Citations

Abstract Channelized Hotelling model observer (CHO) methods were developed to assess performance of an x-ray angiography system. The analytical methods included correction for known bias error due to finite sampling. Detectability indices ( d ′ ) corresponding to disk-shaped objects with diameters in the range 0.5–4 mm were calculated. Application of the CHO for variable detector target dose (DTD) in the range 6–240 nGy frame −1 resulted in d ′ estimates which were as much as 2.9× greater than expected of a quantum limited system. Over-estimation of d ′ < ∼ 3.0 was presumed to be a result of bias error due to temporally variable non-stationary noise. Statistical theory which allows for independent contributions of ‘signal’ from a test object (o) and temporally variable non-stationary noise (ns) was developed. The theory demonstrates that the biased d β ′ is the sum of the detectability indices associated with the test object ( d o ′ ) and non-stationary noise ( d ns ′ ). Given the nature of the imaging system and the experimental methods, d o ′ cannot be directly determined independent of d ns ′ . However, methods to estimate d ns ′ independent of d o ′ were developed. In accordance with the theory, d ns ′ was subtracted from experimental estimates of d β ′ , providing an unbiased estimate of d o ′ . Estimates of d o ′ exhibited trends consistent with expectations of an angiography system that is quantum limited for high DTD and compromised by detector electronic readout noise for low DTD conditions. Results suggest that these methods provide d o ′ estimates which are accurate and precise for d o ′ ⩾ ∼ 1.0 . Further, results demonstrated that the source of bias was detector electronic readout noise. In summary, this work presents theory and methods to test for the presence of bias in Hotelling model observers due to temporally variable non-stationary noise and correct this bias when the temporally variable non-stationary noise is independent and additive with respect to the test object signal.

AbstractBackgroundNausea and vomiting are classic symptoms of gastroparesis. It remains unclear if characteristics of nausea and vomiting are similar in different etiologies of gastroparesis. The aims of this article were as follows: to describe characteristics of nausea and vomiting in patients with gastroparesis and to determine if there are differences in nausea and vomiting in diabetic (DG) and idiopathic gastroparesis (IG).MethodsGastroparetic patients enrolling in the NIDDK Gastroparesis Registry underwent assessment with history and questionnaires assessing symptoms, quality of life, and a questionnaire characterizing nausea and vomiting.Key ResultsOf 159 gastroparesis patients (107 IG, 52 DG), 96% experienced nausea, whereas 65% experienced vomiting. Nausea was predominant symptom in 28% and vomiting was predominant in 4%. Nausea was severe or very severe in 41%. PAGI‐SYM nausea/vomiting subscore was greater with increased vomiting severity, but not nausea severity in DG than IG. Nausea was related to meals in 71%; lasting most of the day in 41%. Increasing nausea severity was related to decreased quality of life. Nausea often preceded vomiting in 82% of patients and vomiting often relieved nausea in 30%. Vomiting was more common in DG (81%) compared to IG (57%; p = 0.004). Diabetic patients more often had vomiting in the morning before eating, during the night, and when not eating.Conclusions & InferencesNausea is present in essentially all patients with gastroparesis irrespective of cause and associated with decreased quality of life. In contrast, vomiting was more prevalent, more severe, and occurred more often in DG than IG. Thus, characteristics of vomiting differ in IG vs DG.