Design of a generic method for single dual-tracer PET imaging acquisition in clinical routine

Using different tracers in PET imaging can bring complementary information on tumor heterogeneities. Ideally, PET images of different tracers should be acquired simultaneously to avoid the bias induced by movement and physiological changes between sequential acquisitions. Previous studies have demonstrated the feasibility of recovering separated PET signals or parameters of two or more tracers injected (quasi-)simultaneously in a single acquisition. In this study, a generic framework in the context of dual-tracer PET acquisition is proposed where no strong kinetic assumptions nor specific tuning of parameters are required. The performances of the framework were assessed through simulations involving the combination of [¹⁸F]FCH and [¹⁸F]FDG injections, two protocols (90 and 60-minute acquisition durations) and various activity ratios between the two injections. Preclinical experiments with the same radiotracers were also conducted. Results demonstrate the ability of the method both to extract separated arterial input functions (AIF) from noisy image-derived input function (IDIF) and to separate the dynamic signals and further estimate kinetic parameters.
The compromise between bias and variance associated with the estimation of net influx rateK_ishows that it is preferable to use the second injected radiotracer with twice the activity of the first for both 90-minute [¹⁸F]FCH+[¹⁸F]FDG and 60-minute [¹⁸F]FDG+[¹⁸F]FCH protocols. In these optimal settings, the weighted mean-squared-error of the estimated AIF was always less than 7%. TheK_ibias was similar to the one of single-tracer acquisitions; below 5%. Compared to single-tracer results, the variance ofK_iwas twice more for 90-minute dual-tracer scenario and four times more for the 60-minute scenario. The generic design of the method makes it easy to use for other pairs of radiotracers and even for more than two tracers. The absence of strong kinetic assumptions and tuning parameters makes it suitable for a possible use in clinical routine.

99mTcO4-/99mTc-MIBI dual-tracer scintigraphy for preoperative localization of parathyroid adenomas

Objective

To investigate the accuracy of dual-tracer scintigraphy for locating parathyroid adenomas in patients with primary hyperparathyroidism (PHPT).

Methods

We reviewed 268 patients with PHPT. All patients underwent technetium-99m pertechnetate (^99mTcO₄^-) scintigraphy and technetium-99m methoxyisobutylisonitrile (^99mTc-MIBI) dual-tracer scintigraphy of the thyroid and parathyroid glands, respectively. ^99mTcO₄^- planar scintigraphy was carried out initially followed by dual-phase ^99mTc-MIBI single-photon emission computed tomography (SPECT)/CT the next day. The findings were combined and interpreted. Individual ^99mTc-MIBI and dual-tracer scintigraphy were both analyzed. The sensitivity, specificity, and accuracy were determined in relation to surgical findings. The average interval between scan and surgery was 13 days.

Results

The positive and negative predictive values of ^99mTc-MIBI SPECT/CT were 92.0% and 71.3%, respectively, and the sensitivity, specificity, and accuracy were 88.3%, 79.2%, and 85.8%, respectively. The positive and negative predictive values of dual-tracer scintigraphy were 96.3% and 82.3%, respectively, and the sensitivity, specificity, and accuracy were 92.9%, 90.3%, and 92.2%, respectively. Youden’s index for dual-tracer scintigraphy and ^99mTc-MIBI SPECT/CT were 0.83 and 0.63, respectively.

Conclusions

These finding suggest that ^99mTcO₄^- and ^99mTc-MIBI dual-tracer scintigraphy is more accurate than other scintigraphy methods for detecting parathyroid adenoma, and may thus be the most suitable imaging technique in patients with PHPT.

Clinical use of an opto-nuclear probe for hybrid sentinel node biopsy guidance: first results

INTRODUCTION

Guidelines advocate the use of combined detection techniques to achieve optimal results for sentinel node (SN) biopsy. The fluorescent and radioactive (dual-) tracer ICG-^99mTc-nanocolloid has been shown to facilitate SN biopsy in several indications. It was reported that an opto-nuclear probe permitted the detection of near-infrared fluorescence and gamma-rays. The aim of the current study was to evaluate this device in a large patient group and to test it in both open and laparoscopic surgery implications.

METHODS

Thirty-three patients scheduled for SN biopsy with the dual-tracer were retrospectively analyzed. Pre-operative lymphoscintigraphy was performed in all patients; in 18 patients (55%), a SPECT/CT scan was also performed. Radioactive and fluorescent signatures in the SNs were assessed in vivo and ex vivo using the opto-nuclear probe.

RESULTS

One or more SNs were identified in all patients (identification rate 100%). Planar lymphoscintigraphic images revealed 95 hot spots that were considered as SNs. This number increased to 103 SNs when SPECT/CT was used. During surgery, 106 SNs were excised. In vivo, the fluorescence mode of the opto-nuclear probe was able to locate 79 SNs (74.5%). When the gamma-ray detection option of the same probe was used, this number increased to 99 SNs (93.3%). Ex vivo analysis revealed fluorescence in 93.3% of the excised nodes and radioactivity in 95.2%.

CONCLUSIONS

This study underlines the feasibility of using the dual-tracer/opto-nuclear probe combination for SN resections. The use of the opto-nuclear technology has been extended to laparoscopic surgery. This study also underlines the fluorescence tracing can complement traditional radio-tracing approaches.