RSS 1.0Radiology
ABOUT THIS COMMUNITY
The mission of the Department of Radiology at UMass Chan Medical School is to bring scientific advances in medical imaging to clinical application.
Collections in this community
-
Luna Lab [55]
-
Padrón-Craig Lab [71]
-
Radiology Publications [1137]
-
Witman Lab [125]
Recently Published
-
Prospective study on embolization of intracranial aneurysms with the pipeline device (PREMIER study): 3-year results with the application of a flow diverter specific occlusion classificationBACKGROUND: The pipeline embolization device (PED; Medtronic) has presented as a safe and efficacious treatment for small- and medium-sized intracranial aneurysms. Independently adjudicated long-term results of the device in treating these lesions are still indeterminate. We present 3-year results, with additional application of a flow diverter specific occlusion scale. METHODS: PREMIER (prospective study on embolization of intracranial aneurysms with pipeline embolization device) is a prospective, single-arm trial. Inclusion criteria were patients with unruptured wide-necked intracranial aneurysms < /=12 mm. Primary effectiveness (complete aneurysm occlusion) and safety (major neurologic event) endpoints were independently monitored and adjudicated. RESULTS: As per the protocol, of 141 patients treated with a PED, 25 (17.7%) required angiographic follow-up after the first year due to incomplete aneurysm occlusion. According to the Core Radiology Laboratory review, three (12%) of these patients progressed to complete occlusion, with an overall rate of complete aneurysm occlusion at 3 years of 83.3% (115/138). Further angiographic evaluation using the modified Cekirge-Saatci classification demonstrated that complete occlusion, neck residual, or aneurysm size reduction occurred in 97.1%. The overall combined safety endpoint at 3 years was 2.8% (4/141), with only one non-debilitating major event occurring after the first year. There was one case of aneurysm recurrence but no cases of delayed rupture in this series. CONCLUSIONS: The PED device presents as a safe and effective modality in treating small- and medium-sized intracranial aneurysms. The application of a flow diverter specific occlusion classification attested the long-term durability with higher rate of successful aneurysm occlusion and no documented aneurysm rupture. TRIAL REGISTRATION: NCT02186561.
-
Chronic Wound Image Augmentation and Assessment Using Semi-Supervised Progressive Multi-Granularity EfficientNetGoal: Augment a small, imbalanced, wound dataset by using semi-supervised learning with a secondary dataset. Then utilize the augmented wound dataset for deep learning-based wound assessment. Methods: The clinically-validated Photographic Wound Assessment Tool (PWAT) scores eight wound attributes: Size, Depth, Necrotic Tissue Type, Necrotic Tissue Amount, Granulation Tissue type, Granulation Tissue Amount, Edges, Periulcer Skin Viability to comprehensively assess chronic wound images. A small corpus of 1639 wound images labeled with ground truth PWAT scores was used as reference. A Semi-Supervised learning and Progressive Multi-Granularity training mechanism were used to leverage a secondary corpus of 9870 unlabeled wound images. Wound scoring utilized the EfficientNet Convolutional Neural Network on the augmented wound corpus. Results: Our proposed Semi-Supervised PMG EfficientNet (SS-PMG-EfficientNet) approach estimated all 8 PWAT sub-scores with classification accuracies and F1 scores of about 90% on average, and outperformed a comprehensive list of baseline models and had a 7% improvement over the prior state-of-the-art (without data augmentation). We also demonstrate that synthetic wound image generation using Generative Adversarial Networks (GANs) did not improve wound assessment. Conclusions: Semi-supervised learning on unlabeled wound images in a secondary dataset achieved impressive performance for deep learning-based wound grading.
-
Mesh modeling of system geometry and anatomy phantoms for realistic GATE simulations and their inclusion in SPECT reconstructionObjective: Monte-Carlo simulation studies have been essential for advancing various developments in SPECT imaging, such as system design and accurate image reconstruction. Among the simulation software available, GATE is one of the most used simulation toolkits in nuclear medicine, which allows building systems and attenuation phantom geometries based on the combination of idealized volumes. However, these idealized volumes are inadequate for modeling free-form shape components of such geometries. Recent GATE versions alleviate these major limitations by allowing users to import triangulated surface meshes. Approach: In this study, we describe our mesh-based simulations of a next-generation multi-pinhole SPECT system dedicated to clinical brain imaging, called AdaptiSPECT-C. To simulate realistic imaging data, we incorporated in our simulation the XCAT phantom, which provides an advanced anatomical description of the human body. An additional challenge with the AdaptiSPECT-C geometry is that the default voxelized XCAT attenuation phantom was not usable in our simulation due to intersection of objects of dissimilar materials caused by overlap of the air containing regions of the XCAT beyond the surface of the phantom and the components of the imaging system. Main results: We validated our mesh-based modeling against the one constructed by idealized volumes for a simplified single vertex configuration of AdaptiSPECT-C through simulated projection data of 123I-activity distributions. We resolved the overlap conflict by creating and incorporating a mesh-based attenuation phantom following a volume hierarchy. We then evaluated our reconstructions with attenuation and scatter correction for projections obtained from simulation consisting of mesh-based modeling of the system and the attenuation phantom for brain imaging. Our approach demonstrated similar performance as the reference scheme simulated in air for uniform and clinical-like 123I-IMP brain perfusion source distributions. Significance: This work enables the simulation of complex SPECT acquisitions and reconstructions for emulating realistic imaging data close to those of actual patients.
-
Changes in Stage at Presentation among Lung and Breast Cancer Patients During the COVID-19 PandemicBackground: The COVID-19 pandemic altered access to healthcare by decreasing number of patients able to receive preventative care and cancer screening. We hypothesized that given these changes in access to care, radiologic screening for breast and lung cancer would be decreased, and patients with these cancers would consequently present at later stages of their disease. Design: Retrospective cross-sectional study of 2017-September 2021 UMass Memorial Tumor Registry for adult breast and lung cancer patients. Changes in stage at presentation of breast and lung cancer during the COVID-19 pandemic were measured, defined as prior to and during COVID-19. Results: There were no statistically significant changes in the overall stage of presentation before or during the COVID-19 pandemic for either breast or lung cancer patients. Analysis of case presentation and stage during periods of COVID-19 surges that occurred over the time of this study compared to pre-pandemic data demonstrated a statistically significant decrease in overall presentation of breast cancer patients in the first surge, with no other statistically significant changes in breast cancer presentation. A non-statistically significant decrease in lung cancer presentations was seen during the initial surge of COVID-19. There was also a statistically significant increase in early-stage presentation of lung cancer during the second and third COVID-19 surges. Conclusions: In the two years after the COVID-19 pandemic we were not able to demonstrate stage migration at presentation of breast and lung cancer patients to later stages despite decreases in overall presentation during the initial two years of the COVID pandemic. An increase in early-stage lung cancer during the second and third surges is interesting and could be related to increased chest imaging for COVID pneumonia.
-
Multiple expressions of "expert" abnormality gist in novices following perceptual learningWith a brief half-second presentation, a medical expert can determine at above chance levels whether a medical scan she sees is abnormal based on a first impression arising from an initial global image process, termed "gist." The nature of gist processing is debated but this debate stems from results in medical experts who have years of perceptual experience. The aim of the present study was to determine if gist processing for medical images occurs in naïve (non-medically trained) participants who received a brief perceptual training and to tease apart the nature of that gist signal. We trained 20 naïve participants on a brief perceptual-adaptive training of histology images. After training, naïve observers were able to obtain abnormality detection and abnormality categorization above chance, from a brief 500 ms masked presentation of a histology image, hence showing "gist." The global signal demonstrated in perceptually trained naïve participants demonstrated multiple dissociable components, with some of these components relating to how rapidly naïve participants learned a normal template during perceptual learning. We suggest that multiple gist signals are present when experts view medical images derived from the tens of thousands of images that they are exposed to throughout their training and careers. We also suggest that a directed learning of a normal template may produce better abnormality detection and identification in radiologists and pathologists.
-
Current and upcoming radionuclide therapies in the direction of precision oncology: A narrative reviewAs new molecular tracers are identified to target specific receptors, tissue, and tumor types, opportunities arise for the development of both diagnostic tracers and their therapeutic counterparts, termed "theranostics." While diagnostic tracers utilize positron emitters or gamma-emitting radionuclides, their theranostic counterparts are typically bound to beta and alpha emitters, which can deliver specific and localized radiation to targets with minimal collateral damage to uninvolved surrounding structures. This is an exciting time in molecular imaging and therapy and a step towards personalized and precise medicine in which patients who were either without treatment options or not candidates for other therapies now have expanded options, with tangible data showing improved outcomes. This manuscript explores the current state of theranostics, providing background, treatment specifics, and toxicities, and discusses future potential trends.
-
Resident Perspective of the Virtual Diagnostic Radiology Residency Interview Process: A National Survey From the Association of Program Directors in RadiologyRationale and objectives: The purpose of this study was to assess differences in first-year radiology resident perception of the match process and early satisfaction with residency programs between those who matched in 2020 versus 2021, the first virtual application cycle after the start of the COVID-19 pandemic. Materials and methods: A 33-question survey was distributed to first-year diagnostic radiology residents at programs throughout the United States through the Association of Program Directors in Radiology. Responses were collected in June of 2022 from residents who matched in 2020 and in July of 2022 from residents who matched in 2021. Questions were designed to assess applicant demographics, outcomes and attitudes towards the interview process. Comparison was made between the two cohorts. Results: Of the 2231 matched residents in the 2020 and 2021 match years, 108 residents (4.8%) received, responded, and met inclusion criteria for the survey. Forty-three of 46 (92.5%) respondents that matched in 2020 interviewed in-person compared to one of 60 (1.7%) that matched in 2021 (p < 0.0001). There was no difference in satisfaction of match results, current training programs, work culture, satisfaction with facilities, and depiction of residency structure. Applicants from the 2021 cohort were more likely to express concerns about interview hoarding, having enough time to ask questions on interview days, and ability to accurately present themselves in interviews but were more likely to favor virtual interviews for future cycles. Conclusion: The virtual interview process is perceived neutrally or positively by most early diagnostic radiology residents and produced similar satisfactory results compared to applicants that interviewed in person. Attention should be given to concerns of those who matched virtually if the virtual interview process is to be continued.
-
Tet-Regulated Expression and Optical Clearing for In Vivo Visualization of Genetically Encoded Chimeric dCas9/Fluorescent Protein ProbesThe catalytically inactive mutant of Cas9 (dCas9) endonuclease has multiple biomedical applications, with the most useful being the activation/repression of transcription. dCas9 family members are also emerging as potential experimental tools for gene mapping at the level of individual live cells and intact tissue. We performed initial testing on a set of tools for Cas9-mediated visualization of nuclear compartments. We investigated doxycycline (Dox)-inducible (Tet-On) intracellular distribution of constructs encoding dCas9 orthologs from St. thermophilus (St) and N. meningitides (Nm) fused with EGFP and mCherry fluorescent proteins (FP) in human A549 cells. We also studied time-dependent expression of these chimeric fluorescent constructs (dCas9-FP) after Tet-On induction in live cells and compared it with the time course of dCas9-FP expression in experimental dCas9-FP-expressing tumor xenografts using a combination of fluorescence imaging and in vivo contrast-assisted magnetic resonance imaging for assessing the extent of tumor perfusion. In vivo Dox-induction of mCherry-chimera expression occurred in tumor xenografts as early as 24 h post-induction and was visualized by using optical clearing (OC) of the skin. OC via topical application of gadobutrol enabled high-contrast imaging of FP expression in tumor xenografts due to a 1.1-1.2-fold increase in FI in both the red and green channels.
-
Glb1 knockout mouse model shares natural history with type II GM1 gangliosidosis patientsGM1 gangliosidosis is a rare lysosomal storage disorder affecting multiple organ systems, primarily the central nervous system, and is caused by functional deficiency of β-galactosidase (GLB1). Using CRISPR/Cas9 genome editing, we generated a mouse model to evaluate characteristics of the disease in comparison to GM1 gangliosidosis patients. Our Glb1-/- mice contain small deletions in exons 2 and 6, producing a null allele. Longevity is approximately 50 weeks and studies demonstrated that female Glb1-/- mice die six weeks earlier than male Glb1-/- mice. Gait analyses showed progressive abnormalities including abnormal foot placement, decreased stride length and increased stance width, comparable with what is observed in type II GM1 gangliosidosis patients. Furthermore, Glb1-/- mice show loss of motor skills by 20 weeks assessed by adhesive dot, hanging wire, and inverted grid tests, and deterioration of motor coordination by 32 weeks of age when evaluated by rotarod testing. Brain MRI showed progressive cerebellar atrophy in Glb1-/- mice as seen in some patients. In addition, Glb1-/- mice also show significantly increased levels of a novel pentasaccharide biomarker in urine and plasma which we also observed in GM1 gangliosidosis patients. Glb1-/- mice also exhibit accumulation of glycosphingolipids in the brain with increases in GM1 and GA1 beginning by 8 weeks. Surprisingly, despite being a null variant, this Glb1-/- mouse most closely models the less severe type II disease and will guide the development of new therapies for patients with the disorder.
-
Preclinical model of anterior circulation intracranial stentingBackground: Preclinical testing of intracranial stents is currently performed in the peripheral circulation, and rarely in the basilar artery of the dog. Objective: To test the feasibility of intracranial stenting in the middle cerebral artery (MCA) of the dog and explore the use of MRI to detect thromboembolic complications. Methods: Six purpose-bred cross-hound dogs were used for proof-of-concept stenting of both MCAs in each animal. Immediately following the procedure, the animals were imaged with MRI. MRI was repeated weekly for 1 month. After the final angiography at 30 days, the animals were euthanized for pathological assessment of the stents and the brain. Results: We successfully deployed 12 stents in the MCAs of all animals. We deployed three techniques for microcatheterization of the MCA-namely, directly through the internal carotid artery (ICA), using anastomotic arteries from the external carotid artery, or via the contralateral ICA through the anterior communicating artery. Two iatrogenic perforations of the ICA with formation of an arteriovenous fistula occurred, without clinical sequelae, which spontaneously resolved on follow-up. All animals tolerated the procedure and completed the follow-up surveillance. MRI revealed procedural thromboembolic induced areas of restricted diffusion, and only one instance of a delayed thromboembolic lesion during surveillance. At follow-up angiography, the devices were all patent. Conclusion: We describe a new preclinical model of intracranial stenting in the MCA. Such a model may prove useful for evaluating new surface modifications.
-
Balloon protection of the vein of Labbé during embolisation of a dural arteriovenous fistulaWe describe a novel technique of vein of Labbé preservation using balloon protection during embolisation of a transverse-sigmoid sinus dural arteriovenous fistula. A patient with refractory Cognard type IV fistula of the left transverse-sigmoid sinus and persistent pulsatile tinnitus underwent successful embolisation of the lesion via transarterial route. During embolisation, a dual lumen balloon was simultaneously inflated within the vein of Labbé, at its orifice in the transverse-sigmoid sinus junction, to prevent embolic reflux. This allowed for liquid embolic embolisation of the fistula via the transarterial route resulting in complete occlusion. The patient recovered well with marked improvement of his tinnitus.
-
Audit of Prior Screening Mammograms of Screen-Detected Cancers: Implications for the Delay in Breast Cancer DetectionWhen cancer is detected in a screening mammogram, on occasion retrospective review of prior screening (pre-index) mammograms indicates a likely presence of cancer. These missed cancers during pre-index screens constitute a delay in detection and diagnosis. This study was undertaken to quantify the missed cancer rate by auditing pre-index screens to improve the quality of mammography screening practice. From a cohort of 135 screen-detected cancers, 120 pre-index screening mammograms could be retrieved and served as the study sample. A consensus read by 2 radiologists who interpreted the pre-index screens in an unblinded manner with full knowledge of cancer location, cancer type, lesion type, and pathology served as the truth or reference standard. Five radiologists interpreted the pre-index screens in a blinded manner. Established performance metrics such as sensitivity and specificity were quantified for each reader in interpreting these pre-index screens in a blinded manner. All five radiologists detected lesions in 8/120 (6.7%) screens. Excluding the 2 readers whose performance was close to random, all the 3 remaining readers detected lesions in 13 pre-index screens. This indicates that there is a delay in diagnosis by at least one cycle from 8/120 (6.7%) to 13/120 (10.8%). There were no observable trends in terms of either the cancer type or the lesion type. Auditing prior screening mammograms in screen-detected cancers can help in identifying the proportion of cases that were missed during interpretation and help in quantifying the delay in breast cancer detection.
-
Artificial Intelligence in Breast X-Ray ImagingThis topical review is focused on the clinical breast x-ray imaging applications of the rapidly evolving field of artificial intelligence (AI). The range of AI applications is broad. AI can be used for breast cancer risk estimation that could allow for tailoring the screening interval and the protocol that are woman-specific and for triaging the screening exams. It also can serve as a tool to aid in the detection and diagnosis for improved sensitivity and specificity and as a tool to reduce radiologists' reading time. AI can also serve as a potential second 'reader' during screening interpretation. During the last decade, numerous studies have shown the potential of AI-assisted interpretation of mammography and to a lesser extent digital breast tomosynthesis; however, most of these studies are retrospective in nature. There is a need for prospective clinical studies to evaluate these technologies to better understand their real-world efficacy. Further, there are ethical, medicolegal, and liability concerns that need to be considered prior to the routine use of AI in the breast imaging clinic.
-
Letter From the Guest EditorsIt has been a privilege to serve as Guest Editors for this issue of Seminars. We are extremely thankful to Dr. Howard Raymond for the invitation. The field of breast imaging has adapted to new innovations, technologies, cyberthreats and issues related to diversity, equity and inclusion. When planning this breast imaging focused issue, we aimed to not only include chapters on recent technological advances, but also chapters that discuss relevant practical issues that would benefit our readers. We have tried our best to integrate exciting new innovations with subjects of contemporary interest.
-
The Exceedingly Rapid Development of an Intracranial AneurysmDespite significant diagnostic and technical progress in managing intracranial aneurysms, there are still open questions in understanding their pathophysiology: how fast can they form and grow? We had the chance to observe the "de novo" genesis and rupture of an aneurysm of a left MCA posterior trunk M3 branch within 14 days in one of our patients. We were in the position to compare an initially inconspicuous vessel, assessed during a diagnostic cerebral angiogram with 3D acquisitions, performed as an elective follow-up to monitor the decade stability of a transitional aneurysm in the same vascular territory, and the same vessel only two weeks after, harboring a new small ruptured aneurysm. Several studies along the intracranial aneurysms' pathophysiology have been reported but primarily oriented toward identifying uncommon conditions such as inherent defects in collagen synthesis, genetic or familial factors, or basic anatomic variations or abnormalities in the cerebral vasculature. Suppose this case report does not pretend to provide a clear answer to these questions. However, it is up to date, the shortest time (14 days) reported in the literature for a well-documented "de novo" genesis and rupture of an intracranial aneurysm "in vivo" in humans. The purpose of this case report is not only to underscore the unpredictability of this vascular disease but, even more, to support the idea that further investigation, with more modern methodologies, is of paramount importance in determining the etiopathogenesis and behavior of this stealthy disease.
-
Brain Alterations in Aged OVT73 Sheep Model of Huntington's Disease: An MRI Based ApproachBackground: Huntington's disease (HD) is a fatal neurodegenerative autosomal dominant disorder with prevalence of 1 : 20000 that has no effective treatment to date. Translatability of candidate therapeutics could be enhanced by additional testing in large animal models because of similarities in brain anatomy, size, and immunophysiology. These features enable realistic pre-clinical studies of biodistribution, efficacy, and toxicity. Objective and methods: Here we non-invasively characterized alterations in brain white matter microstructure, neurochemistry, neurological status, and mutant Huntingtin protein (mHTT) levels in cerebrospinal fluid (CSF) of aged OVT73 HD sheep. Results: Similar to HD patients, CSF mHTT differentiates HD from normal sheep. Our results are indicative of a decline in neurological status, and alterations in brain white matter diffusion and spectroscopy metric that are more severe in aged female HD sheep. Longitudinal analysis of aged female HD sheep suggests that the decline is detectable over the course of a year. In line with reports of HD human studies, white matter alterations in corpus callosum correlates with a decline in gait of HD sheep. Moreover, alterations in the occipital cortex white matter correlates with a decline in clinical rating score. In addition, the marker of energy metabolism in striatum of aged HD sheep, shows a correlation with decline of clinical rating score and eye coordination. Conclusion: This data suggests that OVT73 HD sheep can serve as a pre-manifest large animal model of HD providing a platform for pre-clinical testing of HD therapeutics and non-invasive tracking of the efficacy of the therapy.
-
Direct in situ protein tagging in Chlamydomonas reinhardtii utilizing TIM, a method for CRISPR/Cas9-based targeted insertional mutagenesisChlamydomonas reinhardtii is an important model organism for the study of many cellular processes, and protein tagging is an increasingly indispensable tool for these studies. To circumvent the disadvantages of conventional approaches in creating a tagged cell line, which involve transforming either a wild-type or null-mutant cell line with an exogenous DNA construct that inserts randomly into the genome, we developed a strategy to tag the endogenous gene in situ. The strategy utilizes TIM, a CRISPR/Cas9-based method for targeted insertional mutagenesis in C. reinhardtii. We have tested the strategy on two genes: LF5/CDKL5, lack of which causes a long-flagella phenotype, and Cre09.g416350/NAP1L1, which has not been studied previously in C. reinhardtii. We successfully tagged the C-terminus of wild-type LF5 with the hemagglutinin (HA) tag with an efficiency of 7.4%. Sequencing confirmed that these strains are correctly edited. Western blotting confirmed the expression of HA-tagged LF5, and immunofluorescence microscopy showed that LF5-HA is localized normally. These strains have normal length flagella and appear wild type. We successfully tagged the N-terminus of Cre09.g416350 with mNeonGreen-3xFLAG with an efficiency of 9%. Sequencing showed that the tag region in these strains is as expected. Western blotting confirmed the expression of tagged protein of the expected size in these strains, which appeared to have normal cell size, growth rate, and swimming speed. This is the first time that C. reinhardtii endogenous genes have been edited in situ to express a wild-type tagged protein. This effective, efficient, and convenient TIM-tagging strategy promises to be a useful tool for the study of nuclear genes, including essential genes, in C. reinhardtii.
-
Operationalizing the New ABR Residency Leave Policy for Trainees: A Practical Guide for Program DirectorsINTRODUCTION In 2021, the American Board of Radiology (ABR) announced a new residency leave policy which provided much needed guidelines for leave during residency for both trainees and program directors (PDs) (1). The policy went into effect for the 2021-2022 academic year and allows for a maximum leave “that does not exceed an average of eight weeks (40 working days) per academic year over the duration of the residency.” While PDs were eager to have guidance and a new trainee-friendly policy, many did not know where to start with implementing the policy and how it would affect scheduling. This manuscript provides guidance for operationalizing the new ABR Residency Leave Policy so that it is optimal for trainees, programs and PDs.
-
Rate of periprocedural stroke in diagnostic cerebral angiograms comparing transradial versus transfemoral accessPurpose: Transradial access for neurointerventional procedures has increased in popularity over the past few years due to data from extrapolated interventional cardiology studies, patient preference, and early reports of feasibility using this approach. Our aim was to evaluate the incidence of periprocedural stroke in patients undergoing transradial versus transfemoral access for diagnostic cerebral angiograms. Methods: We retrospectively reviewed our neurointerventional database and identified all patients who underwent a diagnostic angiogram between May 2019 and July 2021. Patients were further divided into transradial versus transfemoral access. In patients with postprocedural stroke, symptoms and National Institute of Health Stroke Scale score were recorded. Pertinent laboratory values and procedural data was reviewed, including COVID status, platelet count, International normalized ratio (INR), Glomerular filtration rate (GFR), vessels catheterized, amount of contrast used, and fluoroscopy time. Imaging work-up for stroke symptoms was reviewed, if available. Results: Thousand two-hundred thirty eight diagnostic cerebral angiograms with 656 patients (53%) undergoing transradial access. Stroke symptoms after angiogram were only observed in the transradial group (5 patients; 0.4% total and 0.8% among radial access cases, respectively). Symptoms included word finding difficulty, paresthesia, or weakness. Three patients underwent cross-sectional imaging, computed tomography was negative in all three patients. Magnetic resonance imaging showed small, scattered infarcts in two patients. All symptoms resolved without additional hospitalization. Conclusion: In our experience, using transradial access for diagnostic cerebral angiograms was associated with a low but not negligible incidence of periprocedural strokes. Patient anatomy should be evaluated prior to selection of vascular access. Patients should be made aware of a slightly higher periprocedural stroke risk with transradial access.
-
Dilated cardiomyopathy mutation E525K in human beta-cardiac myosin stabilizes the interacting-heads motif and super-relaxed state of myosinThe auto-inhibited, super-relaxed (SRX) state of cardiac myosin is thought to be crucial for regulating contraction, relaxation, and energy conservation in the heart. We used single ATP turnover experiments to demonstrate that a dilated cardiomyopathy (DCM) mutation (E525K) in human beta-cardiac myosin increases the fraction of myosin heads in the SRX state (with slow ATP turnover), especially in physiological ionic strength conditions. We also utilized FRET between a C-terminal GFP tag on the myosin tail and Cy3ATP bound to the active site of the motor domain to estimate the fraction of heads in the closed, interacting-heads motif (IHM); we found a strong correlation between the IHM and SRX state. Negative stain electron microscopy and 2D class averaging of the construct demonstrated that the E525K mutation increased the fraction of molecules adopting the IHM. Overall, our results demonstrate that the E525K DCM mutation may reduce muscle force and power by stabilizing the auto-inhibited SRX state. Our studies also provide direct evidence for a correlation between the SRX biochemical state and the IHM structural state in cardiac muscle myosin. Furthermore, the E525 residue may be implicated in crucial electrostatic interactions that modulate this conserved, auto-inhibited conformation of myosin.
