A new method for determining the glomerular filtration rate was analysed prospectively. The method uses an x ray fluorescence technique to measure disappearance from the plasma of injected non-ionic iodinated contrast media. Eighty seven patients were studied. Fifty four had an intravenous dose of 100 ml iohexol (Omnipaque) and 33 had 50 ml iohexol. Clearances of chromium-51 labelled edetic acid (51Cr-EDTA) were measured simultaneously. In the patients given 100 ml iohexol there was excellent correlation with 51Cr-EDTA clearance (r = 0.90). The correlation using 50 ml iohexol was also good (r = 0.85). Correlation between creatinine clearance and clearance of 51Cr-EDTA in 33 patients was less satisfactory (r = 0.69). There were no adverse reactions to the contrast media. The equipment used for measuring contrast clearance was robust and simple to operate. Freezing plasma samples in 10 studies and re-examining them weekly for six weeks showed no significant variation in results; hence reproducibility was good. This new and accurate method for determining the glomerular filtration rate merits further study and might find a useful place in routine clinical practice.

https://www.bmj.com/content/bmj/293/6541/234.full.pdf

Accuracy and reproducibility of a new contrast clearance method for the determination of glomerular filtration rate.

Measurement of the plasma clearance of urographic contrast media for the determination of glomerular filtration rate

We have been developing an X-ray fluorescence system designed to determine iodine distribution and content in the thyroid. The X-ray fluorescence unit is composed of a 80 kV X-ray excitation beam and a Si(Li) semi-conductor detector. The angle between the X-ray beam and the axis of the detector is 24°. Two single channel analyzers (SCA) are used, the first one corresponding to the Kα peak and the other to the background. The SCA signals are digitised so that the two corresponding images may be processed using a computer.

Application of x-ray fluorescence to the study of iodine distribution and content in the thyroid.

The relationship between thyroid iodine content (TIC) measured by x-ray fluorescence and serum TSH, T4, and T3 levels was investigated under iodide supplementation (0.5 mg/day for 1 to 9 mo). In five euthyroid control patients, whose TIC ranged from 2.5 to 14 mg, the TIC increased from 1.5 to 4 mg after 4 wk of treatment and had a tendency to plateau when the treatment was pursued. No significant changes in serum T4, T3, and TSH levels have been observed in these control subjects. Fourteen patients with autoimmune thyroiditis with low TIC (0-5 mg) were also studied. In six patients, the TIC increased significantly (3-10 mg over initial value after 3-7 mo of treatment). In parallel, there was a significant increase in serum T4 levels (35-150% over initial value) while T3 levels were modified in only two patients. In five patients serum TSH level decreased and was two- to seven-fold lower than before treatment whatever was its initial value; however, the spectrum of changes varied among patients from slight increase to a complete normalization of hormonosynthesis. In the eight other patients, iodide supplementation aggravated the thyroid disorders during the first months of treatment. The thyroid hormone blood levels dropped significantly in six patients (percent decrease below initial value: 20-100%) and was unchanged in the two others. An increase in the TSH blood level (X2-6) was observed in all patients except one. Concomitantly, the iodine stores were progressively depleted in three patients, unchanged in three and increased in two. When iodide treatment was pursued, an escape from this organification block was observed in two patients.

https://jnm.snmjournals.org/content/26/2/133.full.pdf

Thyroid iodine content and serum thyroid hormone levels in autoimmune thyroiditis: effect of iodide supplementation.

X-ray fluorescence analysis (XRF) is a non-invasive method that can be used for in vivo determination of thyroid iodine content. System calibrations with phantoms resembling the neck may give misleading results in the cases when the measurement situation largely differs from the calibration situation. In such cases, Monte Carlo (MC) simulations offer a possibility of improving the calibration by better accounting for individual features of the measured subjects. This study investigates the prospects of implementing MC simulations in a calibration procedure applicable to in vivo XRF measurements. Simulations were performed with Penelope 2005 to examine a procedure where a parameter, independent of the iodine concentration, was used to get an estimate of the expected detector signal if the thyroid had been measured outside the neck. An attempt to increase the simulation speed and reduce the variance by exclusion of electrons and by implementation of interaction forcing was conducted. Special attention was given to the geometry features: analysed volume, source-sample-detector distances, thyroid lobe size and position in the neck. Implementation of interaction forcing and exclusion of electrons had no obvious adverse effect on the quotients while the simulation time involved in an individual calibration was low enough to be clinically feasible.

https://iopscience.iop.org/article/10.1088/0031-9155/52/7/015/pdf

A Monte Carlo (MC) based individual calibration method for in vivo x-ray fluorescence analysis (XRF).

A static x-ray fluorescent technique utilizing an 241Am source of low activity and a wide view diverging collimator which allows in vivo determination of the concentration and total content of iodine in the thyroid is described. Determinations of normal thyroidal iodine concentration and total iodine content were as follows: 0.40 mg/g and 10.6 mg for 16 men, and 0.67 mg/g and 17.6 mg for 14 women. This fluorescent system has been applied to 70 patients to date. Thyroidal iodine concentrations in patients with Graves' disease were approximately equal to those in healthy suspects, and little change was observed among the concentrations in patients before, during, or after treatment. In most of the patients with chronic or subacute thyroiditis, concentrations levels were lower.

N Sekita

Papers

Quantitative in vivo measurement of thyroidal iodine content by static x-ray fluorescent technique: some preliminary clinical observations.