Correlation of Pancreatic T1 Values Using Modified Look-Locker Inversion Recovery Sequence (MOLLI) with Pancreatic Exocrine and Endocrine Function

Whole pancreas water T1 mapping at 3 Tesla

PURPOSE

A fast T1 mapping method of the whole pancreas remains a challenge, due to the complex anatomy of the organ. In addition, a technique for pancreas water T1 mapping is needed, since the T1 is biased in the presence of fat. The purpose of this work is to accelerate the acquisition of water selective T1 (wT1) mapping for the whole pancreas at 3 T.

METHODS

The proposed method combines a continuous inversion-recovery Look-Locker acquisition with a single-shot gradient echo spiral readout, water-fat separation and dictionary matching for wT1 mapping of the whole pancreas at 3 T. The bias of T1 in the presence of fat was evaluated in a phantom by comparing the modified Look-Locker inversion-recovery (MOLLI) and the proposed method to MRS measurements. The present method was validated in 11 volunteers by evaluating its pancreas coverage and repeatability and by comparing it to MOLLI. Four pancreatitis patients were evaluated using the proposed method and clinical scans.

RESULTS

The phantom wT1 results are in better agreement to MRS (wT 1 = 1.02 *wT 1 MRS - 47.81 , R 2 = 0.99 ) than MOLLI (T 1 MOLLI = 1.13 ∗ wT 1 MRS - 74.65 , R 2 = 0.98 ) . The volunteer wT1 results demonstrate the whole pancreas coverage capability for different fat fractions, good repeatability (wT 1 , 2 ∘ = 0.98 ∗ wT 1 , 1 ∘ + 17.40 , R 2 = 0.69 ) and lower T1 values than MOLLI (wT 1 = 0.34 *T 1 MOLLI + 383.65 , R 2 = 0.26 ) . The wT1 maps in patients captured diverse pancreatitis regions with higher values ( wT 1 Patients = 831 - 1696 ms ) than in the volunteerswT 1 Volunteers = 605 - 799 ms , thus showing their potential clinical feasibility.

CONCLUSION

The present work proposes a wT1 mapping methodology of the whole pancreas at 3 T, where 24 slices ( 2 × 2 × 5 mm 3 ) were acquired in three short breath-holds of 12 s each.

T1 Mapping of the Abdomen, From the AJR "How We Do It" Special Series

By exploiting different tissues' characteristic T1 relaxation times, T1-weighted images help distinguish normal and abnormal tissues, aiding assessment of diffuse and local pathologies. However, such images do not provide quantitative T1 values. Advances in abdominal MRI techniques have enabled measurement of abdominal organs' T1 relaxation times, which can be used to create color-coded quantitative maps. T1 mapping is sensitive to tissue microenvironments including inflammation and fibrosis and has received substantial interest for noninvasive imaging of abdominal organ pathology. In particular, quantitative mapping provides a powerful tool for evaluation of diffuse disease by making apparent changes in T1 occurring across organs that may otherwise be difficult to identify. Quantitative measurement also facilitates sensitive monitoring of longitudinal T1 changes. Increased T1 in liver helps to predict parenchymal fibro-inflammation, in pancreas is associated with reduced exocrine function from chronic or autoimmune pancreatitis, and in kidney is associated with impaired renal function and aids diagnosis of chronic kidney disease. In this review, we describe the acquisition, postprocessing, and analysis of T1 maps in the abdomen and explore applications in liver, spleen, pancreas, and kidney. We highlight practical aspects of implementation and standardization, technical pitfalls and confounding factors, and areas of likely greatest clinical impact.

Quantitative Imaging Reveals Steatosis and Fibroinflammation in Multiple Organs in People With Type 2 Diabetes: A Real-World Study

We aimed to determine the extent of multiorgan fat accumulation and fibroinflammation in individuals living with type 2 diabetes. We deeply phenotyped individuals with type 2 diabetes (134 from secondary care, 69 from primary care) with multiorgan, quantitative, multiparametric MRI and compared with 134 matched control individuals without diabetes and 92 control individuals with normal weight. We examined the impact of diabetes duration, obesity status, and glycemic control. Ninety-three of the individuals with type 2 diabetes were reevaluated at 7 months (median). Multiorgan abnormalities were more common in individuals with type 2 diabetes (94%) than in age- and BMI-matched healthy individuals or healthy individuals with normal weight. We demonstrated a high burden of combined steatosis and fibroinflammation within the liver, pancreas, and kidneys (41%, 17%, and 10%) associated with visceral adiposity (73%) and poor vascular health (82%). Obesity was most closely associated with advanced liver disease, renal and visceral steatosis, and multiorgan abnormalities, while poor glycemic control was associated with pancreatic fibroinflammation. Pharmacological therapies with proven cardiorenal protection improved liver and vascular health unlike conventional glucose-lowering treatments, while weight loss or improved glycemic control reduced multiorgan adiposity (P ≤ 0.01). Quantitative imaging in people with type 2 diabetes highlights widespread organ abnormalities and may provide useful risk and treatment stratification.

ARTICLE HIGHLIGHTS

Noninvasive assessment of organ-specific and shared pathways in multi-organ fibrosis using T1 mapping

Fibrotic diseases affect multiple organs and are associated with morbidity and mortality. To examine organ-specific and shared biologic mechanisms that underlie fibrosis in different organs, we developed machine learning models to quantify T1 time, a marker of interstitial fibrosis, in the liver, pancreas, heart and kidney among 43,881 UK Biobank participants who underwent magnetic resonance imaging. In phenome-wide association analyses, we demonstrate the association of increased organ-specific T1 time, reflecting increased interstitial fibrosis, with prevalent diseases across multiple organ systems. In genome-wide association analyses, we identified 27, 18, 11 and 10 independent genetic loci associated with liver, pancreas, myocardial and renal cortex T1 time, respectively. There was a modest genetic correlation between the examined organs. Several loci overlapped across the examined organs implicating genes involved in a myriad of biologic pathways including metal ion transport (SLC39A8, HFE and TMPRSS6), glucose metabolism (PCK2), blood group antigens (ABO and FUT2), immune function (BANK1 and PPP3CA), inflammation (NFKB1) and mitosis (CENPE). Finally, we found that an increasing number of organs with T1 time falling in the top quintile was associated with increased mortality in the population. Individuals with a high burden of fibrosis in ≥3 organs had a 3-fold increase in mortality compared to those with a low burden of fibrosis across all examined organs in multivariable-adjusted analysis (hazard ratio = 3.31, 95% confidence interval 1.77-6.19; P = 1.78 × 10-4). By leveraging machine learning to quantify T1 time across multiple organs at scale, we uncovered new organ-specific and shared biologic pathways underlying fibrosis that may provide therapeutic targets.

T1 and T2-mapping in pancreatic MRI: Current evidence and future perspectives

Conventional T1- and T2-weighted magnetic resonance imaging (MRI) of the pancreas can vary significantly due to factors such as scanner differences and pulse sequence variations. This review explores T1 and T2 mapping techniques, modern MRI methods providing quantitative information about tissue relaxation times. Various T1 and T2 mapping pulse sequences are currently under investigation. Clinical and research applications of T1 and T2 mapping in the pancreas include their correlation with fibrosis, inflammation, and neoplasms. In chronic pancreatitis, T1 mapping and extracellular volume (ECV) quantification demonstrate potential as biomarkers, aiding in early diagnosis and classification. T1 mapping also shows promise in evaluating pancreatic exocrine function and detecting glucose metabolism disorders. T2* mapping is valuable in quantifying pancreatic iron, offering insights into conditions like thalassemia major. However, challenges persist, such as the lack of consensus on optimal sequences and normal values for healthy pancreas relaxometry. Large-scale studies are needed for validation, and improvements in mapping sequences are essential for widespread clinical integration. The future holds potential for mixed qualitative and quantitative models, extending the applications of relaxometry techniques to various pancreatic lesions and enhancing routine MRI protocols for pancreatic pathology diagnosis and prognosis.

Quantitative Magnetic Resonance Imaging for the Pancreas: Current Status

ABSTRACT

Magnetic resonance imaging (MRI) is important for evaluating pancreatic disorders, and anatomical landmarks play a major role in the interpretation of results. Quantitative MRI is an effective diagnostic modality for various pathologic conditions, as it allows the investigation of various physical parameters. Recent advancements in quantitative MRI techniques have significantly improved the accuracy of pancreatic MRI. Consequently, this method has become an essential tool for the diagnosis, treatment, and monitoring of pancreatic diseases. This comprehensive review article presents the currently available evidence on the clinical utility of quantitative MRI of the pancreas.

Quantitative abdominal magnetic resonance imaging in children-special considerations

The use of quantitative MRI methods for assessment of the abdomen in children has become commonplace over the past decade. Increasingly employed methods include MR elastography, chemical shift encoded (CSE) MR imaging for determination of proton density fat fraction, diffusion-weighted imaging, and a variety of relaxometry techniques, such as T1 and T2* mapping. These techniques can be used in a variety of settings to distinguish normal from abnormal tissue as well as determine the severity of disease. The performance of quantitative MRI methods in the pediatric population presents unique challenges as compared to adult populations. These challenges relate to multiple factors, including patient size, pediatric physiology, inability to breath hold, and greater physical motion during the examination. The purpose of this review article is to review quantitative MRI methods that may be used in clinical practice to assess the pediatric abdomen and to discuss special considerations when performing these techniques in children.

Dual flip-angle IR-FLASH with spin history mapping for B1+ corrected T1 mapping: Application to T1 cardiovascular magnetic resonance multitasking

PURPOSE

To develop a single-scan method for B 1 + -corrected T1 mapping and apply it for free-breathing (FB) cardiac MR multitasking without electrocardiogram (ECG) triggering.

METHODS

One dual flip-angle (2FA) inversion recovery (IR)-FLASH scan provides two observations of T 1 ∗ (apparent T1 ) corresponding to two distinct combinations of the nominal FA α and B 1 + . Spatiotemporally coregistered T1 and B 1 + spin history maps are obtained by fitting the 2FA signal model. T1 estimate accuracy and repeatability for single flip-angle (1FA) and 2FA IR-FLASH sequence MR multitasking were evaluated at 3T. A T1 phantom was first imaged on the scanner table, then on two human subjects' thoraxes in both breath-hold (BH) and FB conditions. IR-turbo spin echo (IR-TSE) static phantom T1 measurements served as reference. In 10 healthy subjects, myocardial T1 was evaluated with ECG-free, FB multitasking sequences alongside ECG-triggered BH MOLLI.

RESULTS

For phantom-on-table T1 estimates, 2FA agreed better with IR-TSE (intraclass correlation coefficient [ICC] = 0.996, mean error ± SD = -1.6% ± 1.9%) than did 1FA (ICC = 0.922; mean error ± SD = -4.3% ± 12%). For phantom-on-thorax, 2FA was more repeatable and robust to respiration than 1FA (coefficient of variation [CoV] = 1.2% 2FA, = 11.3% 1FA). In vivo, in intrasession T1 repeatability, 2FA (septal CoV = 2.4%, six-segment CoV = 4.4%) outperformed 1FA (septal CoV = 3.1%, six-segment CoV = 5.5%). In six-segment T1 homogeneity, 2FA (CoV = 7.9%) also outperformed 1FA (CoV = 11.1%).

CONCLUSION

The 2FA IR-FLASH improves T1 estimate accuracy and repeatability over 1FA IR-FLASH, and enables single-scan B 1 + -corrected T1 mapping without BHs or ECG when used with MR multitasking.