparation were visualized on MR lymphography source images but not on maximum intensity projection (MIP) images. In contrast, on the MIP images of mice fed potato, all the lymph nodes delineated on the source images were successfully visualized. In conclusion, feeding mice potato or sweet potato for 24 h before MR imaging reduces the gastrointestinal signals and image degradation due to artifacts. Appropriate dietary preparations facilitate the display of target structures on MIP images and are expected to enhance the capabilities of small animal MR imaging.     

Autonomous magnetic resonance imaging

Access to Magnetic Resonance Imaging (MRI) across developing countries ranges from being prohibitive to scarcely available. For example, eleven countries in Africa have no scanners. One critical limitation is the absence of skilled manpower required for MRI usage. Some of these challenges can be mitigated using autonomous MRI (AMRI) operation. In this work, we demonstrate AMRI to simplify MRI workflow by separating the required intelligence and user interaction from the acquisition hardware. AMRI consists of three components: user node, cloud and scanner. The user node voice interacts with the user and presents the image reconstructions at the end of the AMRI exam. The cloud generates pulse sequences and performs image reconstructions while the scanner acquires the raw data. An AMRI exam is a custom brain screen protocol comprising of one T₁-, T₂- and T₂*-weighted exams. A neural network is trained to incorporate Intelligent Slice Planning (ISP) at the start of the AMRI exam. A Look Up Table was designed to perform intelligent protocolling by optimizing for contrast value while satisfying signal to noise ratio and acquisition time constraints. Data were acquired from four healthy volunteers for three experiments with different acquisition time constraints to demonstrate standard and self-administered AMRI. The source code is available online. AMRI achieved an average SNR of 22.86 ± 0.89 dB across all experiments with similar contrast. Experiment #3 (33.66% shorter table time than experiment #1) yielded a SNR of 21.84 ± 6.36 dB compared to 23.48 ± 7.95 dB for experiment #1. AMRI can potentially enable multiple scenarios to facilitate rapid prototyping and research and streamline radiological workflow. We believe we have demonstrated the first Autonomous MRI of the brain.     

Time-course magnetic resonance imaging of rat pancreatic cyst after experimental pancreatitis

Fast magnetic resonance (MR) imaging of the rat pancreas was carried out using a snapshot method to observe three-dimensional (3D) and temporal development of the pancreatic cyst after experimental pancreatitis. Acute pancreatitis was induced by a retrograde infusion of the trypsin-taurocholate solution into the pancreatic duct in 23 rats, of which seven survived for one month. Under 2% enflurane anesthesia, (1)H images of the rat abdomen were taken by a 4.7 T magnetic resonance spectrometer under spontaneous breathing. 3D images of the pancreas and cyst were reconstructed from the axial, sagittal and coronal images taken before, 24 h, 7 days, 14 days, 21 days and 28 days after the induction of pancreatitis. The 3D images reconstructed from different slice orientations at each time point showed good agreement with each other. The calculated volumes of the cyst on 7th, 14th, 21st, and 28th day were 0.3 +/- 0.1, 0.8 +/- 0.3, 2.1 +/- 0.6, 6.5 +/- 1.3 mL, respectively. The cystic fluid volume on 28th day was 6.4 +/- 1.4 mL, which confirmed reliability of volume measurement by MR imaging. Fast MR imaging (snapshot) together with 3D reconstruction allows us to understand the detailed chronological and spatial development of pancreatic cyst after acute pancreatitis in rats.     

Feasibility of fat-saturated T2-weighted magnetic resonance imaging with slice encoding for metal artifact correction (SEMAC) at 3T

Background and Purpose

Fluid-sensitive MR imaging in postoperative evaluation is important, however, metallic artifacts is inevitable. The purpose is to investigate the feasibility of fat-saturated slice encoding for metal artifact correction (SEMAC)-corrected T2-weighted magnetic resonance (MR) at 3T in patients with spinal prostheses.

Methods

Following institutional review board approval, 27 SEMAC-encoded spinal MRs between September 2012 and October 2013 in patients with spinal metallic prostheses were analyzed. The MR images were scanned on a 3T MR system including SEMAC-corrected and uncorrected fast spin echo (FSE) T2-weighted MR images with fat-saturation. Two musculoskeletal radiologists compared the image sets and qualitatively analyzed the images using a five-point scale in terms of artifact reduction around the prosthesis, visualization of the prosthesis and pedicle, and intervertebral neural foramina. Quantitative assessments were performed by calculating the ratio of signal intensity from the fixated vertebra and that from upper level vertebra. For statistical analyses, paired t-test was used.

Results

Fat-saturated SEMAC-corrected T2-weighted MR images enabled significantly improved metallic artifact reduction (P < 0.05). Quantitative evaluation of the signal intensity ratio of screw-fixated vertebra and upper level vertebra showed a significantly lower ratio on fat-saturated SEMAC images (P < 0.05), however, the high signal intensity of signal pile-up could be not completely corrected.

Conclusion

SEMAC correction in fat-suppressed T2-weighted MR images can overcome the signal loss of metallic artifacts and provide improved delineation of the pedicle screw and peri-prosthetic region. Signal pile-up, however, could not be corrected completely, therefore readers should be cautious in the evaluation of marrow around the prosthesis.     

Detection of focal liver lesions in unenhanced and ferucarbotran-enhanced magnetic resonance imaging: a comparison of T2-weighted breath-hold and respiratory-triggered sequences

Purpose

To investigate the image quality and detection rate of focal liver lesions by comparing a T2-weighted breath-hold single-shot sequence and a T2-weighted high spatial resolution fast spin-echo sequence with respiratory triggering via unenhanced and superparamagnetic iron oxide (SPIO)-enhanced liver imaging.

Materials and Methods

The study was approved by the local ethical review board; informed consent was waived. Liver-lesion contrast was measured and a qualitative consensus evaluation of image quality and lesion detection was performed in 42 consecutive patients using a 1.5-T MR system.

Results

The liver-lesion contrast was significantly higher (P<.05) for the respiratory-triggered sequence compared to the breath-hold sequence regarding unenhanced and SPIO-enhanced imaging. The respiratory-triggered sequences revealed significantly higher image quality scores as well as higher numbers of detected liver lesions compared to the breath-hold sequence on unenhanced and SPIO-enhanced imaging. The SPIO contrast did not significantly improve the number of detected lesions on the respective sequences (P>.05).

Conclusion

We find that respiratory-triggered fast spin-echo sequences produce a higher image quality and a more precise liver-lesion detection rate thereby justifying the increased acquisition time necessary for this method.     

Proton magnetic resonance imaging and phosphorus-31 magnetic resonance spectroscopy studies of bromobenzene-induced liver damage in the rat.

Respiratory-gated proton magnetic resonance imaging was used to study the response of the rat liver in situ to bromobenzene, a classic hepatotoxicant. A localized region of high proton signal intensity in the perihilar region of the liver was seen 24-48 hr after an intraperitoneal injection of bromobenzene. Localized proton magnetic resonance spectra from within this region indicated that the increased proton signal intensity was not due to accumulation of fat in the liver, but primarily due to a longer T2 for the proton resonance of water. This is consistent with acute edema in this localized region. In vivo 31P magnetic resonance spectroscopy studies of the same rat livers in situ were performed. Spectroscopic conditions were determined whereby localized, quantitative 31P spectra could be obtained. Using these methods, 10 mmol/kg bromobenzene was found after 24 hr to cause a number of statistically significant (p less than 0.05) effects: a decrease in adenosine 5'-triphosphate levels from 4.1 +/- 0.5 to 3.0 +/- 0.5 mM, a decrease in phosphodiester levels from 11.3 +/- 0.9 to 9.3 +/- 0.7 mM and an increase in the phosphomonoesters from 3.0 +/- 0.4 to 5.5 +/- 1.2 mM (mean +/- standard deviation). High resolution in vitro 31P spectra of perchloric acid extracts of these rat livers showed that the increased phosphomonoester resonance was due to a selective 4.3-fold increase in phosphocholine. Thus, our in vivo and in vitro 31P magnetic resonance spectra are consistent with the hypothesis that a phosphatidylcholine-specific phospholipase C (generating phosphocholine and diacylglycerol) is activated during tissue damage. Both the imaging and spectroscopy results obtained with bromobenzene closely resemble CCl4-induced liver changes previously reported, and may reflect a generalized response of the liver to any acutely acting toxic chemical.     

Current-induced magnetic resonance phase imaging

Electric current-induced phase alternations have been imaged by fast magnetic resonance image (MRI) technology. We measured the magnetic resonance phase images induced by pulsed current stimulation from a phantom and detected its sensitivity. The pulsed current-induced phase image demonstrated the feasibility to detect phase changes of the proton magnetic resonance signal that could mimic neuronal firing. At the present experimental setting, a magnetic field strength change of 1.7 +/- 0.3 nT can be detected. We also calculated the averaged value of the magnetic flux density BT parallel to B0 produced by electric current I inside the voxel as a function of the wire position. The results of the calculation were consistent with our observation that for the same experimental setting the current-induced phase change could vary with location of the wire inside the voxel. We discuss our findings in terms of possible direct MRI detection of neuronal activity.     

Detection of freeze injury in oranges by magnetic resonance imaging of moving samples

Magnetic resonance imaging (MRI) is applied for on-line inspection of fruits. The aim of this work is to address the applicability of MRI for freeze injury detection in oranges directly on a distribution chain. Undamaged and damaged oranges are conveyed at 50 and 100 mm/s by a specially designed conveyor within a 4.7 T spectrometer obtaining fast low-angle shot images. An automatic segmentation algorithm is proposed that allows the discrimination between undamaged and damaged oranges.     

Fast field-cycling magnetic resonance imaging

Magnetic resonance imaging (MRI) and fast field-cycling (FFC) NMR are both well-developed methods. The combination of these techniques, namely fast field-cycling magnetic resonance imaging (FFC-MRI) is much less well-known. Nevertheless, FFC-MRI has a number of significant applications and advantages over conventional techniques, and is being pursued in a number of laboratories. This article reviews the progress in FFC-MRI over the last two decades, particularly in the areas of Earth's field and pre-polarised MRI, as well as free radical imaging using field-cycling Overhauser MRI. Different approaches to magnet design for FFC-MRI are also described. The paper then goes on to discuss recent techniques and applications of FFC-MRI, including protein measurement via quadrupolar cross-relaxation, contrast agent studies, localised relaxometry and FFC-MRI with magnetisation-transfer contrast.     

Ex vivo magnetic resonance imaging of rat spinal cord at 9.4 T

The magnetic resonance (MR) properties of the rat spinal cord were characterized at the T9 level with ex vivo experiments performed at 9.4 T. The inherent endogenous contrast parameters, proton density (PD), longitudinal and transverse relaxation times T1 and T2, and magnetization transfer ratio (MTR) were measured separately for the grey matter (GM) and white matter (WM). Analysis of the measurements indicated that these tissues have statistically different proton densities with means PD(GM)=54.8+/-2.5% versus PD(WM)=45.2+/-2.4%, and different T1 values with means T1GM=2.28+/-0.23 s versus T1WM=1.97+/-0.21 s. The corresponding values for T2 were T2GM=31.8+/-4.9 ms versus T2WM=29.5+/-4.9 ms, and the difference was insignificant. The difference between MTR(GM)=31.2+/-6.1% and MTR(WM)=33.1+/-5.9% was also insignificant. These results collectively suggest that PD and T1 are the two most important parameters that determine the observed contrast on spinal cord images acquired at 9.4 T. Therefore, in MR imaging studies of spinal cord at this field strength, these parameters need to be considered not only in optimizing the protocols but also in signal enhancement strategies involving exogenous contrast agents.     

170 nm nuclear magnetic resonance imaging using magnetic resonance force microscopy

We demonstrate one-dimensional nuclear magnetic resonance imaging of the semiconductor GaAs with 170 nm slice separation and resolve two regions of reduced nuclear spin polarization density separated by only 500 nm. This was achieved by force detection of the magnetic resonance, magnetic resonance force microscopy (MRFM), in combination with optical pumping to increase the nuclear spin polarization. Optical pumping of the GaAs created spin polarization up to 12 times larger than the thermal nuclear spin polarization at 5K and 4T. The experiment was sensitive to sample volumes of 50 microm(3) containing approximately 4 x 10(11)71 Ga/Hz. These results demonstrate the ability of force-detected magnetic resonance to apply magnetic resonance imaging to semiconductor devices and other nanostructures.     

核磁共振成像系列实验教学探讨

超小型核磁共振成像仪已经应用在近代物理实验教学中,该仪器可以研究各种样品的脉冲核磁共振.本文从教学内容和教学方法上对核磁共振成像实验进行了探讨·     

Cardiovascular applications of magnetic resonance imaging

Magnetic resonance imaging (MRI) is a completely noninvasive modality that has shown significant promise for the evaluation of the cardiovascular system. Our imaging technique employed electrocardiographic (ECG) gating, which resulted in well-resolved images of the cardiac structures. Patients and animals with a variety of cardiovascular abnormalities were also assessed with this technique; the abnormalities included acute and remote myocardial infarctions and their sequelae, atherosclerotic plaques, hypertrophic cardiomyopathy, pericardial diseases, and aneurysms. The diagnostic utility of MRI includes direct tissue characterization, and such utility may be further extended by the use of paramagnetic contrast media. In addition, metabolic imaging of elements other than hydrogen may further increase the clinical potential of MRI for assessment of the cardiovascular system.