Use of hyperpolarized ¹³C in magnetic resonance (MR) imaging is a new technique that enhances signal tens of thousands-fold. Recent in vivo animal studies of metabolic imaging that used hyperpolarized ¹³C demonstrated its potential in many applications for disease indication, metabolic profiling, and treatment monitoring. We review the basic physics for dynamic nuclear polarization (DNP) and in vivo studies reported in prostate cancer research, hepatocellular carcinoma research, diabetes and cardiac applications, brain metabolism, and treatment response as well as investigations of various DNP ¹³C substrates.

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Purpose: We investigated the spatiotemporal changes in signal in draining lymph nodes of mice to ascertain the size-dependent effects of variously sized particles of iron oxide used to enhance magnetic resonance (MR) lymphography.
Materials and Methods: We injected iron oxide particles of 50-, 100-, 200-, or 1,000-nm diameter into the footpads of individual mice and obtained sequential MR images of the popliteal and inguinal lymph nodes with 11.7 tesla up to 6 weeks after particle administration.
Results: Up to 30 min after administration of particles smaller than 100 nm, we observed a marked reduction in signal in the popliteal node that spread from the periphery at first observation toward the center of the node in subsequent measurements and persisted up to 6 weeks. In contrast, 1,000-nm particles caused dot-like areas of hypointensity in the popliteal lymph node, primarily in the inner portion, that appeared after 2 days. In the inguinal lymph nodes, signal changes occurred after 2 days for 50- and 100-nm particles and after one week for 1,000-nm particles. For 1,000-nm particles, areas of hypointensity were visible in the inner portion and not the periphery of the inguinal lymph node up to 6 weeks. In this study, we demonstrate the strong dependence of MR imaging contrast in draining lymph nodes on the size of the particle-shaped contrast agents injected subcutaneously. Particle size represented passive and active targeting effects, so micron-sized particles produced delayed enhancement.
Conclusion: Choosing the size of iron oxide particles for MR imaging contrast depends on the objective of observation, such as identifying the morphology or migration of immune cells in the lymph node.

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Purpose: Multiple small-animal magnetic resonance (MR) imaging to measure tumor volume may increase the throughput of preclinical cancer research assessing tumor response to novel therapies. We used a clinical scanner and multi-channel coil to evaluate the usefulness of this imaging to assess experimental tumor volume in mice.
Methods: We performed a phantom study to assess 2-dimensional (2D) geometric distortion using 9-cm spherical and 32-cell (8×4 one-cm² grids) phantoms using a 3-tesla clinical MR scanner and dedicated multi-channel coil composed of 16 5-cm circular coils. Employing the multi-channel coil, we simultaneously scanned 6 or 8 mice bearing sarcoma 180 tumors. We estimated tumor volume from the sum of the product of tumor area and slice thickness on 2D spin-echo images (repetition time/echo time, 3500/16 ms; in-plane resolution, 0.195×0.195×1 mm³). After MR acquisition, we excised and weighed tumors, calculated reference tumor volumes from actual tumor weight assuming a density of 1.05 g/cm³, and assessed the correlation between the estimated and reference volumes using Pearson's test.
Results: Two-dimensional geometric distortion was acceptable below 5% in the 9-cm spherical phantom and in every cell in the 32-cell phantom. We scanned up to 8 mice simultaneously using the multi-channel coil and found 11 tumors larger than 0.1 g in 12 mice. Tumor volumes were 1.04±0.73 estimated by MR imaging and 1.04±0.80 cm³ by reference volume (average±standard deviation) and highly correlated (correlation coefficient, 0.995; P<0.01, Pearson's test).
Conclusion: Use of multiple small-animal MR imaging employing a clinical scanner and multi-channel coil enabled accurate assessment of experimental tumor volume in a large number of mice and may facilitate high throughput monitoring of tumor response to therapy in preclinical research.

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Purpose: To maximize the extent of tumor resection and minimize postoperative neurological deficits in patients with brain neoplasms, it is very important to evaluate the integrity of the corticospinal tract (CST) before surgery. We attempted to determine whether CST abnormality in these patients correlates with clinical motor weakness.
Methods: We retrospectively evaluated 19 patients (16 men, 3 women, aged 39 to 70 years) with pathologically proven brain neoplasms with lesions adjacent to the posterior limb of the internal capsule and categorized their motor function as normal or abnormal based on clinical assessment. After correcting raw diffusion tensor image (DTI) data for motion and eddy-current artifacts, we computed fractional anisotropy (FA) and apparent diffusion coefficient (ADC) maps. We manually segmented the CST from the level of the cerebral peduncle to the internal capsule, used the segmented CST as the mask for FA and ADC measurements, and compared normalized FA (nFA) and ADC (nADC) values relative to the contralateral normal side using a 2-tailed, unpaired t-test.
Results: Compared with the normalized values for patients with normal motor function, patients with abnormal motor function demonstrated significantly decreased FA (P<0.001, 0.65±0.09 versus 0.85±0.08) and significantly increased ADC (P<0.01, 1.49±0.17 versus 1.23±0.22).
Conclusion: DTI metrics can be used for preoperative evaluation of the integrity of the CST microstructure.

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We report a case of a 28-year-old woman with hepatocellular adenoma and correlate findings of pathology and magnetic resonance (MR) imaging with gadolinium ethoxybenzyl diethylenetriaminepentaacetic acid (Gd-EOB-DTPA) enhancement. In the hepatobiliary phase, the peripheral region of the tumor that corresponded with proliferating hepatocytes with steatosis showed slight hypointensity compared with the surrounding liver parenchyma, and the central region of the tumor that corresponded with cellular areas showed isointensity.

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We report a case of uterine adenosarcoma demonstrated on magnetic resonance (MR) imaging. A 74-year-old woman with a large uterine mass underwent MR examination before total abdominal hysterectomy. Imaging revealed a markedly enlarged uterus with thin myometrium occupied by a large polypoid mass. The mass contained solid components with low intensity on T₁-weighted images and high intensity on T₂-weighted images compared to the myometrium and areas of small cysts.

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We assessed acute myocardial infarction (AMI) with cardiac rupture in an autopsy using magnetic resonance (MR) imaging in vitro and histological staining. Cardiac MR imaging in vitro generated high resolution images of myocardial thinning, rupture, and epicardial hemorrhage. High signal intensity (SI) on T₁ weighted images (WI) and low SI on T₂WI of the rupture site corresponded with acute myocardial necrosis, edema, and hemorrhage. A rupture site rich in erythrocytes after AMI might affect SI on T₁ and T₂WI in cardiac MR imaging.

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Because it is noninvasive, magnetic resonance microimaging (MRMI) can be used for 3-dimensional measurement of living tissues for cell engineering. Thermal noise in the resonance circuit of the radiofrequency (RF) system of the MRMI cannot become ignored as the signal diminishes in accordance with decreasing sample size, and cooling the RF coil of the receiver circuit can effectively reduce thermal noise. We used a low temperature normal conductor circuit to reduce noise and confirmed improved signal-to-noise ratio for a conventional microimaging system at low B₀ field (0.3T) with low cost.

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We developed a Gd-DTPA (gadolinium(III)-diethylenetriaminepentaacetic acid)-based coating copolymer of hydrophilic and hydrophobic subunits to obtain visibility, hydrophilicity, and durability for passive visualization of catheters used in MR-guided interventions. We then examined a metal-free catheter coated with the polymer in a phantom and in porcine brain tissue ex vivo. Successful visualization of the coated device demonstrated the applicability of the new coating technique for visualizing catheters used in MR-guided interventions.

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We compared diffusion-weighted imaging (DWI) with readout-segmented multi-shot echo-planar imaging (rs-EPI) and single-shot EPI, both using unidirectional motion-probing gradient, in 10 patients for visualization of the anatomical structures in the brainstem. DWI by rs-EPI was significantly better than DWI by single-shot EPI for visualizing the medial longitudinal fasciculus, lateral lemniscus, corticospinal tract, and seventh/eighth cranial nerves and offered significantly less distortion of the brainstem.

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