Motion and temporal B0-shift corrections for QSM and mapping using dual-echo spiral navigators and conjugate-phase reconstruction.

BackgroundCerebral microbleeds (CMBs) are small hypointense round lesions that indicate leakage of blood products from cerebral vessels damaged by β‐amyloid‐40 (Aβ) and typically are detected by T2*‐weighted and susceptibility weighted imaging (SWI) on MRI. They are indicators of cerebral small vessel diseases, especially cerebral amyloid angiopathy (CAA), affecting cortical small arteries. Quantitative susceptibility mapping (QSM) is an advanced MRI imaging technique used to quantify the magnetic susceptibility of tissues in the human body. In this study, we utilized the QSM technique to analyze venous structures at ultra‐high resolution in a cohort of patients with AD and age‐matched control subjects using 7T MRI. Our aim is to evaluate the feasibility of using ultra‐high resolution QSM at 7T MRI to find a link between small veins and CMBs in individuals with AD.MethodIn‐vivo human imaging was performed using a 7T MRI scanner and were analyzed by two neuroradiologists. CMBs were defined as hyperintense, round lesions in the QSM images. For verification, their appearance was matched on the SWI images, where CMBs are hypointense and associated with. CMBs with an immediate adjacent to a vein were assessed in the QSM images. They were defined as CMBs with small veins connection.ResultThis high‐resolution 7T neuroimaging study investigated whether a spatial relationship between small veins and CMBs could be detected in a cohort of AD patients. QSM enabled depiction of cerebral CMBs with a direct connection to a vein and their localization. Our data support the notion that CMBs relate anatomically to veins. Understanding the role of vein pathology in CAA and its role in neurodegenerative pathologies might open novel insights in the pathophysiology of AD.ConclusionA key strength of our study lies in the utilization of high‐resolution QSM at 7T MRI. High‐resolution MRI enhances the visibility of small structures, and when maintained at the same resolution, imaging at a higher field MRI increases the signal‐to‐noise ratio. QSM elevates CMB detection sensitivity while facilitating precise visualization of the brain's venous vasculature. Notably, the postprocessing algorithm ensures a high level of specificity for venous blood susceptibilities, minimizing the likelihood of measuring arterioles or slow‐flow small arteries.

Quantitative susceptibility mapping (QSM) is a magnetic resonance imaging (MRI) technique that can measure the magnetic susceptibility of tissues, which can reflect their iron content. QSM has been used to detect iron accumulation in cortical and subcortical brain regions. However, its application in subcortical regions such as the basal ganglia, particularly the putamen, is rare in patients with amyotrophic lateral sclerosis (ALS). We present the case of a 40-year-old male patient with ALS who underwent an MRI for QSM. We compared his QSM images with those of a control subject and performed a quantitative analysis of the magnetic susceptibility values in the putamen regions. We also reviewed the literature on previous QSM studies in ALS and summarized their methods and findings. Our QSM analysis revealed increased magnetic susceptibility values in the bilateral putamen of the ALS patient compared to controls, indicating iron overload. This finding is consistent with previous studies reporting iron dysregulation in subcortical nuclei in ALS. We also discussed the QSM processing techniques used in our study and in the literature, highlighting their advantages and limitations. This case report demonstrates the potential of QSM as a sensitive MRI biomarker for evaluating iron levels in subcortical regions of ALS patients. QSM can provide quantitative information on iron deposition patterns in both motor and extra-motor areas of ALS patients, which may help understand the pathophysiology of ALS and monitor disease progression. Further studies with larger samples are needed to validate these results and explore the clinical implications of QSM in ALS.

BackgroundRespiratory motion in PET/CT leads to well-known image degrading effects commonly compensated using elastic motion correction approaches. Gate-to-gate motion correction techniques are promising tools for improving clinical PET data but suffer from relatively long reconstruction times. In this study, the performance of a fast elastic motion compensation approach based on motion deblurring (DEB-MC) was evaluated on patient and phantom data and compared to an EM-based fully 3D gate-to-gate motion correction method (G2G-MC) which was considered the gold standard.MethodsTwenty-eight patients were included in this study with suspected or confirmed malignancies in the thorax or abdomen. All patients underwent whole-body [18F]FDG PET/CT examinations applying hardware-based respiratory gating. In addition, a dynamic anthropomorphic thorax phantom was studied with PET/CT simulating tumour motion under controlled but realistic conditions. PET signal recovery values were calculated from phantom scans by comparing lesion activities after motion correction to static ground truth data. Differences in standardized uptake values (SUV) and metabolic volume (MV) between both reconstruction methods as well as between motion-corrected (MC) and non motion-corrected (NOMC) results were statistically analyzed using a Wilcoxon signed-rank test.ResultsPhantom data analysis showed high lesion recovery values of 91% (2 cm motion) and 98% (1 cm) for G2G-MC and 83% (2 cm) and 90% (1 cm) for DEB-MC. The statistical analysis of patient data found significant differences between NOMC and MC reconstructions for SUV max, SUV mean, MV, and contrast-to-noise ratio (CNR) for both reconstruction algorithms. Furthermore, both methods showed similar increases of 11–12% in SUV max and SUV mean after MC. The statistical analysis of the MC/NOMC ratio found no significant differences between the methods.ConclusionBoth motion correction techniques deliver comparable improvements of SUV max, SUV mean, and CNR after MC on clinical and phantom data. The fast elastic motion compensation technique DEB-MC may thereby be a valuable alternative to state-of-the art motion correction techniques.

Voxel-based morphometry (VBM) is widely used to quantify the progression of Alzheimer's disease (AD), but improvement is still needed for accurate early diagnosis. We evaluated the feasibility of a novel diagnosis index for early diagnosis of AD based on quantitative susceptibility mapping (QSM) and VBM. Thirty-seven patients with AD, 24 patients with mild cognitive impairment (MCI) due to AD, and 36 cognitively normal (NC) subjects from four centers were included. A hybrid sequence was performed by using 3-T MRI with a 3D multi-echo GRE sequence to obtain both a T1-weighted image for VBM and phase images for QSM. The index was calculated from specific voxels in QSM and VBM images by using a linear support vector machine. The method of voxel extraction was optimized to maximize diagnostic accuracy, and the optimized index was compared with the conventional VBM-based index using receiver operating characteristic analysis. The index was optimal when voxels were extracted as increased susceptibility (AD > NC) in the parietal lobe and decreased gray matter volume (AD < NC) in the limbic system. The optimized proposed index showed excellent performance for discrimination between AD and NC (AUC = 0.94, p = 1.1 × 10-10) and good performance for MCI and NC (AUC = 0.87, p = 1.8 × 10-6), but poor performance for AD and MCI (AUC = 0.68, p = 0.018). Compared with the conventional index, AUCs were improved for all cases, especially for MCI and NC (p < 0.05). In this preliminary study, the proposed index based on QSM and VBM improved the diagnostic performance between MCI and NC groups compared with the VBM-based index. • We developed a novel diagnostic index for Alzheimer's disease based on quantitative susceptibility mapping (QSM) and voxel-based morphometry (VBM). • QSM and VBM images can be acquired simultaneously in a single sequence with little increasing scan time. • In this preliminary study, the proposed diagnostic index improved the discriminative performance between mild cognitive impairment and normal control groups compared with the conventional VBM-based index.

ObjectiveIn dynamic susceptibility contrast MRI (DSC-MRI), an arterial input function (AIF) is required to quantify perfusion. However, estimation of the concentration of contrast agent (CA) from magnitude MRI signal data is challenging. A reasonable alternative would be to quantify CA concentration using quantitative susceptibility mapping (QSM), as the CA alters the magnetic susceptibility in proportion to its concentration.Material and methodsAIFs with reasonable appearance, selected on the basis of conventional criteria related to timing, shape, and peak concentration, were registered from both ΔR2* and QSM images and mutually compared by visual inspection. Both ΔR2*- and QSM-based AIFs were used for perfusion calculations based on tissue concentration data from ΔR2*as well as QSM images.ResultsAIFs based on ΔR2* and QSM data showed very similar shapes and the estimated cerebral blood flow values and mean transit times were similar. Analysis of corresponding ΔR2* versus QSM-based concentration estimates yielded a transverse relaxivity estimate of 89 s−1 mM−1, for voxels identified as useful AIF candidate in ΔR2* images according to the conventional criteria.DiscussionInterestingly, arterial concentration time curves based on ΔR2* versus QSM data, for a standard DSC-MRI experiment, were generally very similar in shape, and the relaxivity obtained in voxels representing blood was similar to tissue relaxivity obtained in previous studies.

Quantitative susceptibility mapping has been proposed to assess intraplaque hemorrhage (IPH) in the carotid artery. The purpose of this study was to compare the diagnostic accuracy of preoperative quantitative susceptibility mapping with that of the conventional T1-weighed 3D-FSE sequence for detecting IPH in cervical ICA stenosis in patients undergoing carotid endarterectomy by using histology as the reference standard. Carotid T1-weighted 3D-FSE and QSM images were obtained from 16 patients with cervical ICA stenosis before carotid endarterectomy. Relative signal intensity and susceptibility of the ICA were measured on 3 axial images, including the location of most severe stenosis on T1-weighted 3D-FSE and quantitative susceptibility mapping images, respectively. Three transverse sections of carotid plaques excised by carotid endarterectomy, which corresponded with images on MR imaging, were stained with H&E, antibody against glycophorin A, and Prussian blue, and the relative area of histologic IPH was calculated. The correlation coefficient was significantly greater between susceptibility and relative area-histologic IPH (ρ = 0.691) than between relative signal intensity and relative area-histologic IPH (ρ = 0.413; P = .0259). The areas under the receiver operating characteristic curves for detecting histologic sections consisting primarily of IPH (relative area-histologic IPH > 40.7%) tended to be greater for susceptibility (0.964) than for T1WI FSE-relative signal intensity (0.811). Marginal homogeneity was observed between susceptibility and histologic sections consisting primarily of IPH (P = .0412), but not between T1-weighted FSE-relative signal intensity and histologic sections consisting primarily of IPH (P = .1824). Pre-carotid endarterectomy quantitative susceptibility mapping detects histologic IPH in cervical ICA stenosis more accurately than preoperative T1-weighted 3D-FSE imaging.

Chronic drug doping has a great influence on the functional and morphological properties of brain tissues. However, the underlying mechanism related to these variations remains unclear. Since there are evidences showing that iron concentration affects the synthesis of dopamine and monoamine metabolism, in the present work, we propose to use quantitative susceptibility mapping (QSM) to investigate the iron distribution in the brain tissues. To achieve this, 9 heroin users (HUs) and 2 controls (CLs) were recruited for MRI scanning. QSM images were obtained firstly with STI-suite and then registered and segmented with a QSM atlas and parcellation maps. The results demonstrated that, the HUs experienced higher iron accumulation in putamen, globus pallidus, caudate nucleus and thalamus than CLs. Our findings showed that there is a link between the morphological changes and the iron concentration variations in the brain of Hus. This would be helpful for understanding the underlying mechanism by which drug addiction affects the brain and providing the guidance for effective treatment strategies.

Myotonic dystrophy type 1 is a dominantly inherited disorder, affecting musculoskeletal and central nervous systems and mainly characterized by progressive muscular atrophy and multisystemic damages including cardiac, respiratory and sleep dysfunctions. Neuroimaging studies conducted in myotonic dystrophy type 1 patients have documented widespread cerebral alterations encompassing structural, microstructural, functional and metabolic aspects of the brain, while comparatively few studies have investigated the role of iron concentration in the pathophysiology of central nervous system impairment. We report here the use of quantitative susceptibility (χ) mapping to explore iron content of both cortical and subcortical structures in myotonic dystrophy type 1 patients and to assess its possible clinical relevance, combining imaging and clinical data. Thirty-four myotonic dystrophy type 1 participants (20 females, 46.8 ± 12.0 years old) and 35 age- and sex- matched healthy controls (20 females, 50.5 ± 17.3 years old) were included in the study. All participants underwent MRI examinations in the same 3-Tesla scanner. The MRI protocol included 3D morphological T1-weighted magnetization prepared rapid gradient echo and T2*weighted multi-echo gradient echo for quantitative susceptibility mapping reconstruction. Cortical and subcortical structures were automatically segmented, and a volume of interest–based analysis was performed; χ distributions were compared between the two groups and myotonic dystrophy type 1 χ values were correlated with clinical and laboratory data. In the myotonic dystrophy type 1 group, a significant increase of χ was found in almost all cortical gyri, as a non-specific sign of neurodegeneration. Among subcortical structures, χ was significantly higher in myotonic dystrophy type 1 group in both thalamus (ventral and pulvinar nuclei) and brainstem (pons and medulla), compared to healthy controls. Additionally, correlation analysis showed some links between χ in subcortical structures and clinical signs, suggesting greater iron concentration with deterioration of clinical conditions. Thalamic χ values were associated with cardiological parameters and disability scores and, as with brainstem χ, they were also positively correlated with the number of central apnoeas; finally, thalamic and brainstem χ were negatively correlated with the age of onset. This study showed a correlation between autonomic dysfunction related to certain subcortical structures and their χ; higher values of χ correlated with greater functional impairment, suggesting iron accumulation detected by the quantitative susceptibility mapping technique is a possible biomarker of disease progression.

Dynamic changes in cerebrovascular reactivity after acetazolamide administration vary markedly among patients with major cerebral arterial steno-occlusive disease. MR quantitative susceptibility mapping can dynamically quantify the cerebral magnetic susceptibility. The purpose of this study was to determine whether dynamic changes in susceptibility after administration of acetazolamide on 7T quantitative susceptibility mapping are associated with pre-existing states of CBV and the cerebral metabolic rate of oxygen in the cerebral hemispheres with major cerebral arterial steno-occlusive disease. Sixty-five patients underwent 7T MR imaging at baseline and at 5, 10, 15, and 20 minutes after acetazolamide administration. Differences between the susceptibility of venous structures and surrounding brain tissue were calculated in the quantitative susceptibility mapping images. Susceptibility differences at 5, 10, 15, and 20 minutes after acetazolamide administration relative to baseline were calculated in 97 cerebral hemispheres with major cerebral arterial steno-occlusive disease. CBV and the cerebral metabolic rate of oxygen were also calculated using 15O-gas PET in the resting state. Dynamic changes of susceptibility after acetazolamide administration were classified into 3 patterns: abnormally increasing 5 or 10 minutes after acetazolamide administration; abnormally decreasing within 20 minutes after acetazolamide administration; and remaining unchanged after acetazolamide administration. CBV was significantly greater in the first pattern than in the latter 2. The cerebral metabolic rate of oxygen differed significantly in descending order from the first to middle to last pattern. Dynamic changes of susceptibility after acetazolamide administration on 7T MR quantitative susceptibility mapping are associated with pre-existing states of CBV and the cerebral metabolic rate of oxygen in major cerebral arterial steno-occlusive disease.

Advances in PET technology have led to improved resolution capability in modern PET scanners, andhence the impact of motion has become increasingly significant in order to produce high resolutionPET images. This thesis aims to advance the utility of motion correction in combined PET and MR byimproving the capabilities of motion correction, and by easing the effort required in order to applythem. In particular, PET-based data-driven motion tracking methods, which are able to track motionwithout requiring additional hardware, are investigated and applied to the head. First, existing techniques for motion correction, especially in the context of PET/MR, are reviewedand a general framework for PET motion correction is presented. The framework provides a top-levelperspective on PET motion correction, simplifying the process of comparing and contrasting variousmotion correction techniques. Next, the implementation of a patient-based orientation system withinthe open-source PET reconstruction packages the Software for Tomographic Image Reconstruction(STIR) and the Synergistic Image Reconstruction Software (SIRF) is described. Additionally, animplementation of the general PET motion correction framework platform is introduced. To investigate current technological limitations in combined PET and MR motion correction, theefficacy of a commercial PET/MR motion correction product, Brain COMPASS (herein just COMPASSfor brevity), was assessed. An experiment introduced a methodology for measuring motion blur invivo and uses this to measure reduction in motion blur after applying COMPASS. N=10 subjects worea head-mounted apparatus with fiducial markers affixed. COMPASS reduced blur in the directionof motion, measured by the principal component of the full-width at half-maximum (FWHM) ofthe source point-spread-function (PSF) distribution, only when the motion was sufficient to causethat blur to exceed 1.9 mm. However, blur across all directions almost always increased (mean=0.3mm) when COMPASS was used. Results suggested that any error in estimating the patient posewas low and was not the cause of the blur. Increases in overall blur were therefore suspected to becaused by interpolation when resampling transformed reconstructions. A second experiment measuredneocortical standardised uptake value ratio (SUVr) in an 18F-Florbetaben (18F-FBB) study of N=42young, healthy, asymptomatic volunteers with high polygenetic risk of developing Alzheimer’s Disease.No significant changes in neocortical SUVr were observed. This cohort exhibited low motion, andthe neocortex is a large region-of-interest, so is less sensitive to motion corruption than other cohorts.Hence, it was concluded that COMPASS did not aid this investigation, but also does not have adiscernible negative impact despite low motion. During the COMPASS investigation, MR acquisitions were the time-limiting factor of the session,meaning that the MR acquisitions introduced for PET motion correction increased the overall sessiontime. Because MR is not always available for motion tracking, alternative PET-alone motion correctiontechniques were investigated. Several data-driven tracking techniques are available; however, it is notclear which are most appropriate. A phantom investigation was conducted on a Biograph mCT Flowto determine which data-driven head motion tracking techniques were most appropriate. Of the fourmethodologies investigated principal component analysis (PCA) was found to be the most promisingtechnique for PET data-driven motion tracking of head motion. The PET-alone motion correction technique outlined above had two key limitations. Firstly, theyprovide frame-based motion correction with low temporal resolution. However, the type of motionseen in the COMPASS investigation were continuous “drooping” of the head, is not modelled in adiscrete, frame-based scheme. Secondly, the PET reconstructions without attenuation provide noisypose estimates compared to those from MR volume registration. Therefore, a scheme was proposedthat, unlike previous techniques, models head motion directly from motion surrogates. Here, a radialbasis function (RBF) regression relates the endogenous tracking signal to the exogenous rigid poseparameters, which are supplied by temporal-sparse MR acquisitions. A proof-of-concept is presentedin which low temporal resolution MR pose estimates are upsampled. The technique is compared tolinear and nearest-neighbour interpolation, and for the regression, both linear and RBF are investigated.The proposed technique was found to introduce some negligible blurring when no motion is present (<0.1 mm mean-of-maximum displacement (MMD)) but reduce blurring by 0.7 mm MMD when motionis present. This demonstrates the capability of the technique to reduce error in motion estimation byimproving the temporal resolution. In a clinical setting, motion correction is likely to become increasingly important in the future. Thework in this thesis will make motion correction easier to apply in a clinical setting, so that it may beapplied more regularly, providing wider benefit.

Deep brain nuclei are closely related to the pathogenesis of neurodegenerative diseases. Automatic segmentation for brain nuclei plays a significant role in aging and disease-related assessment. Quantitative susceptibility mapping (QSM), as a novel MRI imaging technique, attracts increasing attention in deep gray matter (DGM) nuclei-related research and diagnosis. This paper proposes DeepQSMSeg, a deep learning-based end-to-end tool, to segment five pairs of DGM structures from QSM images. The proposed model is based on a 3D encoder-decoder fully convolutional neural network. For concentrating network on the target regions, spatial and channel attention modules are adopted in both encoder and decoder stages. Dice loss is combined with focal loss to alleviate the imbalance of ROI classes. The result shows that our method can segment DGM structures from QSM images precisely, rapidly and reliably. Comparing with ground truth, the average Dice coefficient for all ROIs in the test dataset achieved 0.872±0.053, and Hausdorff distance was 2.644±2.917 mm. Finally, an age-related susceptibility development model was used to confirm the reliability of DeepQSMSeg in aging and disease-related studies.Clinical Relevance-Accurate and automatic segmentation tool for sub-cortical regions in QSM can significantly alleviate the pressure of radiologists. It can also accelerate the progress of related research and clinical translation.

Post-carotid endarterectomy (CEA) cerebral hyperperfusion (CH) can cause intracerebral hemorrhage and cognitive decline. Alterations in susceptibility in response to acetazolamide (ACZ) on 7T MRI quantitative susceptibility mapping (QSM) detect elevated CBV occurring due to impaired cerebrovascular autoregulation. We explored preoperative relative susceptibility changes on 7T MRI QSM in response to ACZ and their ability to predict CH following CEA. Sixty-three patients with uni- or bilateral cervical ICA stenosis of ≥70% underwent 7T MRI at baseline and at 5, 10, 15, and 20 minutes after ACZ administration before surgery. The difference between the susceptibility of venous structures and surrounding brain parenchyma at each time point after ACZ administration relative to the difference at baseline (relative susceptibility difference [RSD]) on QSM images was calculated in the cerebral hemisphere ipsilateral to the surgery site. Brain perfusion SPECT was conducted preoperatively and immediately following CEA to detect postoperative CH (≥100% rise in CBF postoperatively). In 9 patients with postoperative CH, the RSD was significantly increased at 5 or 10 minutes following ACZ administration (P < .05) but was reduced at 15 and 20 minutes (P < .05). In 54 patients without postoperative CH, the SD at all 4 time points after ACZ administration was significantly lower than the baseline value (P < .05). The area under the receiver operating characteristic curve to predict postoperative CH was significantly greater in RSD5 (0.981; 95% CI, 0.910-0.999) than in RSD15 (0.872; 95% CI, 0.764-0.943) (P < .05) or RSD20 (0.780; 95% CI, 0.658-0.874) (P < .01). Sensitivity, specificity, and positive and negative predictive values for RSD5 at a cutoff near the left upper corner of the curve were 100%, 89%, 60%, and 100%, respectively. Logistic regression analysis revealed that only RSD5 significantly predicted postoperative CH (95% CI, 455.9-4043.6; P < .05). Changes in susceptibility on preoperative 7T MRI QSM following ACZ administration predict CH following CEA. Patients with increased RSD5 on pre-CEA 7T MRI QSM following ACZ administration should undergo brain perfusion imaging immediately after surgery. Detection of CH on postoperative brain perfusion imaging warrants intensive blood pressure control.

Iron quantification in Parkinson's disease using an age-based threshold on susceptibility maps: The advantage of local versus entire structure iron content measurements

Multiparametric analysis based on 18F-AV133 PET/MR imaging for clinical application in Parkinson's disease.

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. 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) B1t fields, proton density, T1 , susceptibility and blood flows, facilitating multiple qualitative images and parametric maps. 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 , , proton density (PD), and/or quantitative susceptibility mapping (QSM) values for comparison with reference values or literature. One MULTIPLEX scan offers multiple sets of images, including but not limited to: composited PDW/T1 W/ W, aT1 W, SWI, MRA (optional), B1t map, T1 map, / maps, PD map, and QSM. The quantitative error of phantom T1 , 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. The proposed MUTLIPLEX method possesses great potential for multi-parametric MR imaging.