Purpose: To develop a fast and precise method for searching rectangular regions in brain tumor images.

Methods: The authors propose a new method for searching rectangular tumor regions in brain MR images. The proposed method consisted of a segmentation network and a fast search method with a user-controllable search metric. As the segmentation network, the U-Net whose encoder was replaced by the EfficientNet was used. In the fast search method, summed-area tables were used for accelerating sums of voxels in rectangular regions. Use of the summed-area tables enabled exhaustive search of the 3D offset (3D full search). The search metric was designed for giving priority to nearly isotropic rectangles over undesirable thin rectangles, and assigning better values for higher tumor fractions even if they exceeded target tumor fractions. The proposed computation and metric were compared with those used in a conventional method using the Brain Tumor Image Segmentation dataset.

Results: When the 3D full search was used, the proposed computation (8 seconds) was 100–500 times faster than the conventional computation (11–40 minutes). When the user-controllable parts of the search metrics were changed variously, the tumor fractions of the proposed metric were higher than those of the conventional metric. In addition, the conventional metric preferred undesirable thin rectangles whereas the proposed metric preferred nearly isotropic rectangles.

Conclusion: The proposed method is promising for implementing fast and precise search of rectangular tumor regions, which is useful for brain tumor diagnosis using MRI systems. The proposed computation reduced processing times of the 3D full search, and the proposed metric improved the quality of the assigned rectangular tumor regions.

We have developed a practical method to determine the optimal number of signal averages (NSAs) for acquiring a spectrum in the human brain and determined the optimal number of NSA at 7-Tesla. We performed 50 sequential data acquisitions with an NSA of 2 in healthy volunteers and then generated spectra with NSAs ranging from 2 to 100. After identifying the metabolites with Cramér–Rao lower bounds (CRLB) ≤ 15% in the NSA 100 spectrum, we examined the CRLB values, creatine+phosphocreatine (Cr + PCr) ratios and agreement of Cr + PCr ratios. Eight metabolites and 5 metabolite pairs spectrum showed CRLB values ≤ 15% when the NSA was 40 or higher. Additionally, the Cr + PCr ratios at NSA 40 closely matched those at NSA 100. By analyzing the CRLB values of metabolites in varying NSAs spectra generated from sequential data, we determined the optimal NSA needed to accurately measure the spectrum within a reasonable acquisition time.

Purpose: To study the potential advantages of phosphorus magnetic resonance spectroscopy (³¹P-MRS) in differentiating advanced from mild fibrosis in non-alcoholic fatty liver disease (NAFLD) and early diagnosis at high field strength MR (9.4 Tesla).

Methods: Fibrosis of normal and carbon tetrachloride (CCl₄)-treated male rats was staged into: none (F0), perisinusoidal or periportal (F1), perisinusoidal and portal/periportal (F2), bridging fibrosis (F3) and cirrhosis (F4) by Sirius Red staining. The degree of steatosis and inflammatory activity were also graded based on Hematoxylin and Eosin staining. Rats were divided into different groups by different stages of fibrosis (F0, F1–2, F3–4) and laboratory blood tests were performed to verify the degree of liver injury. ³¹P-MRS was performed at 9.4T MR to obtain signal peaks of different phosphorus metabolites and the changes of the ratios between the peaks were observed.

Results: At 9.4 T, phosphoethanolamine (PE), phosphocholine (PC) and glycerophosphorylethanolamine (GPE), glycerophosphorylcholine (GPC) could be separated respectively from the peaks of phosphomonoesters (PME) and phosphodiesters (PDE), meanwhile nicotinamide adenine dinucleotide phosphate (NADPH) and uridine diphosphate glucose (UDPG) showed up as well. The marker of cell membrane metabolism, in F1–2, PME/PDE (P < 0.001), PC/GPE (P < 0.01), PC/GPC (P < 0.05) and PC/(PME + PDE) (P < 0.05) decreased while GPE/(PME + PDE) (P < 0.05) and GPC/(PME + PDE) (P < 0.05) increased significantly. In F3–4, there was a recovery trend of most ratios, especially for PC/(PME + PDE) (P < 0.05). As for the main ratio related to energy metabolism, β-ATP/P_total (P < 0.05) decreased in the early stage of the disease (F1–2) and this decline was maintained in advanced stage (F3–4). NADPH/P_total (P < 0.01) and β-ATP/Pi (inorganic phosphate) (P < 0.05) ratio was lower in F3–4 comparing with F0.

Conclusion: ³¹P-MRS can generally stage the liver fibrosis by comparing the ratios of the phosphorus metabolites resonance peaks at 9.4 T and more importantly it can be used for early diagnosis.

Two-pulse phase-modulated (TPPM) ¹H-decoupling pulse sequence repeats a pair of 180^o RF pulses while changing the signs of the RF phase modulation angle and has been widely used for the ¹³C NMR of organic solids. TPPM was introduced into the ¹³C MRS pulse sequence on a clinical 3T MR scanner, and the ¹H-decoupling performance was compared with conventional ¹H-decoupling schemes using aqueous solutions containing glucose and oyster glycogen. The ¹³C C1-glucose peaks were ¹H-decoupled using TPPM with B₂ = 500 Hz, and the optimal RF phase modulation angle was up to 30^o. Cycling sidebands were not observed when TPPM was used but were observed when WALTZ-16 was used. The ¹³C C1-glycogen peak was ¹H-decoupled even with reducing TPPM duration to 8 ms, which reduced simulated specific absorption rate (SAR) to 39%. In conclusion, the TPPM ¹H decoupling is applicable to clinical MR scanners, and the low-SAR sequence may be more valuable at 7T.

Purpose: To develop a new method to generate synthetic MR spectroscopic imaging (MRSI) data for training machine learning models.

Methods: This study targeted routine MRI examination protocols with single voxel spectroscopy (SVS). A novel model derived from pix2pix generative adversarial networks was proposed to generate synthetic MRSI data using MRI and SVS data as inputs. T1- and T2-weighted, SVS, and reference MRSI data were acquired from healthy brains with clinically available sequences. The proposed model was trained to generate synthetic MRSI data. Quantitative evaluation involved the calculation of the mean squared error (MSE) against the reference and metabolite ratio value. The effect of the location of and the number of the SVS data on the quality of the synthetic MRSI data was investigated using the MSE.

Results: The synthetic MRSI data generated from the proposed model were visually closer to the reference. The 95% confidence interval (CI) of the metabolite ratio value of synthetic MRSI data overlapped with the reference for seven of eight metabolite ratios. The MSEs tended to be lower in the same location than in different locations. The MSEs among groups of numbers of SVS data were not significantly different.

Conclusion: A new method was developed to generate MRSI data by integrating MRI and SVS data. Our method can potentially increase the volume of MRSI data training for other machine learning models by adding SVS acquisition to routine MRI examinations.

Purpose: Chronic obstructive pulmonary disease (COPD) is a complex multisystem disease associated with comorbidities outside the lungs. The aim of this study was to measure changes in metrics of pulmonary gas exchange function and brain tissue metabolism in a mouse model of COPD using hyperpolarized ¹²⁹Xe (HP ¹²⁹Xe) MRI/MR spectroscopy (MRS) and investigate the relationship between the metrics of lung and brain.

Methods: COPD phenotypes were induced in 15 mice by 6-week administration of cigarette smoke extract (CSE) and lipopolysaccharide (LPS). A separate negative control (NC) group was formed of 6 mice administered with saline for 6 weeks. After these 6-week administrations, the pulmonary gas exchange function parameter f_D (%) and the rate constant, α (s⁻¹), which are composed of the cerebral blood flow F_i and the longitudinal relaxation rate 1/T_1i in brain tissue, were evaluated by HP ¹²⁹Xe MRI/MRS.

Results: The f_D of CSE-LPS mice was significantly lower than that of NC mice, which was in parallel with an increase in bronchial wall thickness. The α in the CSE-LPS mice decreased with the decrease of f_D in contrast to the trend in the NC mice. To further elucidate the opposed trend, the contribution of T_1i was separately determined by measuring F_i. The T_1i in the CSE-LPS mice was found to correlate negatively with f_D as opposed to the positive trend in the NC mice. The opposite trend in T_1i between CSE-LPS and NC mice suggests hypoxia in the brain, which is induced by the impaired oxygen uptake as indicated by the reduced f_D.

Conclusion: This study demonstrates the feasibility of using HP ¹²⁹Xe MRI/MRS to study pathological mechanisms of brain dysfunction in comorbidities with COPD.

MR spectroscopy (MRS) is a unique and useful method for noninvasively evaluating biochemical metabolism in human organs and tissues, but its clinical dissemination has been slow and often limited to specialized institutions or hospitals with experts in MRS technology. The number of 3-T clinical MR scanners is now increasing, representing a major opportunity to promote the use of clinical MRS. In this review, we summarize the theoretical background and basic knowledge required to understand the results obtained with MRS and introduce the general consensus on the clinical utility of proton MRS in routine clinical practice. In addition, we present updates to the consensus guidelines on proton MRS published by the members of a working committee of the Japan Society of Magnetic Resonance in Medicine in 2013. Recent research into multinuclear MRS equipped in clinical MR scanners is explained with an eye toward future development. This article seeks to provide an overview of the current status of clinical MRS and to promote the understanding of when it can be useful. In the coming years, MRS-mediated biochemical evaluation is expected to become available for even routine clinical practice.