Evaluation of Hot Nodules of Thyroid Gland Using Tc-99m Pertechnetate: a Novel Approach Using Quantitative Single-Photon Emission Computed Tomography/Computed Tomography

Artificial intelligence-based CT-free quantitative thyroid SPECT for thyrotoxicosis: study protocol of a multicentre, prospective, non-inferiority study

INTRODUCTION

Technetium thyroid uptake (TcTU) measured by single-photon emission CT/CT (SPECT/CT) is an important diagnostic tool for the differential diagnosis of Graves' disease and destructive thyroiditis. Artificial intelligence (AI) may reduce CT-induced radiation exposure by substituting the role of CT in attenuation correction (AC) and thyroid segmentation, thus realising CT-free SPECT. This study aims to compare the diagnostic accuracy for the differential diagnosis of thyrotoxicosis between CT-free SPECT and SPECT/CT.

METHODS AND ANALYSIS

The AI-based CT-free SPECT is a single-blind, multicentre, prospective, non-inferiority, clinical trial with a paired design conducted in the Republic of Korea. Eligible participants are adult (≥19 years old) thyrotoxicosis patients without a previous history of hyperthyroidism or hypothyroidism. Approximately 160 subjects will be screened for quantitative thyroid SPECT/CT using Tc-99m pertechnetate. CT-free thyroid SPECT will be realised using only SPECT data by the trained convolutional neural networks. TcTU will be calculated by SPECT/CT and CT-free SPECT in each subject. The primary endpoint is the accuracy of diagnosing Graves' disease using TcTU. The trial will continue until 152 completed datasets have been enrolled to assess whether the 95% (two-sided) lower confidence limit of the accuracy difference (CT-free SPECT accuracy-SPECT/CT accuracy) for Graves' disease is greater than -0.1. The secondary endpoints include the accuracy of diagnosing destructive thyroiditis and predicting the need for antithyroid drug prescription within 1 month of the SPECT/CT.

ETHICS AND DISSEMINATION

The study protocol has been approved by the institutional review board of Seoul National University Bundang Hospital (IRB No. B-2304-824-301), Konkuk University Medical Center (IRB No. 2023-05-022-006) and Chonnam National University Hospital (IRB No. CNUH-2023-108). Findings will be disseminated as reports, presentations and peer-reviewed journal articles.

TRIAL REGISTRATION NUMBER

KCT0008387, Clinical Research Information Service of the Republic of Korea (CRIS).

The determination of the optimal threshold on measurement of thyroid volume using quantitative SPECT/CT for Graves' hyperthyroidism

PURPOSE

To investigate the optimal threshold for measuring thyroid volume in patients with Grave's hyperthyroidism (GH) by SPECT/CT.

MATERIALS AND METHODS

A 53 mL butterfly-shaped hollow container made of two 45-degree transparent elbows was put into a NEMA IEC phantom tank. The butterfly-shaped container and the tank were then filled with Na99mTcO4 of different radioactive concentrations, respectively, which could simulate thyroid gland with GH by different target-to-background ratios (T/B) (200:1, 600:1, 1000:1). The different T/B of planar imaging and SPECT/CT were acquired by a Discovery NM/CT 670 Pro SPECT/CT. With Thyroid software (Version 4.0) of GE-Xeleris workstation, the region of the thyroid gland in planar imaging was delineated. The thyroid area and average long diameter of both lobes were substituted into the Allen formula to calculate the thyroid volume. The calculation error was compared with the actual volume. Q-Metrix software was used to perform CT-based attenuation correction, scatter correction, resolution recovery. Ordered-subsets expectation maximization was used to reconstruct SPECT data. 20%, 25%, 30%, 40%, 50%, 60% thresholds were selected to automatically delineate the volume of interest and compared with the real volume, which determinated the optimal threshold. We measured the thyroid volume of 40 GH patients using the threshold and compared the volumes obtained by planar imaging and ultrasound three-dimensional. The differences of the volumes with different T/B and thresholds were compared by the ANOVA and least significant difference t test. The volumes delineated by SPECT/CT were evaluated using ANOVA, least significant difference t test, correlation analysis and, linear regression and Bland-Altman concordance test plot. The differences and consistency of thyroid volume were compared among the above three methods.

RESULTS

There was no significant difference in the results between different T/B models (P > 0.05). The thyroid volume calculated by the planar imaging formula method was higher than the real volume, with an average overestimation of 22.81%. The volumes delineated by SPECT/CT threshold automatically decreased while the threshold increased. There were significant differences between groups with different thresholds (P < 0.001). With an average error of 3.73%, the thyroid volume analyzed by the threshold of 25% was close to the results of ultrasound measurement (P > 0.05). Thyroid volume measured by planar imaging method was significantly higher than ultrasound and SPECT/CT threshold automatic delineation method (P < 0.05). The agreement between the SPECT/CT 25% threshold and ultrasound (r = 0.956, b = 0.961) was better than that between the planar imaging and ultrasound (r = 0.590, b = 0.574). The Bland-Altman plot also showed that the thyroid volume measured by the 25% threshold automatic delineation method was in good agreement with the ultrasound measurement.

CONCLUSIONS

The T/B has no effect on the measurement of thyroid volume in GH patients; planar imaging method can significantly overestimate thyroid volume in GH patients, and 25% threshold automatic delineation method can obtain more accurate thyroid volume in GH patients.

CT-free quantitative SPECT for automatic evaluation of %thyroid uptake based on deep-learning

PURPOSE

Quantitative thyroid single-photon emission computed tomography/computed tomography (SPECT/CT) requires computed tomography (CT)-based attenuation correction and manual thyroid segmentation on CT for %thyroid uptake measurements. Here, we aimed to develop a deep-learning-based CT-free quantitative thyroid SPECT that can generate an attenuation map (μ-map) and automatically segment the thyroid.

METHODS

Quantitative thyroid SPECT/CT data (n = 650) were retrospectively analyzed. Typical 3D U-Nets were used for the μ-map generation and automatic thyroid segmentation. Primary emission and scattering SPECTs were inputted to generate a μ-map, and the original μ-map from CT was labeled (268 and 30 for training and validation, respectively). The generated μ-map and primary emission SPECT were inputted for the automatic thyroid segmentation, and the manual thyroid segmentation was labeled (280 and 36 for training and validation, respectively). Other thyroid SPECT/CT (n = 36) and salivary SPECT/CT (n = 29) were employed for verification.

RESULTS

The synthetic μ-map demonstrated a strong correlation (R² = 0.972) and minimum error (mean square error = 0.936 × 10^-4, %normalized mean absolute error = 0.999%) of attenuation coefficients when compared to the ground truth (n = 30). Compared to manual segmentation, the automatic thyroid segmentation was excellent with a Dice similarity coefficient of 0.767, minimal thyroid volume difference of - 0.72 mL, and a short 95% Hausdorff distance of 9.416 mm (n = 36). Additionally, %thyroid uptake by synthetic μ-map and automatic thyroid segmentation (CT-free SPECT) was similar to that by the original μ-map and manual thyroid segmentation (SPECT/CT) (3.772 ± 5.735% vs. 3.682 ± 5.516%, p = 0.1090) (n = 36). Furthermore, the synthetic μ-map generation and automatic thyroid segmentation were successfully performed in the salivary SPECT/CT using the deep-learning algorithms trained by thyroid SPECT/CT (n = 29).

CONCLUSION

CT-free quantitative SPECT for automatic evaluation of %thyroid uptake can be realized by deep-learning.

Subclinical hyperthyroidism in children

Subclinical hyperthyroidism (SH) is defined as serum thyroid-stimulating hormone (TSH) below the lower limit of the reference range in the presence of normal free T4 and free T3 levels. Depending on the degree of TSH suppression, SH could be defined as mild (TSH, 0.1-0.45 mU/L) or severe (TSH<0.1 mU/L). Patients with SH are often asymptomatic when symptoms are present, they are similar to the symptoms in patients with overt hyperthyroidism, although they are usually milder. The management of the SH is uncertain and should be individualized. We present this review after an extensive literature search and long-standing clinical experience. This review provides the prevalence, causes, clinical presentation, investigation, and therapeutic approach of SH in children.

KSNM 60 in General Nuclear Medicine: the Old Dream Comes True

Since the establishment of the Korean Society of Nuclear Medicine (KSNM) in 1961 by Professor Munho Lee, the KSNM has been progressing in various medical fields. Many papers have been published in the Korean Journal of Nuclear Medicine (KJNM), the official journal of KSNM, since 1967 and other domestic/international journals. Here, we tried to highlight the academic activities of KSNM members from the perspective of general nuclear medicine. After the introduction of the ⁹⁹Mo/^99mTc generator, general nuclear medicine has widened the field of clinical application with the advancement of imaging technology and emerging new radiopharmaceuticals; however, there have been many ups and downs. Treatment, as well as diagnosis, was a major concern in Korean nuclear medicine. With the recent advent of single-photon emission computed tomography/computed tomography, we hope that our old dream (diagnosis and treatment under the same principle of nuclear medicine) comes true.

A retrospective multicenter study of quantitative bone SPECT/CT to predict the surgical removal of the accessory navicular bone

OBJECTIVE

The maximum standardized uptake value (SUVmax) in single-photon emission computed tomography/computed tomography (SPECT/CT) can help quantify disease activity of the accessory navicular bone (ANB). In this multicenter quantitative bone SPECT/CT study, we investigated whether SUVmax was correlated with ANB severity, thereby allowing prediction of surgical resection for ANB treatment.

METHODS

Two-hundred forty-six patients (men:women = 135:111, mean age = 39.3 years), who had undergone quantitative Tc-99m diphosphonate SPECT/CT of the feet, were recruited from four hospitals. SUVmax was measured using vendor-provided quantitation software. The SUVmax values were compared in relation to ANB type (type 1 = 62, type 2 = 136 and type 3 = 14), presence of pain and surgical treatment.

RESULTS

SUVmax (mean ± SD) was the highest in type 2 ANB (4.41 ± 5.2; P = 0.0101). The 17 resected ANBs showed greater SUVmax (8.27 ± 5.23; P < 0.0001) than the 141 asymptomatic ANBs (2.30 ± 1.68) or the 54 symptomatic ANBs without surgery (6.15 ± 4.40). Since surgery is exclusively indicated for ANB type 2, surgical resection was investigated only in these cases. In univariate analysis, young age and SUVmax were significantly associated with surgical treatment, but only SUVmax was a significant predictor of surgery in multivariate analysis (P < 0.0001). Type 2 ANBs were treated by surgery in 32.5% (13/40) of the cases when SUVmax was ≥5, and in only 1.35% (1/74) of the cases when SUVmax was <5 (P < 0.0001).

CONCLUSION

ANB disease activity and excision were strongly associated with the SUVmax derived from quantitative bone SPECT/CT. Our study suggests an absolute SUVmax cutoff for ultimate ANB surgical treatment, but additional prospective studies are required to validate this finding.

Thyroid hemiagenesis with a TI-RADS 2 nodule in the contralateral lobe

Background

Thyroid hemiagenesis is a rare congenital anomaly in which one lobe of the thyroid gland fails to develop. There is an increased incidence of associated thyroid disorders in patients with thyroid hemiagenesis.

Case presentation

A 32-year-old Ugandan woman presented with a complaint of painless neck swelling of 3-months duration. The swelling was associated with a globus sensation. There was no history of thyroid – related problems or treatment prior to this presentation. Physical examination demonstrated a mobile right thyroid swelling without an obvious nodular contour. Neck ultrasound showed an absent left lobe of thyroid gland, a right lobe with a solitary nodule scoring two points on the Thyroid Imaging, Reporting and Data System (TI-RADS) and an isthmus in situ. Extensive search for possible ectopic thyroid tissue was negative. She was biochemically euthyroid. The patient was counseled about thyroid hemiagenesis and was put on a regular follow up in the clinic for the TI-RADS 2 nodule.

Conclusion

Thyroid hemiagenesis is often associated with other thyroid disorders. Its diagnosis should prompt an active search for other associated morphological or functional thyroid abnormalities.

Quantitative salivary gland SPECT/CT using deep convolutional neural networks

Quantitative single-photon emission computed tomography/computed tomography (SPECT/CT) using Tc-99m pertechnetate aids in evaluating salivary gland function. However, gland segmentation and quantitation of gland uptake is challenging. We develop a salivary gland SPECT/CT with automated segmentation using a deep convolutional neural network (CNN). The protocol comprises SPECT/CT at 20 min, sialagogue stimulation, and SPECT at 40 min post-injection of Tc-99m pertechnetate (555 MBq). The 40-min SPECT was reconstructed using the 20-min CT after misregistration correction. Manual salivary gland segmentation for %injected dose (%ID) by human experts proved highly reproducible, but took 15 min per scan. An automatic salivary segmentation method was developed using a modified 3D U-Net for end-to-end learning from the human experts (n = 333). The automatic segmentation performed comparably with human experts in voxel-wise comparison (mean Dice similarity coefficient of 0.81 for parotid and 0.79 for submandibular, respectively) and gland %ID correlation (R2 = 0.93 parotid, R2 = 0.95 submandibular) with an operating time less than 1 min. The algorithm generated results that were comparable to the reference data. In conclusion, with the aid of a CNN, we developed a quantitative salivary gland SPECT/CT protocol feasible for clinical applications. The method saves analysis time and manual effort while reducing patients' radiation exposure.

Can the function of the tubarial glands be evaluated using [99mTc]pertechnetate SPECT/CT, [18F]FDG PET/CT, and [11C]methionine PET/CT?

BACKGROUND

The tubarial glands (TGs) are recently reported as newly found salivary gland structures that can be organs at risk predominantly localized in the tori tubarius in the nasopharynx using prostate-specific membrane antigen positron emission tomography/computed tomography (PSMA PET/CT). The aims of this study were to analyze uptake in the TGs compared with that in the other salivary glands and palatine tonsils using [^99mTc]pertechnetate SPECT/CT, [¹⁸F]FDG PET/CT, and [¹¹C]methionine PET/CT and to confirm whether these three imaging modalities are useful in evaluating the physiological function of the TGs. Twelve and 130 patients, who underwent [^99mTc]pertechnetate SPECT/CT and [¹⁸F]FDG/[¹¹C]methionine PET/CT, respectively, were retrospectively included. [^99mTc]pertechnetate uptake in the tori tubarius was visually assessed and semiquantitatively compared with that in the background, parotid salivary glands (PSGs), submandibular salivary glands (SmSGs), and sublingual salivary glands (SlSGs). Correlations of [¹⁸F]FDG and [¹¹C]methionine uptakes in the tori tubarius with those in the other three salivary glands and palatine tonsils were analyzed.

RESULTS

[^99mTc]pertechnetate uptake in the tori tubarius was invisible and was not significantly higher than that in the background. Both [¹⁸F]FDG and [¹¹C]methionine uptakes in the tori tubarius were correlated with that in the palatine tonsils (r = 0.56, p < 0.0001; r = 0.48, p < 0.0001, respectively). [¹⁸F]FDG uptake in the tori tubarius was not positively correlated with that in the PSGs, SmSGs, and SlSGs (r = - 0.19, p = 0.03; r = - 0.02, p = 0.81; r = 0.12, p = 0.17, respectively). [¹¹C]methionine uptake in the tori tubarius was correlated with that in the SmSGs and SlSGs (r = 0.24, p = 0.01; r = 0.32, p < 0.01, respectively), but not with that in the PSGs (r = 0.16, p = 0.08).

CONCLUSIONS

The TGs were undetectable on [^99mTc]pertechnetate SPECT/CT. Both [¹⁸F]FDG and [¹¹C]methionine uptakes in the tori tubarius were clearly affected by that in the palatine tonsils and was little related to that in the other salivary glands. Therefore, it seems difficult to evaluate the physiological function of the TGs as salivary glands using [^99mTc]pertechnetate SPECT/CT, [¹⁸F]FDG PET/CT, and [¹¹C]methionine PET/CT imaging.

The Usefulness of Maximum Standardized Uptake Value at the Delayed Phase of Tc-99m sestamibi single-photon emission computed tomography/computed tomography for Identification of Parathyroid Adenoma and Hyperplasia

Tc-99m sestamibi single-photon emission computed tomography/computed tomography (SPECT/CT) has been used to help surgeons explore the location of parathyroid diseases, but quantitative parameters have not been systemically investigated for this purpose. We aimed to establish objective criteria for adenoma and hyperplasia using the standardized uptake value (SUV) in patients with hyperparathyroidism.Thirty-nine hyperparathyroid patients (male/female: 17/22, age: 58.33 ± 11.69 years) with at least 1 uptake-positive lesion of any degree by visual assessment in preoperative Tc-99m sestamibi quantitative SPECT/CT were included from Oct 2015 to Oct 2017. Pathologically, 44 lesions (32 adenomas and 12 hyperplasia) were identified. All patients experienced normalized levels of intact parathyroid hormone immediately after surgery. Quantitative SPECT/CT was performed at 10 minute and 2 hour post injection of Tc-99m sestabmibi (dose = 740 MBq), and maximum SUV (SUVmax) was measured for the parathyroid lesions. Experienced pathologists evaluated the percentage cellular proportions of chief cells, oxyphil cells, and clear cells.SUVmax (g/mL) of adenomas, hyperplasia, and reference thyroid tissue were 12.92 ± 6.68, 7.90 ± 5.49, and 7.01 ± 2.62 at 10min (early phase), decreasing to 7.46 ± 5.66, 4.65 ± 3.14, and 2.21 ± 1.07 at 2 hour (delayed phase), respectively. The adenomas showed significantly higher SUVmax than both the hyperplasia (P = .0131) and reference thyroid tissue (P < .0001) along the early and delayed phases, but the SUVmax of the hyperplasia did not differ from that of the reference thyroid tissue (P = .4196). The adenomas and hyperplasia were discriminated from the reference thyroid tissue using a cutoff SUVmax of 3.26 at the delayed phase. The adenomas had lower %proportions of oxyphil cells than the hyperplasia (P = .0054), but its SUVmax at the delayed phase was positively correlated with the %proportions of mitochondria-abundant oxyphil cells (rho = 0.418, P = .0173). The hyperplasia showed no correlation between SUVmax and cellular proportions.SUVmax at the delayed phase in the Tc-99m sestamibi quantitative SPECT/CT was useful for the identification and differentiation of parathyroid lesions causing hyperparathyroidism.

Minimum Standardized Uptake Value from Quantitative Bone Single-Photon Emission Computed Tomography/Computed Tomography for Evaluation of Femoral Head Viability in Patients with Femoral Neck Fracture

Purpose

Bone single-photon emission computed tomography/computed tomography (SPECT/CT) has been widely used for evaluation of femoral head viability in patients with femoral neck fracture. The current study aimed to investigate utility of standardized uptake value (SUV) from quantitative bone SPECT/CT for assessment of femoral head viability.

Methods

From March 2015 to November 2018, quantitative bone SPECT/CT was performed in 9 patients with non-viable femoral head post femoral neck fracture and in 31 controls. Maximum (SUVmax), mean (SUVmean), and minimum standardized uptake values (SUVmin) were measured over femoral head and neck. Mann-Whitney U test with Bonferroni correction was used to compare SUVs of ipsilateral and contralateral femurs from femoral neck fracture patients with those of control femurs.

Results

As for femoral head viability, SUVmax and SUVmean were not significantly decreased in non-viable femoral heads compared to those in controls. Only the SUVmin was significantly reduced in non-viable femoral heads (mean ± standard deviation, 0.57 ± 0.38) than in controls (0.95 ± 0.26, p = 0.006) and contralateral femoral heads (1.36 ± 0.59, p = 0.008). The cutoff SUVmin of 0.61 (g/mL) yielded a sensitivity of 77.8% and specificity of 87.1% for detection of non-viable femoral heads (p = 0.006). Contralateral femoral necks of the femoral neck fracture patients showed significantly higher SUVmean and SUVmin (3.17 ± 1.20 and 1.64 ± 0.63) than those of controls (2.32 ± 0.53 and 1.04 ± 0.27; p = 0.021 and p = 0.002, respectively), which seemed to reflect weight bearing effect or metabolic derangement.

Conclusions

The non-viable femoral heads from the femoral neck fracture showed significantly reduced SUVmin. Quantitative bone SPECT/CT holds promise for objective evaluation of femoral head viability.

Clinical Applications of Technetium-99m Quantitative Single-Photon Emission Computed Tomography/Computed Tomography

Single-photon emission computed tomography/computed tomography (SPECT/CT) is an already established nuclear imaging modality. Co-registration of functional information (SPECT) with anatomical images (CT) paved the way to the wider application of SPECT. Recent advancements in quantitative SPECT/CT have made it possible to incorporate quantitative parameters, such as standardized uptake value (SUV) or %injected dose (%ID), in gamma camera imaging. This is indeed a paradigm shift in gamma camera imaging from qualitative to quantitative evaluation. In fact, such quantitative approaches of nuclear imaging have only been accomplished for positron emission tomography (PET) technology. Attenuation correction, scatter correction, and resolution recovery are the three main features that enabled quantitative SPECT/CT. Further technical improvements are being achieved for partial-volume correction, motion correction, and dead-time correction. The reported clinical applications for quantitative SPECT/CT are mainly related to Tc-99m-labeled radiopharmaceuticals: Tc-99m diphosphonate for bone/joint diseases, Tc-99m pertechnetate for thyroid function, and Tc-99m diethylenetriaminepentaacetic acid for measurement of glomerular filtration rate. Dosimetry before trans-arterial radio-embolization is also a promising application for Tc-99m macro-aggregated albumin. In this review, clinical applications of Tc-99m quantitative SPECT/CT will be discussed.