A three-dimensional second-derivative surface-detection algorithm for volume determination on SPECT images.

Most existing techniques for determining volumes on single-photon-emission computed tomography (SPECT) data employ thresholding, two-dimensional edge detection, or manual delineation of edges. These methods, however, are limited in both accuracy and applicability. In seeking to overcome these limitations, a truly three-dimensional (3D) second-derivative-based algorithm which can be implemented with relative ease has been developed. The method incorporates 3D matrix operators; these are convoluted with the SPECT count data in order to produce a 3D voxel map whose data elements correspond to the second derivative of counts in the image. This map is then searched, a suitable derivative-based edge-defining criterion being applied to each voxel position, in order to locate the derivative surface boundary which defines the volume. Validation is obtained using phantom data from 99Tcm-filled bottles of volumes 200, 580 and 2500 cm3 placed within a body-sized tank containing background activities set to give a range of contrasts between 1.00 and 0.75 (i.e. background 0% to 25%). The performance of the algorithm is encouraging: the volumes of the two larger bottles are determined to within a 3% accuracy without the need for any prior calibration, and the results obtained over all bottle sizes are found to be contrast independent to within approximately 4%.

The effect of phantom wall thickness on volume determination in SPET.

Assessment, using phantoms, of a a three-dimensional, second-derivative, surface-detection algorithm for accurately determining the volumes of structures in single photon emission tomography (SPET) has shown the performance of the algorithm to be highly dependent on phantom wall thickness. With a 30% background activity level, the volume of a 600-cm3 cylinder with wall thickness approximately 0.4 mm was measured to an accuracy of approximately 1%, whereas for an almost identical cylinder with a wall thickness of approximately 3 mm the measured volume was underestimated by about 14%. To further investigate this 'wall-thickness' effect, theoretically generated SPET data have been produced, simulating a set of low-contrast cylindrical phantoms with identical internal dimensions and wall thicknesses ranging from 0 to 6 mm. These image data have demonstrated a 10% reduction in the calculated volume for wall thicknesses as thin as 1 mm. A less acute dependence is also demonstrated for a threshold-based quantitation algorithm, where a wall thickness of 4-5 mm is required to produce an effect of similar magnitude. The underlying cause behind this 'wall-thickness' effect is undoubtedly the perturbation in the count profile across the surface boundary, which results form the cold region of the phantom wall. Thus, phantom wall thickness will have an effect on the performance of most automated quantitation techniques, both two- and three-dimensional, since the majority must incorporate some form of analysis on this count profile.

An assessment of finger doses received by staff while preparing and injecting radiopharmaceuticals.

Good working practice and legal obligation impose a duty on nuclear medicine departments to check syringe activities before administration to a patient. If syringe guards are used to reduce staff exposure while drawing up injections, the guard has to be removed to measure the activity in a conventional reentrant ionization chamber type calibrator. Alternatively, the activity may be checked in a purpose-built syringe calibrator which allows the assay of the activity in the syringe without the need to remove the syringe guard. Finger doses received during the dose preparation and injection are a cause for concern. This study investigated the finger and whole-body doses received when using each of these calibrators, and compared the results with those obtained by an operator who did not measure the dose at all. The results demonstrated that although the finger doses are small, measurement of the syringe activities in a conventional ionization chamber increases the dose by a factor of 2 above that which would occur if no activity measurements were made, whereas the use of the specialized syringe calibrator gave finger doses only marginally above those obtained with no activity measurement.

The use of dual-isotope imaging to compare the gastrointestinal transit of food and pancreatic enzyme pellets in cystic fibrosis patients.

Cystic fibrosis patients require pancreatic enzyme supplements to aid food digestion. It is suspected that incorrect delivery of this enzyme may result in both significant malabsorption and the development of strictures in the proximal colon caused by the high-dose supplement reaching this region before the food. Investigations into the drug's delivery were performed using dual-isotope imaging; a method was developed to directly label the enteric-coated enzyme pellets with 111In, re-applying the enteric coating afterwards, and this was then ingested with a pancake meal labelled with 99Tcm-tin colloid. Consecutive image data, acquired over a period of > or = 4 h using a dual-headed gamma camera, were analysed to assess intestinal transit. In-vitro stability checks on these labelling techniques were encouraging, showing < 2% 99Tcm and < 7% 111In elution over 90 min in hydrochloric acid. In 5 of the 12 patients studied to date, the pellets were seen to pass through significantly faster than the food, with a mean difference in 50% gastric emptying time of greater than 93 min. The mean absolute difference in emptying time for all 12 patients was > 67 min. Thus, a technique has been developed to effectively radiolabel pancreatic enzyme pellets, and analysis of dual-isotope images using this preparation, together with radiolabelled solid food, has demonstrated significant differences in the transit of these two substances through the gastrointestinal tract of some cystic fibrosis patients.

The clinical impact of a combined gamma camera/CT imaging system on somatostatin receptor imaging of neuroendocrine tumours.

AIM: With a combined gamma camera/CT imaging system, CT images are obtained which are inherently registered to the emission images and can be used for the attenuation correction of SPECT and for mapping the functional information from these nuclear medicine tomograms onto anatomy. The aim of this study was to evaluate the clinical impact of SPECT/CT using such a system for somatostatin receptor imaging (SRI) of neuroendocrine tumours. MATERIALS AND METHODS: SPECT/CT imaging with (111)In-Pentetreotide was performed on 29 consecutive patients, the majority of whom had carcinoid disease. All SPECT images were first reported in isolation and then re-reported with the addition of the CT images for functional anatomical mapping (FAM). RESULTS: Fifteen of the 29 SPECT images were reported as abnormal, and in 11 of these abnormal images (73%) FAM was found to either establish a previously unknown location (7/11) or change the location (4/11) of at least one lesion. The revised location could be independently confirmed in 64% of these cases. Confirmation of location was not possible in the other patients due to either a lack of other relevant investigations, or the fact that lesions seen in the SPECT images were not apparent in the other investigations. FAM affected patient management in 64% of the cases where the additional anatomical information caused a change in the reported location of lesions. CONCLUSION: These results imply that FAM can improve the reporting accuracy for SPECT SRI with significant impact on patient management.

Gastric emptying and intestinal transit of pancreatic enzyme supplements in cystic fibrosis.

OBJECTIVE: To investigate gastric emptying and intestinal transit of pelleted pancreatin in relation to food boluses. METHODS: Dual isotope scintigraphy combined with breath hydrogen sampling was used to track the concurrent gastric emptying and intestinal transit of 111indium labelled microspheres and a 99mtechnetium labelled tin colloid test meal. Twelve pancreatic insufficient cystic fibrosis patients aged 5 to 38 years performed the study. RESULTS: 50% gastric emptying times showed patient to patient variation. The mean discrepancy in 50% gastric emptying times between the two labels was > 67 minutes. Mean small bowel transit time for the food bolus was prolonged at 3.6 minutes. A significant correlation was seen between weight standard deviation score and 50% emptying time for pancreatin (r = +0.73). CONCLUSION: Gastric mixing of food and pancreatin may be limited by rapid emptying of microspheres. Patients with high dosage requirements could benefit from changing the pattern of their pancreatin supplementation.

Does salivary gland scintigraphy predict response to pilocarpine in patients with post-radiotherapy xerostomia?

This study was undertaken to determine whether standard salivary gland scintigraphy may be used for the objective assessment of salivary gland sialogogues, in particular oral pilocarpine, in the treatment of post-radiotherapy xerostomia. Nine patients, with xerostomia following radiotherapy to the head and neck region underwent salivary gland scintigraphy with technetium-99m pertechnetate (40 MBq) both before and following 1 month of oral pilocarpine (5 mg tds). For each scan, the percentage uptake in the first 14 min, the peak uptake, time to peak uptake and the percentage of activity excreted following lemon juice stimulation were calculated. The results were correlated with the subjective response as assessed by questionnaire and visual analogue scale. We found no correlation between subjective response and any of the four scan parameters analysed. We could not identify any parameter that predicted those patients who would respond to pilocarpine. In addition, only one parameter, the percentage of activity excreted following stimulation, correlated with previous dose of radiotherapy to the gland. In conclusion, in this study salivary gland scintigraphy did not appear to correlate with or predict response to oral pilocarpine. However, future studies might consider performing salivary gland scintigraphy prior to radiotherapy as well as at differing time points following the commencement of pilocarpine.