Precise intraoperative location of gastrointestinal bleeding with a hand-held counter. Work in progress

AGA technical review on the evaluation and management of occult and obscure gastrointestinal bleeding

This literature review and the recommendations therein were prepared for the American Gastroenterological Association Clinical Practice and Practice Economics committee. The paper was approved by the committee on May 16, 1999, and by the AGA governing board on July 18, 1999.

Probability modelling of a surgical probe for tumour detection

Probability functions for the output counts from a radiation detector probe are needed to implement Bayesian detection strategies or to assess performance of the probe. This paper presents methods for simulating a surgical probe designed for tumour detection to obtain statistical information for modelling probability functions of output data. Statistical models of pharmaceutical uptake in normal organs and tumours were estimated from animal and human data, and these models were combined with a digitised human torso phantom to create a large set of simulated patients. With the simulated patients and with a spatial map of the probe response, computer simulations of intraoperative probe measurements provided a large set of simulated probe data. Probability models derived from these data using maximum-likelihood methods helped to formulate the detection strategy and to evaluate the performance of the surgical probe.

Comparison of in vivo scintillation probes and gamma cameras for detection of small, deep tumours

An in vivo probe was compared with a gamma camera for the task of detecting radiolabelled tumour models in a water phantom. The probe, which contained a 1 cm diameter NaI(T1) detector, was designed and used by us for surgical staging studies of gynaecological patients. Tumours were spherical sources of different sizes and activities per unit volume of cobalt-57. The phantom was a tank of water (451) containing dissolved radioactivity to simulate background activity. Detector-to-source separations and tank depths were also varied. Camera images of 10 min duration were compared with probe counts of 15 s. For each configuration a large number of source and background runs were analysed using an ideal-observer ROC technique. Area under the ROC curve was used as the figure of merit. Results show that for approximately uniform background the probe should perform substantially better than the gamma camera in detecting small, deep tumours provided that the probe can be manoeuvred to within a few centimetres of the tumour. Mathematical modelling of our results indicates that this conclusion is not dependent on radiopharmaceutical dose, tumour uptake or camera type.