Browsing by Author "Allen, Jason W."

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    Accelerated model‐based T1, T2* and proton density mapping using a Bayesian approach with automatic hyperparameter estimation
    (Wiley, 2025) Huang, Shuai; Lah, James J.; Allen, Jason W.; Qiu, Deqiang; Radiology and Imaging Sciences, School of Medicine
    Purpose: To achieve automatic hyperparameter estimation for the model-based recovery of quantitative MR maps from undersampled data, we propose a Bayesian formulation that incorporates the signal model and sparse priors among multiple image contrasts. Theory: We introduce a novel approximate message passing framework "AMP-PE" that enables the automatic and simultaneous recovery of hyperparameters and quantitative maps. Methods: We employed the variable-flip-angle method to acquire multi-echo measurements using gradient echo sequence. We explored undersampling schemes to incorporate complementary sampling patterns across different flip angles and echo times. We further compared AMP-PE with conventional compressed sensing approaches such as the l1 norm minimization, PICS and other model-based approaches such as GraSP, MOBA. Results: Compared to conventional compressed sensing approaches such as the l1 -norm minimization and PICS, AMP-PE achieved superior reconstruction performance with lower errors in T*2 mapping and comparable performance in T1 and proton density mappings. When compared to other model-based approaches including GraSP and MOBA, AMP-PE exhibited greater robustness and outperformed GraSP in reconstruction error. AMP-PE offers faster speed than MOBA. AMP-PE performed better than MOBA at higher sampling rates and worse than MOBA at a lower sampling rate. Notably, AMP-PE eliminates the need for hyperparameter tuning, which is a requisite for all the other approaches. Conclusion: AMP-PE offers the benefits of model-based recovery with the additional key advantage of automatic hyperparameter estimation. It works adeptly in situations where ground-truth is difficult to obtain and in clinical environments where it is desirable to automatically adapt hyperparameters to individual protocol, scanner and patient.
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    Langerhans Cell Histiocytosis With Hypothalamic-pituitary and Bone Involvement: A Report of 2 Cases
    (Oxford University Press, 2025-02-10) Giraldi, Erica A.; Allen, Jason W.; McLemore, Morgan L.; Ioachimescu, Adriana G.; Radiology and Imaging Sciences, School of Medicine
    Case 1: A 31-year-old woman presented with secondary amenorrhea, polyuria, and polydipsia. Three years later, magnetic resonance imaging of the brain done for headaches found thickening of the pituitary infundibulum. Laboratory evaluation indicated central vasopressin deficiency, mild hyperprolactinemia, and central hypogonadism. Six months later, progression of the infundibular lesion was documented, now contacting the optic chiasm. Biopsy showed epithelioid histiocytes, chronic inflammation, and gliosis. On postoperative scan, a lesion in the parietal calvaria was identified, which was solitary on a bone scan. The patient received cytarabine for 12 months with resolution of infundibular and bone lesion on positron emission tomography-computed tomography scan 1 year later. Case 2: A 23-year-old man presented with polyuria, polydipsia, and unilateral tinnitus. Laboratory evaluation indicated vasopressin deficiency and central hypogonadism. External ear canal biopsy indicated an infiltrative lesion with eosinophils, small lymphocytes and histiocytes. Magnetic resonance of the brain revealed hypothalamic/infundibular and parietal and mastoid bone lesions; no other lesions were identified on positron emission tomography-computed tomography. Patient received cytarabine for 1 year with resolution of lesions, which was maintained during follow-up of 4 years. Although rare, Langerhans cell histiocytosis in adults should be considered in the appropriate clinical scenario. Multidisciplinary treatment is required.