A multi-dimensional integration (MDI) strategy for MR T2 * mapping

Wave-CAIPI Multiparameter MR Imaging in Neurology

In clinical practice, particularly in neurology assessments, imaging multiparametric MR images with a single-sequence scan is often limited by either insufficient imaging contrast or the constraints of accelerated imaging techniques. A novel single scan 3D imaging method, incorporating Wave-CAIPI and MULTIPLEX technologies and named WAMP, has been developed for rapid and comprehensive parametric imaging in clinical diagnostic applications. Featuring a hybrid design that includes wave encoding, the CAIPIRINHA sampling pattern, dual time of repetition (TR), dual flip angle (FA), multiecho, and optional flow modulation, the WAMP method captures information on RF B1t fields, proton density (PD), T1, susceptibility, and blood flow. This method facilitates the synthesis of multiple qualitative contrast-weighted images and relaxometric parametric maps. A single WAMP scan generates multiple contrast-weighted images and relaxometric parametric maps, including PD-weighted (PDW), T1-weighted (T1W), T2*-weighted (T2W), adjusted T1-weighted (aT1W), susceptibility-weighted imaging (SWI), B1t map, T1 map, T2/R2* map, PD map, and quantitative susceptibility mapping (QSM). Both phantom and in vivo experiments have demonstrated that the proposed method can achieve high image quality and quantification accuracy even at high acceleration factors of 4 and 9. The experiments have confirmed that the rapid single scan method can be effectively applied in clinical neurology, serving as a valuable diagnostic tool for conditions such as pediatric tuberous sclerosis complex (TSC)-related epilepsy, adult Parkinson's disease, and suspected stroke patient. The WAMP method holds substantial potential for advancing multiparametric MR imaging in clinical neurology, promising significant improvements in both diagnostic speed and accuracy.

Complex multi-dimensional integration for T2* and R2* mapping

A dual Multi-Dimensional Integration (dMDI) method was proposed and demonstrated for T2* and R2* mapping. By constructing and jointly using both the original MDI term and an inversed MDI term, T2* and R2* mapping can be performed independently with intrinsic background noise suppression and spike elimination, allowing for high quantitative accuracy and robustness over a wide range of T2*. dMDI was compared to original MDI and curve fitting methods in terms of quantitative specificity, accuracy, reliability and computational efficiency. All methods were tested and compared via simulation and in vivo data. With high signal-to-noise-ratio (SNR), the proposed dMDI method yielded T2*and R2* values similar to curve fitting methods. For low SNR and background noise signals, the dMDI yielded low T2* and R2* values, thus effectively suppressing all background noise. Virtually zero spikes were observed in dMDI T2* and R2* maps in all simulation and imaging results. The dMDI method has the potential to provide improved and reliable T2* and R2* mapping results in routine and SNR-challenging scenarios.

A rapid multi-parametric quantitative MR imaging method to assess Parkinson's disease: a feasibility study

BACKGROUND

MULTIPLEX is a single-scan three-dimensional multi-parametric MRI technique that provides 1 mm isotropic T1-, T2*-, proton density- and susceptibility-weighted images and the corresponding quantitative maps. This study aimed to investigate its feasibility of clinical application in Parkinson's disease (PD).

METHODS

27 PD patients and 23 healthy control (HC) were recruited and underwent a MULTIPLEX scanning. All image reconstruction and processing were automatically performed with in-house C + + programs on the Automatic Differentiation using Expression Template platform. According to the HybraPD atlas consisting of 12 human brain subcortical nuclei, the region-of-interest (ROI) based analysis was conducted to extract quantitative parameters, then identify PD-related abnormalities from the T1, T2* and proton density maps and quantitative susceptibility mapping (QSM), by comparing patients and HCs.

RESULTS

The ROI-based analysis revealed significantly decreased mean T1 values in substantia nigra pars compacta and habenular nuclei, mean T2* value in subthalamic nucleus and increased mean QSM value in subthalamic nucleus in PD patients, compared to HCs (all p values < 0.05 after FDR correction). The receiver operating characteristic analysis showed all these four quantitative parameters significantly contributed to PD diagnosis (all p values < 0.01 after FDR correction). Furthermore, the two quantitative parameters in subthalamic nucleus showed hemicerebral differences in regard to the clinically dominant side among PD patients.

CONCLUSIONS

MULTIPLEX might be feasible for clinical application to assist in PD diagnosis and provide possible pathological information of PD patients' subcortical nucleus and dopaminergic midbrain regions.

Modulation effect of substantia nigra iron deposition and functional connectivity on putamen glucose metabolism in Parkinson's disease

Neurodegeneration of the substantia nigra affects putamen activity in Parkinson's disease (PD), yet in vivo evidence of how the substantia nigra modulates putamen glucose metabolism in humans is missing. We aimed to investigate how substantia nigra modulates the putamen glucose metabolism using a cross-sectional design. Resting-state fMRI, susceptibility-weighted imaging, and [18 F]-fluorodeoxyglucose-PET (FDG-PET) data were acquired. Forty-two PD patients and 25 healthy controls (HCs) were recruited for simultaneous PET/MRI scanning. The main measurements of the current study were R 2 * images representing iron deposition (28 PD and 25 HCs), standardized uptake value ratio (SUVr) images representing FDG-uptake (33 PD and 25 HCs), and resting state functional connectivity maps from resting state fMRI (34 PD and 25 HCs). An interaction term based on the general linear model was used to investigate the joint modulation effect of nigral iron deposition and nigral-putamen functional connectivity on putamen FDG-uptake. Compared with HCs, we found increased iron deposition in the substantia nigra (p = .007), increased FDG-uptake in the putamen (left: PFWE  < 0.001; right: PFWE  < 0.001), and decreased functional connectivity between the substantia nigra and the anterior putamen (left PFWE  < 0.001, right: PFWE  = 0.007). We then identified significant interaction effect of nigral iron deposition and nigral-putamen connectivity on FDG-uptake in the putamen (p = .004). The current study demonstrated joint modulation effect of the substantia nigra iron deposition and nigral-putamen functional connectivity on putamen glucose metabolic distribution, thereby revealing in vivo pathological mechanism of nigrostriatal neurodegeneration of PD.

Augmented T1 -weighted steady state magnetic resonance imaging

T₁ contrasts obtained using short-TR incoherent steady state gradient echo (GRE) methods are generally suboptimal, to which non-T₁ factors in the signals play a major part. In this work, we proposed an augmented T₁ -weighted (aT₁ W) method to extract the signal ratio between routine GRE T₁ W and proton density-weighted signals that effectively removes the non-T₁ effects from the original T₁ W signals, including proton density, T₂ * decay, and coil sensitivity. A recently proposed multidimensional integration (MDI) technique was incorporated in the aT₁ W calculation for better signal-to-noise ratio (SNR) performance. For comparison between aT₁ W and T₁ W results, Monte Carlo noise analysis was performed via simulation and on scanned data, and region-of-interest (ROI) analysis and comparison was performed on the system phantom. For brain scans, the image contrast, noise behavior, and SNR of aT₁ W images were compared with routine GRE and inversion-recovery-based T₁ W images. The proposed aT₁ W method yielded saliently improved T₁ contrasts (potentially > 30% higher contrast-to-noise ratio [CNR]) than routine GRE T₁ W images. Good spatial homogeneity and signal consistency as well as high SNR/CNR were achieved in aT₁ W images using the MDI technique. For contrast-enhanced (CE) imaging, aT₁ W offered stronger post-CE contrast and better boundary delineation than T₁ MPRAGE images while using a shorter scan time.

MULTI-parametric MR imaging with fLEXible design (MULTIPLEX)

PURPOSE

To introduce a gradient echo (GRE) -based method, namely MULTIPLEX, for single-scan 3D multi-parametric MRI with high resolution, signal-to-noise ratio (SNR), accuracy, efficiency, and acquisition flexibility.

THEORY

With a comprehensive design with dual-repetition time (TR), dual flip angle (FA), multi-echo, and optional flow modulation features, the MULTIPLEX signals contain information on radiofrequency (RF) B_1t fields, proton density, T₁ , susceptibility and blood flows, facilitating multiple qualitative images and parametric maps.

METHODS

MULTIPLEX was evaluated on system phantom and human brains, via visual inspection for image contrasts and quality or quantitative evaluation via simulation, phantom scans and literature comparison. Region-of-interest (ROI) analysis was performed on parametric maps of the system phantom and brain scans, extracting the mean and SD of the T₁ , T2∗ , proton density (PD), and/or quantitative susceptibility mapping (QSM) values for comparison with reference values or literature.

RESULTS

One MULTIPLEX scan offers multiple sets of images, including but not limited to: composited PDW/T₁ W/ T2∗ W, aT₁ W, SWI, MRA (optional), B_1t map, T₁ map, T2∗ / R2∗ maps, PD map, and QSM. The quantitative error of phantom T₁ , T2∗ and PD mapping were <5%, and those in brain scans were in good agreement with literature. MULTIPLEX scan times for high resolution (0.68 × 0.68 × 2 mm³ ) whole brain coverage were about 7.5 min, while processing times were <1 min. With flow modulation, additional MRA images can be obtained without affecting the quality or accuracy of other images.

CONCLUSION

The proposed MUTLIPLEX method possesses great potential for multi-parametric MR imaging.