L. L. Tsai

3He lung imaging in an open access, very-low-field human magnetic resonance imaging system

The human lung and its functions are extremely sensitive to gravity; however, the conventional high‐field magnets used for most laser‐polarized 3He MRI of the human lung restrict subjects to lying horizontally. Imaging of human lungs using inhaled laser‐polarized 3He gas is demonstrated in an open‐access very‐low‐magnetic‐field (<5 mT) MRI instrument. This prototype device employs a simple, low‐cost electromagnet, with an open geometry that allows variation of the orientation of the imaging subject in a two‐dimensional plane. As a demonstration, two‐dimensional lung images were acquired with 4‐mm in‐plane resolution from a subject in two orientations: lying supine and sitting in a vertical position with one arm raised. Experience with this prototype device will guide optimization of a second‐generation very‐low‐field imager to enable studies of human pulmonary physiology as a function of subject orientation. Magn Reson Med 53:745–749, 2005.

An Open-Access, Very-Low-Field MRI System for Posture-Dependent 3He Human Lung Imaging

We describe the design and operation of an open-access, very-low-field, magnetic resonance imaging (MRI) system for in vivo hyperpolarized 3He imaging of the human lungs. This system permits the study of lung function in both horizontal and upright postures, a capability with important implications in pulmonary physiology and clinical medicine, including asthma and obesity. The imager uses a bi-planar B(0) coil design that produces an optimized 65 G (6.5 mT) magnetic field for 3He MRI at 210 kHz. Three sets of bi-planar coils produce the x, y, and z magnetic field gradients while providing a 79-cm inter-coil gap for the imaging subject. We use solenoidal Q-spoiled RF coils for operation at low frequencies, and are able to exploit insignificant sample loading to allow for pre-tuning/matching schemes and for accurate pre-calibration of flip angles. We obtain sufficient SNR to acquire 2D 3He images with up to 2.8mm resolution, and present initial 2D and 3D 3He images of human lungs in both supine and upright orientations. 1H MRI can also be performed for diagnostic and calibration reasons.

Turing patterns in a self-replicating mechanism with a self-complementary template

A variety of nonlinear chemical models, such as the Selkov–Schnakenberg, exhibit Turing patterns. The Templator, which is based on a minimal autocatalytic monomer–dimer system, is a newer two-variable model also able to show Turing patterns. Here we find that the dynamic behavior of the Templator is quite similar to other models with cubic nonlinearities. This is demonstrated through a series of computer simulations in two dimensions utilizing the cellular automata approach. The selection of parameter values is based on linear stability analysis, which provides a relatively simple method of predicting Turing pattern formation. The simulations reveal spot, labyrinth, and striped patterns, in agreement with the predictions of the analysis. Other behaviors, such as honeycomb patterns, are also observed. For some parameter values, we study transient spot replication. Our findings strongly suggest that the Templator may belong to the same class of models previously studied by Pearson.

Interstitial gas and density segregation of vertically vibrated granular media

We report experimental studies of the effect of interstitial gas on mass-density segregation in a vertically vibrated mixture of equal-sized bronze and glass spheres. Sufficiently strong vibration in the presence of interstitial gas induces vertical segregation into sharply separated bronze and glass layers. We find that the segregated steady state (i.e., bronze or glass layer on top) is a sensitive function of gas pressure and viscosity, as well as vibration frequency and amplitude. In particular, we identify distinct regimes of behavior that characterize the change from bronze-on-top to glass-on-top steady state.

Sources of Apical Defects on a High-Sensitivity Cardiac Camera: Experiences from a Practice Performance Assessment

Apical perfusion artifacts seen on a high-sensitivity camera warranted a practice performance assessment to evaluate contributions from soft-tissue attenuation, patient positioning, and image processing techniques. Methods: Cardiac perfusion studies (n = 534) spanning 5 mo were retrospectively reviewed. Images were acquired with the patient in the upright position, and attenuation correction was used. Regression analysis and contingency tables correlated clinical data to the presence of apical artifacts. Results: There was a positive correlation of with female sex (χ2 = 32, P < 0.001), degree of overlying soft tissues (χ2 = 20, P < 0.002), and breast cleavage (χ2 = 7, P < 0.008) and a negative correlation with angiography-confirmed disease (χ2 = 6, P < 0.02). There was moderate interobserver agreement between 2 observers in determining the presence of apical defects (κ= 0.44, 95% confidence interval = 0.19–0.69), and there was a perceived improvement of apical defects using fewer iterative updates (χ2 = 8, P < 0.003). Conclusion: An understanding of sources contributing to imaging artifacts is a crucial portion of quality assessment in radiology and nuclear medicine. A practice performance assessment study at our institution showed that apical artifacts on a new-generation cardiac camera can be partially attributed to overlying soft-tissue attenuation and ameliorated by altering the reconstruction.

Alpha-fetoprotein (AFP) as tumor marker in a patient with urothelial cancer with exceptional response to anti-PD-1 therapy and an escape lesion mimic

The development of a new lesion in a patient with a complete remission to anti-PD-1 therapy is highly concerning for a drug resistant escape lesion. Here, we present a case of a 62-year-old patient with chemotherapy-resistant metastatic urothelial cancer who had a complete remission to pembrolizumab. The patient’s disease burden tracked closely to serum levels of alpha-fetoprotein (AFP) expressed by the tumor and served as an accurate tumor marker. Surveillance imaging revealed a solitary growing pulmonary nodule mimicking an escape lesion in the absence of an increase in AFP levels. Biopsy of this lesion revealed a benign intraparenchymal lymph node with no evidence of metastatic carcinoma. This case indicates that in some patients, biomarkers aberrantly expressed by their tumors, such as AFP in this patient, may be used as a tumor marker for response to anti-PD-1 therapy and emphasizes the importance of confirming potential escape lesions by pathologic examination.

Vaginal spindle cell epithelioma: A first complete MRI and histopathologic description

Spindle cell epithelioma of the vagina is a benign entity with fewer than sixty cases described in the literature, and only two with limited imaging findings, since the early 1950s. Early pathology literature suggested the lesions were mixed tumors of myoepithelial origin, but subsequent studies have found relatively few immunohistochemical characteristics in common with other mixed cell tumors. More recently, Mullerian, urogenital sinus epithelial, and pluripotential cell origins have been proposed. Given lesion rarity and a typical lack of imaging before excision, the imaging appearance of vaginal spindle cell epitheliomas has not been fully described in the radiology literature, and without comprehensive pathology correlation. The authors describe a case of spindle cell epithelioma in a 54-year-old woman which was incidentally discovered on MRI performed for uterine fibroid embolization planning. Pathology and immunohistochemistry confirmed the diagnosis.

Gallbladder splenosis: a hereto unreported mimicker of a gallbladder neoplasm.

Splenosis is a completely benign entity that can mimic a primary mass or metastasis. Herein we report the first known case of gallbladder splenosis in a 49-year-old woman with an extensive surgical and medical history. Cross-sectional computed tomography and MRI demonstrated a single mass arising from the gallbladder fundus. Revelation of splenectomy, confirmed to be traumatic from medical records, raised the suspicion for splenosis. The diagnosis was confirmed with a Technecium-99m-labeled heat-damaged blood cell scan, considered the gold-standard for detection of ectopic splenic tissue.