Non-invasive assessment of skeletal kinetics using fluorine-18 fluoride positron emission tomography: evaluation of image and population-derived arterial input functions.

To measure regional skeletal kinetics using fluorine-18 fluoride positron emission tomography (PET) it is necessary to know the concentration of radioactive tracer being delivered to bone by arterial plasma with relation to time, the arterial input function (IFa). Methods by which IFa can be derived without arterial sampling are attractive because of their relative technical simplicity and the reduction in possible morbidity to the subject. We have compared the use of a scaled population input function (IFp) and a corrected image-derived input function from the aorta (IFi) with an IFa directly measured from a radial artery line in ten normal postmenopausal women. Both of the aforementioned methods rely only on a small number of discrete venous samples. Each subject had a dynamic PET acquisition of the lumbar spine performed after the intravenous injection of 180 MBq (18)F-fluoride. Both the IFp and the IFi were compared with the IFa in terms of the accuracy of determination of six parameters. These were: plasma clearance of fluoride to bone mineral (K(i)), unidirectional plasma clearance to total bone tissue (K(1)) and individual rate constants k(2), k(3) and k(4), calculated using non-linear regression with a three-compartment model, and the plasma clearance to bone mineral calculated using the Patlak method (K(pat)). For both the IFp and the IFi method the root mean square errors for K(pat) and K(i) were similar and small (<8.2%). The errors in determining K(1) and the rate constants k(2) to k(4) are larger by either method, but with a small advantage using the IFp method. It is concluded that the use of either non-invasive method for determining the arterial plasma input function is suitable for the measurement of the most important parameters, K(i) and K(pat), in these subjects.

Speech-related visualization of laryngeal muscles with fluorine-18-FDG.

UNLABELLED: This study describes the physiological uptake of 18F-fluoro-2-deoxyglucose (FDG) by the laryngeal muscles secondary to activation of the patient's vocal folds and related laryngeal muscles during speech. METHODS: Twenty-four patients undergoing routine PET scans were randomized into two groups to ascertain the relationship between FDG uptake in the laryngeal region and speech. One group was assigned to talk and the other group remained silent during the injection and uptake period of FDG. RESULTS: FDG uptake in the laryngeal muscles in the scans was correlated with speech. Patients who spoke continually during the uptake period had high-grade FDG uptake, those who spoke intermittently had low-grade uptake and those who remained silent had no detectable increase in FDG uptake in the region of the larynx. CONCLUSION: The relationship between the degree of laryngeal muscle uptake and speech provides useful information to allow differentiation of physiological from pathological uptake in the neck.

The use of low-dose intravenous insulin in clinical myocardial F-18 FDG PET scanning.

The effectiveness of low-dose intravenous insulin boluses to improve study quality in F-18 FDG myocardial scans is investigated. Seventeen patients were imaged using a protocol in which only diabetic patients with fasting blood glucose levels > 8 mmol/l were given insulin. Fifty-three patients were imaged using a protocol in which all patients were given 1-3 IU intravenously of insulin immediately before F-18 FDG injection, based on fasting blood glucose levels. Scan quality was rated as poor, good, or excellent. Using the conventional protocol, 29% of the scans were poor quality (uniterpretable), 47% were good, and 23% were excellent. Using the low-dose intravenous insulin boluses protocol; 2% were poor, 53% were good, and 45% were excellent (P = 0.01). There were no significant differences in the proportion of diabetic patients, age, or fasting blood glucose levels. Low-dose intravenous insulin bolus is an easy and safe method of improving myocardial F-18 FDG scan quality in nondiabetic and diabetic patients.

Salivary gland scintigraphy--a suitable substitute for sialography?

By comparing 27 patients who had both scintigraphy and sialography in the assessment of salivary gland disease, scintigraphy has been shown to correlate well with abnormal sialograms. It is suggested that scintigraphy could become the initial screening procedure in the assessment of salivary gland disease. A normal scintiscan is unlikely to miss significant pathology (as demonstrated by sialography), but sialography must always be performed if there is a suspicion of duct obstruction on scintigraphy. Patients suspected of focal salivary gland pathology such as tumour have not been investigated. The series documents the findings in patients who presented with facial pain, swelling or xerostomia suggesting sialadenitis, duct occlusion or Sjögren's syndrome.