Keywords: Microstructure, Microstructure, Signal Representations, Prostate

Motivation: Clinical diffusion MRI for prostate cancer diagnosis has limited sensitivity and specificity to heterogenous microstructural changes.

Goal(s): Quantify time-dependent diffusion and diffusional variance at a high spatial resolution in human prostate in vivo.

Approach: The diffusion encoding waveforms were tailored to probe micro-anisotropy and diffusion time effects at high b-values. Ultra-strong gradients and spiral readout enabled high-resolution  and high image fidelity at a high SNR.

Results: Significant time-dependent diffusion was observed in all diffusion parameters in three volunteers, including prostate cancer patients.

Impact: The proposed methodology enables evaluation of microscopic anisotropy and time-dependent diffusion in the prostate and provides insights into how dMRI should be interpreted at low and high b-values. The produced diffusion parameters may serve as biomarker candidates in future studies.

Keywords: Breast, Breast, Diffusion, RSI

Motivation: Diffusion weighted imaging (DW-MRI) holds great potential in improving specificity of findings detected on contrast enhanced breast MRI. A breast-specific Restriction spectrum imaging (BS-RSI) has been developed and proved to be able to discriminate cancers from benign lesions and healthy breast tissue.

Goal(s): To evaluate BS-RSI’s performance in differentiating malignant from healthy fibroglandular tissue in a breast cancer screening dataset (BCS).

Approach: We prospectively scanned 14 BCS patients with high-resolution multishell DWI added to standard BCS clinical protocol.

Results: The BS-RSI model was able to discriminate healthy tissue from cancers in all C-compartments.

Impact: Differences were observed between healthy tissue and malignant lesions in all C-compartments (p<0.01). ADC values were also significantly different in cancers than in healthy issue (p=0.044).

Keywords: IVIM, Liver, liver cirrhosis, perfusion

Motivation: Pancreatic perfusion disturbances is found in cirrhotic patients with portal hypertension, which is correlated with reduced insulin secretion. Intravoxel incoherent motion (IVIM) can noninvasively reflect tissue microcapillary perfusion.

Goal(s): To assess the characteristics of pancreatic perfusion in normal pancreas vs. cirrhotic patients using IVIM.

Approach: 67 cirrhotic patients and 33 healthy subjects underwent IVIM on a 3.0 T MRI scanner.

Results: The f value of pancreas in cirrhotic was lower than that in normal group (p = 0.01). In cirrhotic group, the f value of pancreas decreased with the increase of the Child-Pugh classification (R = -0.49, p = 0.00).

Impact: IVIM-derived perfusion-related parameter (f value) could be helpful to evaluate pancreatic perfusion in liver cirrhosis. Pancreatic perfusion decreased is present in liver cirrhosis, and pancreatic perfusion tends to decrease with the increasing severity of hepatic function.

Keywords: IVIM, Velocity & Flow, Liver, Perfusion, Quantitative Imaging

Motivation: Food ingestion is known to increase blood flow in the liver. However, detection of prandial effects using conventional quantitative intravoxel incoherent motion (IVIM) methods is confounded by large measurement variability of the perfusion-related IVIM parameters.

Goal(s): Detect prandial-induced changes in IVIM estimates in the liver.

Approach: 2D (b-value and first-order motion moment (M₁)) noise-optimized IVIM acquisitions were acquired pre- and postprandial. IVIM estimates were obtained using a recently proposed advanced fitting technique. Pre- vs postprandial IVIM estimates were compared.

Results: The optimized IVIM methods detected prandial-induced changes in the blood velocity standard deviation (mean relative change=9.4±7.8%; preprandial coefficient of variation=5.6%).

Impact: Quantitative IVIM is capable of detecting prandial-induced changes in blood perfusion in the liver. Liver IVIM data may need to be acquired in a fasting state, and evaluating prandial effects may provide insight into various diseases’ pathophysiological changes.

Keywords: Microstructure, Liver

Motivation: The potential of characterizing cellular tissue microstructures using recently developed time-dependent diffusion MRI has been examined.

Goal(s): However, its value in imaging liver fibrosis to cirrhosis remains unknown.

Approach: In this study, we conducted a preclinical investigation using a dietondiethylnitrosamine (DEN)-induced rat liver fibrosis model with temporal diffusion spectroscopy (TDS) MRI

Results: Our findings revealed that the diameter, intracellular volume fraction (V_in), and cellularity were associated with varying degrees of liver fibrosis. Moreover, the diameter and V_in demonstrated better discrimination ability in the model. Overall, these prognostic indicators exhibit significant potential for clinical application.

Impact: This research highlighted the promising applications of temporal diffusion spectroscopy MRI in evaluating liver fibrosis. Our results indicated innovative noninvasive indicators for liver fibrosis, so as to early identify those who need to be referred to clinics for further assessment.

Keywords: Diffusion Modeling, Quantitative Imaging, Signal Modeling, Inversion Recovery, Data Analysis, Contrast Mechanisms, Cancer

Motivation: The apparent diffusion coefficient (ADC) of prostate tissue is generally higher than that of prostate cancer. We hypothesized that the presence of prostatic fluid is partly responsible for the higher ADC. 

Goal(s): To elucidate the value of this hypothesis with diffusion-T₁-relaxation experiments.

Approach: Diffusion-weighted data of ten healthy participants’ prostates were sampled with a range of IR times and fitted to a two-compartment model (tissue & fluid). 

Results: The ADC(TI) dependency was characteristic of the two-compartment model. ADC(TI) increased with TI from 0 to roughly 1,200 ms, then flipped to smaller ADC values and then approached an asymptotic value at large TI.

Impact: This study contributes to a better understanding of prostate DWI contrast. The observed ADC(TI) dependence may be exploited for improved DWI-based prostate cancer diagnostics.

Keywords: Diffusion Modeling, Microstructure, Sciatic nerve, axon radius, Multiple Sclerosis

Motivation: The stick (zero-radius cylinder), a standard diffusion MRI model for the intra-axonal brain white matter signal, may not be suitable in the peripheral nervous system (PNS), due to co-existence of small and large axons.

Goal(s): To test the feasibility of replacing the stick model with a two-axon population (TAP) approach, accounting for large axons, in the PNS.

Approach: We compared TAP versus standard stick modelling in simulations, and derived TAP metrics in the sciatic nerve in vivo.

Results: TAP enables more accurate parameter fitting than stick modelling, and is shown to be feasible in vivo in healthy controls and multiple sclerosis patients.

Impact: We propose two-axon population (TAP) diffusion-weighted MRI, a method tailored for imaging of the peripheral nervous system, characterised by co-existence of small and large axons. TAP may enable more accurate microstructural imaging than standard approaches, providing non-invasive markers of neurophysiology.

Keywords: IVIM, Cardiovascular

Motivation: Intravoxel incoherent motion (IVIM) imaging can provide information about cardiac microstructure and microvascular perfusion from a single examination. Current spin-echo based approaches for cardiac IVIM suffer from low perfusion sensitivity.

Goal(s): We implemented a stimulated-echo (STEAM)-based method for cardiac IVIM and diffusion tensor imaging to enable accurate cardiac diffusion and perfusion imaging in vivo in the human heart.

Approach: We introduced a novel IVIM-STEAM sequence incorporating phase cycling to obtain true b=0 s/mm² images. 

Results: We tested the feasibility of our approach in 9 healthy subjects and obtained homogeneous perfusion and diffusion tensor maps, with values in the range described in the literature.

Impact: Phase-cycled IVIM-STEAM provides good quality images that enable reliable fitting of cardiac diffusion tensor and perfusion parameters in healthy subjects. This approach may identify areas of microstructural aberration and perfusion abnormalities in patients with cardiovascular disease without exogenous contrast agents.

Keywords: Tractography, Diffusion Tensor Imaging

Motivation: In the skeletal muscles, the effects of varying diffusion times have rarely been investigated, and to what extent they are affected is unclear. 

Goal(s): This study aimed to determine the effect of diffusion time on skeletal muscle delineation and anisotropy. 

Approach: Tensor analysis and tractography measurements were performed on the hind legs of mice to investigate the relationship between diffusion time and myofiber delineation and anisotropy in skeletal muscles.

Results: Longer diffusion times allowed us to assess diffusion movements within muscle fibers and capture the precise organization of the skeletal muscles.

Impact: The effect of varying diffusion times on skeletal muscle myofibers was clarified. The results suggested that this method could be applied to human skeletal muscles for the examination of intramuscular tissues.

Keywords: Microstructure, Quantitative Imaging

Motivation: Conventional MRI falls short in detecting specific imaging markers for an intraductal component(ductal carcinoma in situ) in invasive breast cancer (IBC-IC), thus affecting breast-conserving surgery. Advanced MRI techniques can help in preoperative evaluations.

Goal(s): We evaluated the efficacy of td-dMRI for preoperatively identifying IBC-IC for surgical planning.

Approach: We used td-dMRI to examine microstructural mapping in IBC patients  by IMPULSED model, focusing on the parameters D_ex, d, and v_in to differentiate IBC-IC from IBC.

Results: We revealed that elevated d and D_ex and reduced v_in are distinct microstructural markers of IBC-IC, which might facilitate surgical planning for IBC-IC patients.

Impact: Parameters derived from td-dMRI have the potential to act as imaging biomarkers for distinguishing IBC-IC, thereby enhancing the precision of breast-conserving surgery planning.