Creating the freedom to thrive: Honoring the legacy of RSNA gold medalist, Deborah Levine, MD

Awarded the Radiological Society of North America (RSNA) Gold Medal in 2018, Dr. Deborah Levine's research, journalism, and mentorship have left an indelible mark on the radiology field. Her work in ultrasound led to its use as the standard for monitoring benign adnexal cysts. She helped popularize obstetric magnetic resonance imaging (MRI) through her research on its use in placental accreta and fetal abnormalities, which led to the development of the 'Compendium of Fetal MRI' website. This work in research led naturally to a career in journalism, where she eventually became Senior Deputy Editor of Radiology and founded Radiology Select. Concurrently with her personal achievements, Dr. Levine has dedicated herself to the mentorship of her female trainees. She sought various leadership positions to learn more about and advocate for the promotion and support of female leadership in radiology departments. In many ways, Dr. Levine's career and work have transformed radiology as we know it today for both patients and physicians.

A Practical Guide for Paid Family and Medical Leave in Radiology, From the AJR Special Series on DEI

Paid family and medical leave (FML) has significant benefits to organizations, including improvements in employee recruitment and retention, workplace culture, and employee morale and productivity, and is supported by evidence for overall cost savings. Furthermore, paid FML related to childbirth has significant benefits to individuals and families, including but not limited to improved maternal and infant health outcomes and improved breastfeeding initiation and duration. In the case of nonchildbearing parental leave, paid FML is associated with more equitable long-term division of household labor and childcare. Paid FML is increasingly being recognized as an important issue in medicine, as evidenced by the recent passage of policies by national societies and governing bodies, including the American Board of Medical Specialties, American Board of Radiology, Accreditation Council for Graduate Medical Education (ACGME), American College of Radiology, and American Medical Association. Implementation of paid FML requires adherence to federal, state, and local laws as well as institutional requirements. Specific requirements pertain to trainees from national governing bodies, such as the ACGME and medical specialty boards. Flexibility, work coverage, culture, and finances are additional considerations for ensuring an optimal paid FML policy that accounts for concerns of all impacted individuals.

Deep learning based automated delineation of the intraprostatic gross tumour volume in PSMA-PET for patients with primary prostate cancer

PURPOSE

With the increased use of focal radiation dose escalation for primary prostate cancer (PCa), accurate delineation of gross tumor volume (GTV) in prostate-specific membrane antigen PET (PSMA-PET) becomes crucial. Manual approaches are time-consuming and observer dependent. The purpose of this study was to create a deep learning model for the accurate delineation of the intraprostatic GTV in PSMA-PET.

METHODS

A 3D U-Net was trained on 128 different 18F-PSMA-1007 PET images from three different institutions. Testing was done on 52 patients including one independent internal cohort (Freiburg: n = 19) and three independent external cohorts (Dresden: n = 14 18F-PSMA-1007, Boston: Massachusetts General Hospital (MGH): n = 9 18F-DCFPyL-PSMA and Dana-Farber Cancer Institute (DFCI): n = 10 68Ga-PSMA-11). Expert contours were generated in consensus using a validated technique. CNN predictions were compared to expert contours using Dice similarity coefficient (DSC). Co-registered whole-mount histology was used for the internal testing cohort to assess sensitivity/specificity.

RESULTS

Median DSCs were Freiburg: 0.82 (IQR: 0.73-0.88), Dresden: 0.71 (IQR: 0.53-0.75), MGH: 0.80 (IQR: 0.64-0.83) and DFCI: 0.80 (IQR: 0.67-0.84), respectively. Median sensitivity for CNN and expert contours were 0.88 (IQR: 0.68-0.97) and 0.85 (IQR: 0.75-0.88) (p = 0.40), respectively. GTV volumes did not differ significantly (p > 0.1 for all comparisons). Median specificity of 0.83 (IQR: 0.57-0.97) and 0.88 (IQR: 0.69-0.98) were observed for CNN and expert contours (p = 0.014), respectively. CNN prediction took 3.81 seconds on average per patient.

CONCLUSION

The CNN was trained and tested on internal and external datasets as well as histopathology reference, achieving a fast GTV segmentation for three PSMA-PET tracers with high diagnostic accuracy comparable to manual experts.

COVID-19: Findings in nuclear medicine from head to toe

COVID-19 is a multisystemic disease, and hence its potential manifestations on nuclear medicine imaging can extend beyond the lung. Therefore, it is important for the nuclear medicine physician to recognize these manifestations in the clinic. While FDG-PET/CT is not indicated routinely in COVID-19 evaluation, its unique capability to provide a functional and anatomical assessment of the entire body means that it can be a powerful tool to monitor acute, subacute, and long-term effects of COVID-19. Single-photon scintigraphy is routinely used to assess conditions such as pulmonary embolism, cardiac ischemia, and thyroiditis, and COVID-19 may present in these studies. The most common nuclear imaging finding of COVID-19 vaccination to date is hypermetabolic axillary lymphadenopathy. This may pose important diagnostic and management dilemmas in oncologic patients, particularly those with malignancies where the axilla constitutes a lymphatic drainage area. This article aims to summarize the relevant literature published since the beginning of the pandemic on the intersection between COVID-19 and nuclear medicine.

Standard Adult Gastric Emptying Scintigraphy Criteria Is Applicable for Partial Meal Ingestion

BACKGROUND/AIMS

Gastric emptying scintigraphy is commonly performed to assess for dysmotility. A standardized meal with associated threshold criteria was established in 2000 to enable robust interpretation. However, no guidance is available to interpret results when patients do not ingest the entire meal. The purpose of this study is to determine the continued appropriateness of the threshold criteria in contemporary clinical practice and its relevance for partially ingested meals.

METHODS

This retrospective study analyzed patients (n = 1365 total) who underwent solid-phase gastric emptying scintigraphy at an academic medical center. Patients were stratified based on their completion of the standard meal. Patients were further stratified into normal and delayed gastric emptying cohorts based on the current criteria. Percent gastric retention values at 1, 2, 3, and 4 h were compared.

RESULTS

Median (95% upper reference) normal gastric retention values for the complete standard meal were 64% (87%) at 1 h, 25% (60%) at 2 h, 13% (54%) at 3 h and 4% (9%) at 4 h. Consumption of at least 50% of the standard meal yielded similar retention; 53% (86%) at 1 h, 19% (58%) at 2 h, 6% (29%) at 3 h and 3% (10%) at 4 h. There was no significant age- or gender-specific differences using the current criteria, and no differences were observed based on diabetic status. Retention values matched well with the current criteria and validated with data-driven clustering.

CONCLUSION

Adult normative standards for gastric emptying scintigraphy are appropriate for differentiating normal and delayed populations and can be applied to partial meals with at least 50% completion.

Key Factors to Attract More U.S. Diagnostic Radiology Residents into the Field of Nuclear Medicine and Molecular Imaging: A National Survey

RATIONALE AND OBJECTIVES

To understand the current state of radiology residents' exposure to nuclear medicine and molecular imaging (NM/MI), determine key factors that may attract more trainees into the field, and identify differentiating aspects between those specializing in NM/MI and those who are not.

MATERIALS AND METHODS

An anonymous web-based survey was sent to contacts at all diagnostic radiology residency programs in the United States for dissemination to their residents, collecting information about trainees' NM/MI exposure during residency and factors that may attract them to NM/MI.

RESULTS

A total of 198 trainees responded to the survey, 34 of whom plan on pursuing a career in NM/MI. Most trainees reported early exposure to NM/MI during residency; most (97.4%) reported ample exposure to general NM/MI and oncologic studies. Less than 3% of trainees reported adequate exposure to therapies, neurological applications, molecular imaging/research advances, and physics. Respondents reported a need for better quality education (38.9%) and exposure to mentors (28.8%) as ways to attract trainees to NM/MI. Routinely encountered clinical pathology was the most interesting for those specializing in NM/MI (29.4%), whereas lifestyle was the most attractive aspect of NM/MI for those not pursuing a career in the field (27.4%). NM/MI-associated research was the least attractive for those specializing in NM/MI (35.3%), while job market concerns was the least attractive aspect for those not specializing in NM/MI (37.2%). Trainees planning to specialize in NM/MI reported higher satisfaction with their orientation to NM/MI during their first clinical rotation compared to those who do not plan to specialize in the field (3.03/5.00 and 2.67/5.00, respectively, p = 0.04).

CONCLUSION

This survey highlights several factors that training programs and national societies can target to improve interest in NM/MI among radiology residents. We found that optimized education initiatives, including improved orientation to the field, increased mentoring, and career opportunities are essential levers for recruiting radiology trainees into the NM/MI workforce.

Overcoming differential tumor penetration of BRAF inhibitors using computationally guided combination therapy

BRAF-targeted kinase inhibitors (KIs) are used to treat malignancies including BRAF-mutant non-small cell lung cancer, colorectal cancer, anaplastic thyroid cancer, and, most prominently, melanoma. However, KI selection criteria in patients remain unclear, as are pharmacokinetic/pharmacodynamic (PK/PD) mechanisms that may limit context-dependent efficacy and differentiate related drugs. To address this issue, we imaged mouse models of BRAF-mutant cancers, fluorescent KI tracers, and unlabeled drug to calibrate in silico spatial PK/PD models. Results indicated that drug lipophilicity, plasma clearance, faster target dissociation, and, in particular, high albumin binding could limit dabrafenib action in visceral metastases compared to other KIs. This correlated with retrospective clinical observations. Computational modeling identified a timed strategy for combining dabrafenib and encorafenib to better sustain BRAF inhibition, which showed enhanced efficacy in mice. This study thus offers principles of spatial drug action that may help guide drug development, KI selection, and combination.

Probing immune infiltration dynamics in cancer by in vivo imaging

Cancer immunotherapies typically aim to stimulate the accumulation and activity of cytotoxic T-cells or pro-inflammatory antigen-presenting cells, reduce immunosuppressive myeloid cells or regulatory T-cells, or elicit some combination of effects thereof. Notwithstanding the encouraging results, immunotherapies such as PD-1/PD-L1-targeted immune checkpoint blockade act heterogeneously across individual patients. It remains challenging to predict and monitor individual responses, especially across multiple sites of metastasis or sites of potential toxicity. To address this need, in vivo imaging of both adaptive and innate immune cell populations has emerged as a tool to quantify spatial leukocyte accumulation in tumors non-invasively. Here we review recent progress in the translational development of probes for in vivo leukocyte imaging, focusing on complementary perspectives provided by imaging of T-cells, phagocytic macrophages, and their responses to therapy.

Confocal Imaging of Single-Cell Signaling in Orthotopic Models of Ovarian Cancer

Ovarian cancer (OVCA) is frequently detected at late stages of disease, often with dissemination throughout the peritoneal cavity surface, abdomen, and ascites fluid. Tumor signaling via mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K) pathways can promote OVCA progression and depend on local microenvironmental cues. To better study OVCA in situ within native tissue contexts, here we describe confocal microscopy techniques to image mouse models of intraperitoneal disease at a single-cell resolution. As a proof of principle demonstration, examples are highlighted for simultaneously imaging tumor vascularization, infiltrating and often immunosuppressive immune cells (tumor-associated macrophages), and OVCA kinase activity.

Medical Specialty Board Parental, Caregiver, and Medical Leave Policy Updates After 2021 American Board of Medical Specialties Mandate

This study assesses how member boards of the American Board of Medical Specialties (ABMS) have adhered to a 2021 ABMS policy change allowing residents a minimum of 6 weeks of parental, caregiver, and medical leave.

Incorporating PSMA-Targeting Theranostics Into Personalized Prostate Cancer Treatment: a Multidisciplinary Perspective

Recent developments in prostate-specific membrane antigen (PSMA) targeted diagnostic imaging and therapeutics (theranostics) promise to advance the management of primary, biochemically recurrent, and metastatic prostate cancer. In order to maximize the clinical impact of PSMA-targeted theranostics, a coordinated approach between the clinical stakeholders involved in prostate cancer management is required. Here, we present a vision for multidisciplinary use of PSMA theranostics from the viewpoints of nuclear radiology, medical oncology, urology, and radiation oncology. We review the currently available and forthcoming PSMA-based imaging and therapeutics and examine current and potential impacts on prostate cancer management from early localized disease to advanced treatment-refractory disease. Finally, we highlight the clinical and research opportunities related to PSMA-targeted theranostics and describe the importance of multidisciplinary collaboration in this space.

Therapeutically reprogrammed nutrient signalling enhances nanoparticulate albumin bound drug uptake and efficacy in KRAS-mutant cancer

Nanoparticulate albumin bound paclitaxel (nab-paclitaxel, nab-PTX) is among the most widely prescribed nanomedicines in clinical use, yet it remains unclear how nanoformulation affects nab-PTX behaviour in the tumour microenvironment. Here, we quantified the biodistribution of the albumin carrier and its chemotherapeutic payload in optically cleared tumours of genetically engineered mouse models, and compared the behaviour of nab-PTX with other clinically relevant nanoparticles. We found that nab-PTX uptake is profoundly and distinctly affected by cancer-cell autonomous RAS signalling, and RAS/RAF/MEK/ERK inhibition blocked its selective delivery and efficacy. In contrast, a targeted screen revealed that IGF1R kinase inhibitors enhance uptake and efficacy of nab-PTX by mimicking glucose deprivation and promoting macropinocytosis via AMPK, a nutrient sensor in cells. This study thus shows how nanoparticulate albumin bound drug efficacy can be therapeutically improved by reprogramming nutrient signalling and enhancing macropinocytosis in cancer cells.

Pediatric Solid Gastric Emptying Scintigraphy: Normative Value Guidelines and Nonstandard Meal Alternatives

INTRODUCTION

Adult standards for gastric emptying scintigraphy, including the type of meal and range of normative values for percent gastric emptying, are routinely used in pediatric practice, but to date have not been validated. The purpose of this study is to determine whether the use of adult criteria for gastric emptying scintigraphy is valid for children and whether alternative nonstandard meals can also be offered based on these criteria.

METHODS

This retrospective study analyzed patients (n = 1,151 total) who underwent solid-phase gastric emptying scintigraphy. Patients were stratified into normal and delayed gastric emptying cohorts based on adult criteria, i.e., with normal gastric emptying defined as ≤10% gastric retention at 4 hours. Patients were further stratified based on the type of meal, namely complete or partial adult standard meals or alternative cheese-based meals. Percent gastric retention values at 1, 2, 3, and 4 hours were compared.

RESULTS

The median (95% upper reference limit) percentage gastric retention values for the complete standard meal were 72% (93%) at 1 hour, 39% (65%) at 2 hours, 15% (33%) at 3 hours, and 6% (10 %) at 4 hours. By comparison, the values for cheese-based meals were 60% (87%) at 1 hour, 29% (61%) at 2 hours, 10% (30%) at 3 hours, and 5% (10%) at 4 hours. Consumption of at least 50% of the standard meal yielded similar retention percentages; 68% (89%) at 1 hour, 32% (57%) at 2 hours, 10% (29%) at 3 hours, and 5% (10%) at 4 hours. There were no significant age- or sex-specific differences using the adult criteria.

DISCUSSION

The adult normative standards for gastric emptying scintigraphy are applicable for use in the pediatric population. These same standards can be also be applied to nonstandard meal options, including cheese-based alternative meals and partial standard meals.

Quantitative assessment of pulmonary function in lymphangioleiomyomatosis patients using high-resolution computed tomography and pulmonary function tests

Background

To explore the feasibility of using quantitative high-resolution computed tomography (HRCT) to evaluate pulmonary function in patients with pulmonary lymphangioleiomyomatosis (PLAM).

Methods

Pulmonary function tests (PFTs) were performed in 30 patients with pathologically confirmed PLAM with the use of HRCT. These results were correlated with quantitative HRCT in 21 patients.

Results

There were significant correlations between the HRCT parameters for lung function and PFT parameters. Among these parameters, emphysema volume (EV), pulmonary volume with a pixel index less than the trigger threshold (−950 HU) to account for a proportion of total lung volume [PI-950 (%)] and forced expiratory volume in 1 second/forced vital capacity [FEV1/FVC (%)] had the strongest correlations, reaching values between −0.71 and −0.68. HRCT lung function might therefore also be helpful for predicting changes in lung function before and after treatment.

Conclusions

HRCT is helpful for the assessment of pulmonary function in PLAM patients and can assist in the clinical evaluation of lung function and treatment response in patients with this disease.

Receptor-Driven ERK Pulses Reconfigure MAPK Signaling and Enable Persistence of Drug-Adapted BRAF-Mutant Melanoma Cells

Targeted inhibition of oncogenic pathways can be highly effective in halting the rapid growth of tumors but often leads to the emergence of slowly dividing persister cells, which constitute a reservoir for the selection of drug-resistant clones. In BRAF^V600E melanomas, RAF and MEK inhibitors efficiently block oncogenic signaling, but persister cells emerge. Here, we show that persister cells escape drug-induced cell-cycle arrest via brief, sporadic ERK pulses generated by transmembrane receptors and growth factors operating in an autocrine/paracrine manner. Quantitative proteomics and computational modeling show that ERK pulsing is enabled by rewiring of mitogen-activated protein kinase (MAPK) signaling: from an oncogenic BRAF^V600E monomer-driven configuration that is drug sensitive to a receptor-driven configuration that involves Ras-GTP and RAF dimers and is highly resistant to RAF and MEK inhibitors. Altogether, this work shows that pulsatile MAPK activation by factors in the microenvironment generates a persistent population of melanoma cells that rewires MAPK signaling to sustain non-genetic drug resistance.

Detecting Immune Response to Therapies Targeting PDL1 and BRAF by Using Ferumoxytol MRI and Macrin in Anaplastic Thyroid Cancer

Background Anaplastic thyroid cancer (ATC) is aggressive with a poor prognosis, partly because of the immunosuppressive microenvironment created by tumor-associated macrophages (TAMs). Purpose To understand the relationship between TAM infiltration, tumor vascularization, and corresponding drug delivery by using ferumoxytol-enhanced MRI and macrin in an ATC mouse model. Materials and Methods ATC tumors were generated in 6-8-week-old female B6129SF1/J mice through intrathyroid injection to model orthotopic tumors, or intravenously to model hematogenous metastasis, and prospectively enrolled randomly into treatment cohorts (n = 94 total; August 1, 2018, to January 15, 2020). Mice were treated with vehicle or combined serine/threonine-protein kinase B-Raf (BRAF) kinase inhibitor (BRAFi) and anti-PDL1 antibody (aPDL1). A subset was cotreated with therapies, including an approximately 70-nm model drug delivery nanoparticle (DDNP) to target TAM, and an antibody-neutralizing colony stimulating factor 1 receptor (CSF1R). Imaging was performed at the macroscopic level with ferumoxytol-MRI and microscopically with macrin. Genetically engineered Braf^V600E/WT p53-null allografts were used and complemented by a GFP-transgenic derivative and human xenografts. Tumor-bearing organs were processed by using tissue clearing and imaged with confocal microscopy and MRI. Two-tailed Wilcoxon tests were used for comparison (≥five per group). Results TAM levels were higher in orthotopic thyroid tumors compared with pulmonary metastatic lesions by 79% ± 23 (standard deviation; P < .001). These findings were concordant with ferumoxytol MRI, which showed 136% ± 88 higher uptake in thyroid lesions (P = .02) compared with lung lesions. BRAFi and aPDL1 combination therapy resulted in higher tumor DDNP delivery by 39% ± 14 in pulmonary lesions (P = .004). Compared with the untreated group, tumors following BRAFi, aPDL1, and CSF1R-blocking antibody combination therapy did not show greater levels of TAM or DDNP (P = .82). Conclusion In a mouse model of anaplastic thyroid cancer, ferumoxytol MRI showed 136% ± 88 greater uptake in orthotopic thyroid tumors compared with pulmonary lesions, which reflected high vascularization and greater tumor-associated macrophage (TAM) levels. Serine/threonine-protein kinase B-Raf inhibitor and anti-programmed death ligand 1 antibody elicited higher local TAM levels and 43% ± 20 greater therapeutic nanoparticle delivery but not higher vascularization in pulmonary tumors. © RSNA, 2020 Online supplemental material is available for this article. See also the editorial by Luker in this issue.

Efficient blockade of locally reciprocated tumor-macrophage signaling using a TAM-avid nanotherapy

Interpreting how multicellular interactions in the tumor affect resistance pathways to BRAF and MEK1/2 MAPK inhibitors (MAPKi) remains a challenge. To investigate this, we profiled global ligand-receptor interactions among tumor and stromal/immune cells from biopsies of MAPK-driven disease. MAPKi increased tumor-associated macrophages (TAMs) in some patients, which correlated with poor clinical response, and MAPKi coamplified bidirectional tumor-TAM signaling via receptor tyrosine kinases (RTKs) including AXL, MERTK, and their ligand GAS6. In xenograft tumors, intravital microscopy simultaneously monitored in situ single-cell activities of multiple kinases downstream of RTKs, revealing MAPKi increased TAMs and enhanced bypass signaling in TAM-proximal tumor cells. As a proof-of-principle strategy to block this signaling, we developed a multi-RTK kinase inhibitor nanoformulation that accumulated in TAMs and delayed disease progression. Thus, bypass signaling can reciprocally amplify across nearby cell types, offering new opportunities for therapeutic design.

A case report of primary anaplastic large cell lymphoma arising from the trachea

Anaplastic large cell lymphoma (ALCL) is an aggressive non-Hodgkin’s lymphoma. Its presentation as an isolated primary lesion in the airway is extremely rare and not often considered in the differential diagnosis of airway lesions. Thus, it is important to be aware of its presenting manifestations, imaging features and treatment complications. Here, we report a case of pathologically confirmed tracheal-based ALCL. We especially focus on presenting the salient imaging features of this entity and the associated clinical and pathological findings of this rare large airway disease.

Childbearing and Family Leave Policies for Resident Physicians at Top Training Institutions

This study describes childbearing and family leave at 15 graduate medical education (GME)–sponsoring institutions affiliated with 12 US medical schools on top 10 lists for funding or ranking.

Optimal acquisition and modeling parameters for accurate assessment of low Ktrans blood-brain barrier permeability using dynamic contrast-enhanced MRI

PURPOSE

To determine optimal parameters for acquisition and processing of dynamic contrast-enhanced MRI (DCE-MRI) to detect small changes in near normal low blood-brain barrier (BBB) permeability.

METHODS

Using a contrast-to-noise ratio metric (K-CNR) for Ktrans precision and accuracy, the effects of kinetic model selection, scan duration, temporal resolution, signal drift, and length of baseline on the estimation of low permeability values was evaluated with simulations.

RESULTS

The Patlak model was shown to give the highest K-CNR at low Ktrans . The Ktrans transition point, above which other models yielded superior results, was highly dependent on scan duration and tissue extravascular extracellular volume fraction (ve ). The highest K-CNR for low Ktrans was obtained when Patlak model analysis was combined with long scan times (10-30 min), modest temporal resolution (<60 s/image), and long baseline scans (1-4 min). Signal drift as low as 3% was shown to affect the accuracy of Ktrans estimation with Patlak analysis.

CONCLUSION

DCE acquisition and modeling parameters are interdependent and should be optimized together for the tissue being imaged. Appropriately optimized protocols can detect even the subtlest changes in BBB integrity and may be used to probe the earliest changes in neurodegenerative diseases such as Alzheimer's disease and multiple sclerosis.

ROCKETSHIP: a flexible and modular software tool for the planning, processing and analysis of dynamic MRI studies

BACKGROUND

Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) is a promising technique to characterize pathology and evaluate treatment response. However, analysis of DCE-MRI data is complex and benefits from concurrent analysis of multiple kinetic models and parameters. Few software tools are currently available that specifically focuses on DCE-MRI analysis with multiple kinetic models. Here, we developed ROCKETSHIP, an open-source, flexible and modular software for DCE-MRI analysis. ROCKETSHIP incorporates analyses with multiple kinetic models, including data-driven nested model analysis.

RESULTS

ROCKETSHIP was implemented using the MATLAB programming language. Robustness of the software to provide reliable fits using multiple kinetic models is demonstrated using simulated data. Simulations also demonstrate the utility of the data-driven nested model analysis. Applicability of ROCKETSHIP for both preclinical and clinical studies is shown using DCE-MRI studies of the human brain and a murine tumor model.

CONCLUSION

A DCE-MRI software suite was implemented and tested using simulations. Its applicability to both preclinical and clinical datasets is shown. ROCKETSHIP was designed to be easily accessible for the beginner, but flexible enough for changes or additions to be made by the advanced user as well. The availability of a flexible analysis tool will aid future studies using DCE-MRI. A public release of ROCKETSHIP is available at https://github.com/petmri/ROCKETSHIP .

Massive pancreatic pseudocyst with portal vein fistula: case report and proposed treatment algorithm

Pancreatic pseudocyst is a relatively common occurrence resulting from acute or chronic pancreatitis. However, a rare subset of these patients present with a pseudocyst fistulizing into the portal vein. We present the case of a 58 year-old woman with a rapidly expanding pancreatic pseudocyst with portal venous fistulization causing portal vein thrombosis, in addition to biliary and duodenal obstruction. The patient underwent surgical decompression with a cyst-gastrostomy and was well until one week post-operatively when she experienced massive gastrointestinal hemorrhage leading to her death. A review of the literature is presented and a treatment algorithm to manage patients with pancreatic pseudocyst to portal vein fistula is proposed.

Serial diffusion MRI to monitor and model treatment response of the targeted nanotherapy CRLX101

PURPOSE

Targeted nanotherapies are being developed to improve tumor drug delivery and enhance therapeutic response. Techniques that can predict response will facilitate clinical translation and may help define optimal treatment strategies. We evaluated the efficacy of diffusion-weighted magnetic resonance imaging to monitor early response to CRLX101 (a cyclodextrin-based polymer particle containing the DNA topoisomerase I inhibitor camptothecin) nanotherapy (formerly IT-101), and explored its potential as a therapeutic response predictor using a mechanistic model of tumor cell proliferation.

EXPERIMENTAL DESIGN

Diffusion MRI was serially conducted following CRLX101 administration in a mouse lymphoma model. Apparent diffusion coefficients (ADCs) extracted from the data were used as treatment response biomarkers. Animals treated with irinotecan (CPT-11) and saline were imaged for comparison. ADC data were also input into a mathematical model of tumor growth. Histological analysis using cleaved-caspase 3, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling, Ki-67, and hematoxylin and eosin (H&E) were conducted on tumor samples for correlation with imaging results.

RESULTS

CRLX101-treated tumors at day 2, 4, and 7 posttreatment exhibited changes in mean ADC = 16 ± 9%, 24 ± 10%, 49 ± 17%, and size (TV) = -5 ± 3%, -30 ± 4%, and -45 ± 13%, respectively. Both parameters were statistically greater than controls [p(ADC) ≤ 0.02, and p(TV) ≤ 0.01 at day 4 and 7], and noticeably greater than CPT-11-treated tumors (ADC = 5 ± 5%, 14 ± 7%, and 18 ± 6%; TV = -15 ± 5%, -22 ± 13%, and -26 ± 8%). Model-derived parameters for cell proliferation obtained using ADC data distinguished CRLX101-treated tumors from controls (P = 0.02).

CONCLUSIONS

Temporal changes in ADC specified early CRLX101 treatment response and could be used to model image-derived cell proliferation rates following treatment. Comparisons of targeted and nontargeted treatments highlight the utility of noninvasive imaging and modeling to evaluate, monitor, and predict responses to targeted nanotherapeutics.

Quantitative, simultaneous PET/MRI for intratumoral imaging with an MRI-compatible PET scanner

Noninvasive methods are needed to explore the heterogeneous tumor microenvironment and its modulation by therapy. Hybrid PET/MRI systems are being developed for small-animal and clinical use. The advantage of these integrated systems depends on their ability to provide MR images that are spatially coincident with simultaneously acquired PET images, allowing combined functional MRI and PET studies of intratissue heterogeneity. Although much effort has been devoted to developing this new technology, the issue of quantitative and spatial fidelity of PET images from hybrid PET/MRI systems to the tissues imaged has received little attention. Here, we evaluated the ability of a first-generation, small-animal MRI-compatible PET scanner to accurately depict heterogeneous patterns of radiotracer uptake in tumors.

METHODS

Quantitative imaging characteristics of the MRI-compatible PET (PET/MRI) scanner were evaluated with phantoms using calibration coefficients derived from a mouse-sized linearity phantom. PET performance was compared with a commercial small-animal PET system and autoradiography in tumor-bearing mice. Pixel and structure-based similarity metrics were used to evaluate image concordance among modalities. Feasibility of simultaneous PET/MRI functional imaging of tumors was explored by following (64)Cu-labeled antibody uptake in relation to diffusion MRI using cooccurrence matrix analysis.

RESULTS

The PET/MRI scanner showed stable and linear response. Activity concentration recovery values (measured and true activity concentration) calculated for 4-mm-diameter rods within linearity and uniform activity rod phantoms were near unity (0.97 ± 0.06 and 1.03 ± 0.03, respectively). Intratumoral uptake patterns for both (18)F-FDG and a (64)Cu-antibody acquired using the PET/MRI scanner and small-animal PET were highly correlated with autoradiography (r > 0.99) and with each other (r = 0.97 ± 0.01). On the basis of these data, we performed a preliminary study comparing diffusion MRI and radiolabeled antibody uptake patterns over time and visualized movement of antibodies from the vascular space into the tumor mass.

CONCLUSION

The MRI-compatible PET scanner provided tumor images that were quantitatively accurate and spatially concordant with autoradiography and the small-animal PET examination. Cooccurrence matrix approaches enabled effective analysis of multimodal image sets. These observations confirm the ability of the current simultaneous PET/MRI system to provide accurate observations of intratumoral function and serve as a benchmark for future evaluations of hybrid instrumentation.

Receptor-targeted iron oxide nanoparticles for molecular MR imaging of inflamed atherosclerotic plaques

In a number of literature reports iron oxide nanoparticles have been investigated for use in imaging atherosclerotic plaques and found to accumulate in plaques via uptake by macrophages, which are critical in the process of atheroma initiation, propagation, and rupture. However, the uptake of these agents is non-specific; thus the labeling efficiency for plaques in vivo is not ideal. We have developed targeted agents to improve the efficiency for labeling macrophage-laden plaques. These probes are based on iron oxide nanoparticles coated with dextran sulfate, a ligand of macrophage scavenger receptor type A (SR-A). We have sulfated dextran-coated iron oxide nanoparticles (DIO) with sulfur trioxide, thereby targeting our nanoparticle imaging agents to SR-A. The sulfated DIO (SDIO) remained mono-dispersed and had an average hydrodynamic diameter of 62 nm, an r(1) relaxivity of 18.1 mM(-1) s(-1), and an r(2) relaxivity of 95.8 mM(-1) s(-1) (37 °C, 1.4 T). Cell studies confirmed that these nanoparticles were nontoxic and specifically targeted to macrophages. In vivo MRI after intravenous injection of the contrast agent into an atherosclerotic mouse injury model showed substantial signal loss on the injured carotid at 4 and 24 h post-injection of SDIO. No discernable signal decrease was seen at the control carotid and only mild signal loss was observed for the injured carotid post-injection of non-sulfated DIO, indicating preferential uptake of the SDIO particles at the site of atherosclerotic plaque. These results indicate that SDIO can facilitate MRI detection and diagnosis of vulnerable plaques in atherosclerosis.

A robust coregistration method for in vivo studies using a first generation simultaneous PET/MR scanner

PURPOSE

Hybrid positron emission tomography (PET)/magnetic resonance (MR) imaging systems have recently been built that allow functional and anatomical information obtained from PET and MR to be acquired simultaneously. The authors have developed a robust coregistration scheme for a first generation small animal PET/MR imaging system and illustrated the potential of this system to study intratumoral heterogeneity in a mouse model.

METHODS

An alignment strategy to fuse simultaneously acquired PET and MR data, using the MR imaging gradient coordinate system as the reference basis, was developed. The fidelity of the alignment was evaluated over multiple study sessions. In order to explore its robustness in vivo, the alignment strategy was applied to explore the heterogeneity of glucose metabolism in a xenograft tumor model, using 18F-FDG-PET to guide the acquisition of localized 1H MR spectra within a single imaging session.

RESULTS

The alignment method consistently fused the PET/MR data sets with subvoxel accuracy (registration error mean = 0.55 voxels, < 0.28 mm); this was independent of location within the field of view. When the system was used to study intratumoral heterogeneity within xenograft tumors, a correlation of high 18F-FDG-PET signal with high choline/creatine ratio was observed.

CONCLUSIONS

The authors present an implementation of an efficient and robust coregistration scheme for multimodal noninvasive imaging using PET and MR. This setup allows time-sensitive, multimodal studies of physiology to be conducted in an efficient manner.

A study of the timing properties of position-sensitive avalanche photodiodes

In this paper, we study position-dependent timing shifts and timing resolution in position sensitive avalanche photodiodes (PSAPDs) and their effects on the coincidence window used in positron emission tomography (PET) systems using these devices. There is a delay in PSAPD signals that increases as the excitation position moves from the corner to the center of the device and the timing resolution concurrently worsens. The difference in timing between the center and the corner can be up to 30.7 ns for a 14 x 14 mm(2) area PSAPD. This means that a PSAPD-based PET system could require a very wide coincidence timing window (>60 ns) if this effect is not corrected, although the individual crystal pairs still have full-width half-maximum (FWHM) timing resolutions better than 7.4 ns. In addition to characterizing the timing properties of PSAPDs, two correction methods were developed and applied to data from a pair of PSAPD detectors. These two timing offset corrections reduced the timing shift of a crystal pair from 52.4 ns to 9.7 ns or 1.3 ns, improved the FWHM timing resolution of the detector pair from 24.6 ns to 9.5 ns or 6.0 ns and reduced the timing window (sufficient to cover at least twice the FWHM for all crystal pairs) from 65.1 ns to 22.0 ns or 15.2 ns, respectively. A two-step timing alignment method is proposed for a PET system consisting of multiple PSAPDs. Lastly, the effect of PSAPD size on the timing performance was also evaluated.