Dual-energy computed tomography imaging with megavoltage and kilovoltage X-ray spectra.

Purpose: Single-energy computed tomography (CT) often suffers from poor contrast yet remains critical for effective radiotherapy treatment. Modern therapy systems are often equipped with both megavoltage (MV) and kilovoltage (kV) X-ray sources and thus already possess hardware for dual-energy (DE) CT. There is unexplored potential for enhanced image contrast using MV-kV DE-CT in radiotherapy contexts. Approach: A single-line integral toy model was designed for computing basis material signal-to-noise ratio (SNR) using estimation theory. Five dose-matched spectra (3 kV, 2 MV) and three variables were considered: spectral combination, spectral dose allocation, and object material composition. The single-line model was extended to a simulated CT acquisition of an anthropomorphic phantom with and without a metal implant. Basis material sinograms were computed and synthesized into virtual monoenergetic images (VMIs). MV-kV and kV-kV VMIs were compared with single-energy images. Results: The 80 kV-140 kV pair typically yielded the best SNRs, but for bone thicknesses >8 cm, the detunedMV-80 kV pair surpassed it. Peak MV-kV SNR was achieved with ∼90% dose allocated to the MV spectrum. In CT simulations of the pelvis with a steel implant, MV-kV VMIs yielded a higher contrast-to-noise ratio (CNR) than single-energy CT and kV-kV DE-CT. Without steel, the MV-kV VMIs produced higher contrast but lower CNR than single-energy CT. Conclusions: This work analyzes MV-kV DE-CT imaging and assesses its potential advantages. The technique may be used for metal artifact correction and generation of VMIs with higher native contrast than single-energy CT. Improved denoising is generally necessary for greater CNR without metal.

Emphysema Quantifications With CT Scan: Assessing the Effects of Acquisition Protocols and Imaging Parameters Using Virtual Imaging Trials.

BACKGROUND: CT scan has notable potential to quantify the severity and progression of emphysema in patients. Such quantification should ideally reflect the true attributes and pathologic conditions of subjects, not scanner parameters. To achieve such an objective, the effects of the scanner conditions need to be understood so the influence can be mitigated. RESEARCH QUESTION: How do CT scan imaging parameters affect the accuracy of emphysema-based quantifications and biomarkers? STUDY DESIGN AND METHODS: Twenty anthropomorphic digital phantoms were developed with diverse anatomic attributes and emphysema abnormalities informed by a real COPD cohort. The phantoms were input to a validated CT scan simulator (DukeSim), modeling a commercial scanner (Siemens Flash). Virtual images were acquired under various clinical conditions of dose levels, tube current modulations (TCM), and reconstruction techniques and kernels. The images were analyzed to evaluate the effects of imaging parameters on the accuracy of density-based quantifications (percent of lung voxels with HU < -950 [LAA-950] and 15th percentile of lung histogram HU [Perc15]) across varied subjects. Paired t tests were performed to explore statistical differences between any two imaging conditions. RESULTS: The most accurate imaging condition corresponded to the highest acquired dose (100 mAs) and iterative reconstruction (SAFIRE) with the smooth kernel of I31, where the measurement errors (difference between measurement and ground truth) were 35 ± 3 Hounsfield Units (HU), -4% ± 5%, and 26 ± 10 HU (average ± SD), for the mean lung HU, LAA-950, and Perc15, respectively. Without TCM and at the I31 kernel, increase of dose (20 to 100 mAs) improved the lung mean absolute error (MAE) by 4.2 ± 2.3 HU (average ± SD). TCM did not contribute to a systematic improvement of lung MAE. INTERPRETATION: The results highlight that although CT scan quantification is possible, its reliability is impacted by the choice of imaging parameters. The developed virtual imaging trial platform in this study enables comprehensive evaluation of CT scan methods in reliable quantifications, an effort that cannot be readily made with patient images or simplistic physical phantoms.

Scanner-specific validation of a CT simulator using a COPD-emulated anthropomorphic phantom.

Traditional methods of quantitative analysis of CT images typically involve working with patient data, which is often expensive and limited in terms of ground truth. To counter these restrictions, quantitative assessments can instead be made through Virtual Imaging Trials (VITs) which simulate the CT imaging process. This study sought to validate DukeSim (a scanner-specific CT simulator) utilizing clinically relevant biomarkers for a customized anthropomorphic chest phantom. The physical phantom was imaged utilizing two commercial CT scanners (Siemens Somatom Force and Definition Flash) with varying imaging parameters. A computational version of the phantom was simulated utilizing DukeSim for each corresponding real acquisition. Biomarkers were computed and compared between the real and virtually acquired CT images to assess the validity of DukeSim. The simulated images closely matched the real images both qualitatively and quantitatively, with the average biomarker percent difference of 3.84% (range 0.19% to 18.27%). Results showed that DukeSim is reasonably well validated across various patient imaging conditions and scanners, which indicates the utility of DukeSim for further VIT studies where real patient data may not be feasible.

A scanner-specific framework for simulating CT images with tube current modulation.

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 33.0 BMI phantom. This illustrates the utility of the developed framework for future optimization studies of TCM parameters and, more broadly, large-scale VITs with scanner-specific TCM.

Dissatisfaction after laparoscopic Heller myotomy: The truth is easy to swallow.

BACKGROUND: Although laparoscopic Heller myotomy has been shown to well palliate symptoms of achalasia, we have observed a small subset of patients who are "Dissatisfied". This study was undertaken to identify the causes of their dissatisfaction. STUDY DESIGN: Patients undergoing laparoscopic Heller myotomy from 1992 to 2015 were prospectively followed. Using a Likert scale, patients rated their symptom frequency/severity before and after the procedure. Patients graded their experience from "Very Satisfying" to "Very Unsatisfying." RESULTS: 647 patients underwent laparoscopic Heller myotomy. Fifty (8%) patients, median age 57 years and BMI 24 kg/m2 reported dissatisfaction at follow-up subsequent to myotomy. "Dissatisfied" patients were more likely to have undergone prior abdominal operations (p = 0.01) or previous myotomies (p = 0.02). "Dissatisfied" patients had a greater incidence of diverticulectomy (p = 0.03) and had longer postoperative LOS (p = 0.01). Symptom frequency/severity persisted after myotomy for dissatisfied patients (p > 0.05). CONCLUSION: Dissatisfaction after laparoscopic Heller myotomy is directly related to persistent/recurrent symptoms. Previous abdominal operations/myotomies, diverticulectomies, and longer LOS are predictors of dissatisfaction. With this understanding, we can identify patients who might be more prone to dissatisfaction.

Age and Achalasia: How Does Age Affect Patient Presentation, Hospital Course, and Surgical Outcomes?

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.