Although tube current modulation (TCM) is routinely implemented in modern computed tomography (CT) scans, no existing CT simulator is capable of generating realistic images with TCM. The goal of this study was to develop such a framework to (1) facilitate patient-specific optimization of TCM parameters and (2) enable future virtual imaging trials (VITs) with more clinically realistic image quality and x-ray flux distributions. The framework was created by developing a TCM module and integrating it with an existing CT simulator (DukeSim). The developed module utilizes scanner-calibrated TCM parameters and two localizer radiographs to compute the mAs for each simulated CT projection. This simulation pipeline was validated in two parts. First, DukeSim was validated in the context of a commercial scanner with TCM (SOMATOM Force, Siemens Healthineers) by imaging a physical CT phantom (Mercury, Sun Nuclear) and its computational analogue. Second, the TCM module was validated by imaging a computational anthropomorphic phantom (ATOM, CIRS) using DukeSim with real and module generated TCM profiles. The validation demonstrated DukeSim's realism in terms of noise magnitude, noise texture, spatial resolution, and image contrast (with average differences of 0.38%, 6.31%, 0.43%, and −9 HU, respectively). It also demonstrated the TCM module's realism in terms of projection-level mAs and resulting noise magnitude (2.86% and −2.60%, respectively). Finally, the framework was applied to a pilot VIT simulating images of three computational anthropomorphic phantoms (XCAT, with body mass indices (BMIs) of 24.3, 28.2, and 33.0) under five different TCM settings. The optimal TCM for each phantom was characterized based on various criteria, such as minimizing mAs or maximizing image quality. 'Very Weak' TCM minimized noise for the 24.3 BMI phantom, while 'Very Strong' TCM minimized noise for the
Heller myotomy is the “gold-standard” therapy for achalasia, alleviating symptoms by defunctionalizing the lower esophageal sphincter mechanism. Observation has suggested many differences between young and old patients with achalasia, raising the question: is achalasia in younger patients a different disorder than it is in older patients? This study was undertaken to answer this question. With Institutional Review Board approval, 648 patients undergoing laparoscopic Heller myotomy from 1992–2016 were prospectively followed up. Patients self-assessed symptom frequency/severity preoperatively and postoperatively using a Likert scale; 0 (never/not bothersome) to 10 (always/very bothersome). Before myotomy, frequency/severity of many symptoms (e.g., “dysphagia,” “chest pain,” and “regurgitation”) inversely correlated with age (P < 0.01 each). Symptom duration and the number of previous abdominal operations correlated with age, as did intraoperative complications (e.g., gastrotomy), postoperative complications (e.g., atrial fibrillation), and length of stay (P < 0.01 for each). Patients experienced amelioration of all symptoms queried, regardless of age (P < 0.01 each). Age did affect outcome because older patients had less frequent and severe symptoms. Age did not affect improvement of symptoms (e.g., dysphagia) (i.e., differences between preoperative and postoperative scores) (P = 0.88). Age did not influence symptom resolution or patient satisfaction (P = 0.98 and P = 0.15, respectively). The presentation with achalasia, hospital course, and outcome after myotomy are significantly impacted by age, whereas patient improvement after myotomy is constant independent of age. Younger and older patients have different presentations, experiences, and outcomes; these patients seem to have “different disorders”, but Heller myotomy provides similar significant amelioration of symptoms independent of age.
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