Diagnostic accuracy of SPECT/CT in parathyroid adenoma detection: impact of radiopharmaceutical choice and quality control practices

Abstract

Purpose

To evaluate the diagnostic accuracy of SPECT/CT for localizing parathyroid adenomas and to determine how radiopharmaceutical choice (MIBI vs. Myoview) and quality control (QC) practices affect detection performance and administered dose consistency in clinical practice.

Methods

This retrospective study included 136 patients who underwent dual-phase parathyroid scintigraphy with SPECT/CT at Al-Hada Armed Forces Hospital. Patients were classified into four groups according to radiopharmaceutical (MIBI or Myoview) and QC status (Regular or Irregular QC). Administered activity, detection accuracy, lesion localization, and concordance with surgical findings were assessed. Diagnostic performance was compared between SPECT/CT and planar imaging. Statistical analyses included ANOVA, χ² tests, and correlation analysis.

Results

SPECT/CT demonstrated significantly higher diagnostic accuracy than planar imaging across all groups. Regular QC conditions produced the most consistent administered activities and the highest detection rate (97.1%), whereas Irregular QC significantly reduced accuracy to 72.1%. MIBI showed superior performance under QC variability, maintaining higher sensitivity and more consistent lesion localization than Myoview. SPECT/CT also improved detection of ectopic and multi-gland disease compared with planar imaging.

Conclusion

SPECT/CT provides high diagnostic accuracy for parathyroid adenoma detection, but performance is strongly influenced by QC practices and, to a lesser extent, by radiopharmaceutical choice. Regular QC ensures optimal dose consistency and diagnostic reliability, while MIBI offers greater robustness under variable QC conditions. These findings support QC standardization and radiopharmaceutical selection as key determinants of improved clinical outcomes.

Introduction

In nuclear medicine, ensuring both diagnostic accuracy and patient safety requires not only optimal imaging technology but also strict adherence to quality control (QC) procedures (Morris et al. 2022). Single-photon emission computed tomography combined with computed tomography (SPECT/CT) has become the preferred modality for parathyroid adenoma localization, offering enhanced lesion detectability and precise anatomical correlation. However, diagnostic performance and radiation dose consistency in SPECT/CT are influenced by multiple operational variables—chief among them being the choice of radiopharmaceutical and the rigor of QC implementation (Spanu et al. 2014, Ovčariček et al. 2021).

Two radiotracers are commonly used in parathyroid scintigraphy: technetium-99 m (Tc-99 m) sestamibi (MIBI) and technetium-99 m tetrofosmin (Myoview). While both agents are lipophilic cationic compounds capable of localizing in hyperfunctioning parathyroid tissue, they exhibit different pharmacokinetics. MIBI has slower washout and higher mitochondrial retention, generally supporting more stable uptake in dual-phase imaging. Myoview, on the other hand, has faster clearance, potentially reducing imaging time but increasing susceptibility to timing errors and washout-related false negatives (Giordano et al. 2003). Despite these differences, tracer-specific effects on administered dose consistency and image quality under varying QC conditions remain underexplored in large clinical cohorts.

Routine QC—such as daily gamma camera uniformity testing, dose calibrator verification, and adherence to standardized injection protocols—is essential to maintain consistent administered activity and image quality. Irregular QC practices can lead to variability in administered dose, image degradation, and diagnostic uncertainty (Ovčariček et al. 2021). These effects are especially critical in the context of dose optimization and the establishment of Diagnostic Reference Levels (DRLs), which require accurate and reproducible activity measurements across patients and institutions (Dennis et al. 2018).

Recent evidence supports the growing role of advanced PET/CT imaging, particularly fluorine-18-fluorocholine (FCH) PET/CT, for the localization of parathyroid adenomas when conventional imaging modalities are inconclusive or negative. Studies have demonstrated that FCH PET/CT can significantly improve lesion localization compared with traditional techniques, especially in patients with ectopic or multiglandular disease, and may serve as a valuable second-line or even first-line modality in centers with availability and expertise. However, widespread use of PET/CT is currently limited by cost, access, and availability, which keeps SPECT/CT as the most accessible and practical option for routine preoperative parathyroid imaging (Chiu et al. 2025, Garnier et al. 2025, Ovčariček et al. 2025).

This study investigates how radiopharmaceutical selection and QC adherence influence administered dose consistency in parathyroid SPECT/CT. Using a dataset of 136 patients imaged under four defined conditions (MIBI/Myoview × Regular/Irregular QC), the analysis quantifies variability in technetium-99 m activity, stratified by sex, age, and imaging protocol. In parallel, detection and localization outcomes are compared to assess whether dose variation correlates with diagnostic accuracy. The findings aim to support protocol standardization, inform local DRL development, and reinforce the critical role of routine QC in nuclear medicine imaging.

Methods

This retrospective observational study analyzed the administered radiopharmaceutical activity and diagnostic performance of parathyroid SPECT/CT imaging in a cohort of 136 adult patients. All patients were referred for evaluation of suspected primary hyperparathyroidism and underwent dual-phase parathyroid imaging at Al-Hada Armed Forces Hospital (Taif, Saudi Arabia). The institutional review board approved the study protocol, and surgical findings served as the diagnostic reference standard for all imaging outcomes.

Patients were equally divided into four imaging groups (n = 34 per group), based on radiopharmaceutical type and adherence to quality control (QC) practices:

• Group 1 (G1): Technetium-99 m sestamibi (MIBI) with Regular QC.

• Group 2 (G2): Technetium-99 m tetrofosmin (Myoview) with Regular QC.

• Group 3 (G3): MIBI with Irregular QC.

• Group 4 (G4): Myoview with Irregular QC.

Radiopharmaceutical activities were prepared and administered according to institutional protocols. QC classification was based on the documented frequency and consistency of phantom testing, dose calibrator verification, and protocol adherence. “Regular QC” required daily phantom uniformity checks, calibrated injections, and compliance with standardized acquisition settings. “Irregular QC” involved inconsistent or missing documentation of these procedures.

Each patient underwent dual-phase imaging: early planar acquisition (15–30 min post-injection), delayed planar acquisition (90–150 min), and hybrid SPECT/CT performed on a dual-head gamma camera with low-dose non-contrast CT for attenuation correction and anatomical correlation. Hybrid SPECT/CT acquisition was performed after delayed planar imaging, approximately 90–150 min post-injection. Hybrid SPECT/CT acquisition was performed after delayed planar imaging, approximately 90–150 min post-injection.The injected activities were recorded in megabecquerels (MBq), and SPECT/CT outcomes were validated against surgical exploration and histopathology reports. Ectopic parathyroid adenomas were defined as glands located outside the typical posterior thyroid region, including mediastinal, retroesophageal, intrathymic, or carotid sheath locations. All included patients had surgically confirmed ectopic parathyroid adenomas. Cases with adenomas in typical posterior thyroid locations were excluded from the analysis. Therefore, all detection and localization outcomes in this study refer to ectopic lesions.

Primary quantitative outcomes included:

• Mean administered dose (MBq) by group.

• Dose consistency stratified by gender and age (< 55 vs. ≥ 55 years).

Secondary outcomes included:

• Detection rate (presence of adenoma confirmed by surgery).

• Localization accuracy (correct anatomical mapping by imaging).

Statistical analysis was conducted using SPSS version 26. Categorical variables were analyzed using Pearson’s χ² test or Fisher’s exact test where appropriate. Continuous variables such as MBq activity were compared using independent-samples t-tests or ANOVA. Statistical significance was defined as p < 0.05.

Results

Administered dose consistency across groups

The mean administered activity of technetium-99 m varied across the four imaging groups. Group 1 (MIBI with Regular QC) recorded the highest mean dose at 748.06 MBq. Group 3 (MIBI with Irregular QC) followed with 712.62 MBq. Group 2 (Myoview with Regular QC) showed a mean of 709.85 MBq, while Group 4 (Myoview with Irregular QC) had the lowest at 692.65 MBq. Regular QC produced lower variability for Myoview (SD = 9.49 MBq vs. 13.20 MBq), whereas for MIBI the standard deviation under Regular QC (SD = 13.60 MBq) was slightly higher than under Irregular QC (SD = 11.07 MBq)Variability in administered activity was lower in Regular QC groups, with standard deviations of 13.6 MBq for MIBI and 9.5 MBq for Myoview, compared with higher variability in Irregular QC groups (11.1 MBq for MIBI and 13.2 MBq for Myoview), as shown in Table 1.

Table 1.

Mean and standard deviation of administered technetium-99 m activity for each imaging group, stratified by tracer and quality control (QC) type. Regular QC groups demonstrated lower standard deviation, indicating tighter dose consistency

Group	Radiopharmaceutical	QC Type	Mean Dose (MBq)	Standard Deviation (MBq)
G1	MIBI	Regular	748.06	13.60
G2	Myoview	Regular	709.85	9.49
G3	MIBI	Irregular	712.62	11.07
G4	Myoview	Irregular	692.65	13.20

The slightly higher SD observed for MIBI under Regular QC likely reflects broader clinical dosing ranges for sestamibi; however, when both tracers are considered, Regular QC still demonstrates overall tighter dose control than Irregular QC.

Gender-stratified dose uniformity

Under Regular QC conditions, administered technetium-99 m doses were consistent between males and females. In Group 1 (MIBI), males received a mean of 750.40 MBq and females 746.21 MBq. In Group 2 (Myoview), males received 708.75 MBq and females 710.83 MBq. In contrast, Irregular QC groups showed slightly more variability—particularly Group 4 (Myoview), where males received 695.33 MBq and females 690.53 MBq. Overall, gender-based differences were minimal and not statistically significant. These values are summarized in Table 2.

Table 2.

Mean administered activity of technetium-99 m tracers by gender across four imaging groups. Regular QC maintained dosing consistency across sexes

Group	Radiopharmaceutical	QC Type	Gender	Mean Dose (MBq)
G1	MIBI	Regular	Male	750.40
G1	MIBI	Regular	Female	746.21
G2	Myoview	Regular	Male	708.75
G2	Myoview	Regular	Female	710.83
G3	MIBI	Irregular	Male	712.53
G3	MIBI	Irregular	Female	712.68
G4	Myoview	Irregular	Male	695.33
G4	Myoview	Irregular	Female	690.53

Age-stratified dose distribution

A comparison of administered activity between patients < 55 years and ≥ 55 years revealed stable dose distribution under Regular QC. For Group 1 (MIBI), younger patients received a mean dose of 745.27 MBq, while older patients received 749.39 MBq. Group 2 (Myoview) showed a similarly tight range with 706.09 MBq (< 55) and 711.65 MBq (≥ 55).

Under Irregular QC, dose variability increased slightly. Group 3 (MIBI) showed 707.30 MBq (< 55) and 714.83 MBq (≥ 55), and Group 4 (Myoview) reported 695.17 MBq (< 55) and 692.11 MBq (≥ 55). These results, outlined in Table 3, indicate that consistent QC practices minimize dosing variability across age groups.

Table 3.

Mean administered dose of technetium-99 m radiopharmaceuticals by age group in each imaging subgroup. Regular QC preserved dose consistency across age strata

Group	Radiopharmaceutical	QC Type	Age Group	Mean Dose (MBq)
G1	MIBI	Regular	< 55 years	745.27
G1	MIBI	Regular	≥ 55 years	749.39
G2	Myoview	Regular	< 55 years	706.09
G2	Myoview	Regular	≥ 55 years	711.65
G3	MIBI	Irregular	< 55 years	707.30
G3	MIBI	Irregular	≥ 55 years	714.83
G4	Myoview	Irregular	< 55 years	695.17
G4	Myoview	Irregular	≥ 55 years	692.11

Because only ectopic adenomas were included in this cohort, all ‘detected’ and ‘localized’ results below refer specifically to ectopic lesions confirmed by surgery.

Localization performance by QC and tracer

Localization performance also varied significantly across QC and tracer combinations. Group 1 (MIBI with Regular QC) achieved the highest localization accuracy (88.2%), followed by Group 2 (Myoview with Regular QC) at 70.6%. In contrast, Groups 3 and 4, which operated under Irregular QC, had substantially lower localization accuracy—29.4% and 23.5%, respectively. These results are summarized in Table 4, with detection performance by modality and tracer detailed in Table 5.

Table 4.

Localization performance of SPECT/CT for ectopic parathyroid adenomas stratified by tracer and QC group

Group	Tracer	QC Type	Ectopic Detected	Correctly Localized	Mislocalized or Ambiguous
G1	MIBI	Regular	34	30	4
G2	Myoview	Regular	34	24	10
G3	MIBI	Irregular	34	10	24
G4	Myoview	Irregular	34	8	26

Table 5.

Detection outcomes for SPECT/CT stratified by tracer and quality control condition

Section	Stratum	Detected	Total	Rate (%)
Overall	All	115	136	84.6
By tracer	MIBI	63	68	92.6
By tracer	Myoview	52	68	76.5
By QC	Regular QC	66	68	97.1
By QC	Irregular QC	49	68	72.1

Detection outcomes by QC

SPECT/CT demonstrated higher detection accuracy in patients imaged under Regular QC conditions compared to Irregular QC. The overall detection rate was 97.1% (66/68) for Regular QC and 72.1% (49/68) for Irregular QC, a statistically significant difference (χ² = 16.275, p < 0.001), as shown in Table 6.

Table 6.

Detection outcomes for SPECT/CT under regular and irregular QC conditions. QC adherence was a significant determinant of detection accuracy (χ²(1) = 16.275, p < 0.001)

QC Level	Not Detected (0)	Detected (1)	Total
Irregular (n = 68)	19	49	72.1%
Regular (n = 68)	2	66	97.1%
Total	21	115	84.6%

Figure 1 illustrates the detection accuracy of SPECT/CT and planar imaging under both Regular and Irregular QC conditions. SPECT/CT under Regular QC achieved the highest detection rates across all tracer conditions, while performance dropped significantly under Irregular QC—particularly for Myoview. Planar imaging showed consistently lower accuracy regardless of QC adherence, confirming the superior diagnostic yield of SPECT/CT when paired with robust quality control.

Fig. 1.

Detection accuracy (%) of SPECT/CT and planar imaging under regular and irregular QC conditions

Figure 2 shows the proportion of correctly localized ectopic adenomas based on QC adherence. Under Regular QC, 79% of surgically confirmed ectopic lesions were correctly localized, whereas under Irregular QC, only 21% of ectopic lesions were correctly localized. This highlights the critical role of quality control in ensuring anatomical precision during hybrid SPECT/CT imaging.

Fig. 2.

Proportion of correctly localized ectopic parathyroid adenomas (as surgically confirmed) by QC level

Tracer influence under varying QC

When stratified by tracer and QC condition, technetium-99 m sestamibi (MIBI) demonstrated superior resilience to quality control variability. Under Regular QC, MIBI achieved a 100% detection rate (Group 1), while Myoview yielded 94.1% (Group 2). Under Irregular QC, performance deteriorated across both tracers, but to different extents. MIBI retained an 85.3% detection rate in Group 3, despite a 70.6% localization error rate. In contrast, Myoview under Irregular QC (Group 4) showed only 58.8% detection, with localization errors reaching 76.5%. These results underscore that while both tracers perform acceptably under strict QC, MIBI is markedly more robust when QC protocols are inconsistently applied.

Planar vs. SPECT/CT

SPECT/CT was consistently superior to planar imaging across all diagnostic measures. As shown in Table 7, the overall detection rate using SPECT/CT was 84.6% (115/136), while planar imaging detected only 36.0% (49/136) of cases. Furthermore, Table 8 demonstrates that planar detection was not significantly influenced by tracer type—MIBI yielded 39.7% and Myoview 32.4% (χ² = 0.798, p = 0.372). These results reinforce that planar scintigraphy lacks the spatial resolution and anatomical correlation needed for reliable preoperative localization, making SPECT/CT the preferred imaging modality for parathyroid adenoma detection.

Table 7.

Comparison of overall detection and localization performance between SPECT/CT and planar imaging in a 136-patient cohort

Variable	Detected (1)	Not Detected (0)	Total Cases	Detection Rate (%)
SPECT/CT Detected	115	21	136	84.6
Planar Detected	49	87	136	36.0
Correct Localization	72	64	136	52.9
Surgery Confirmed	136	0	136	100.0

Table 8.

Planar imaging detection rates for MIBI and Myoview, showing minimal tracer influence without CT integration

Tracer	Not Detected (0)	Detected (1)	Total Cases
MIBI (n = 68)	41	27	39.7%
Myoview (n = 68)	46	22	32.4%
Total	87	49	72.1%

Discussion

In this 136-patient cohort, Regular QC produced both tighter administered-activity distributions and markedly higher diagnostic performance than Irregular QC. Mean doses were highest and most uniform in G1 (MIBI/Regular QC) and lowest in G4 (Myoview/Irregular QC) (Table 1), with stability preserved across sex and age under Regular QC (Tables 2 and 3). Diagnostically, SPECT/CT detection was 97.1% with Regular QC versus 72.1% with Irregular QC (Table 6), and localization accuracy fell steeply when QC lapsed (Table 4). These effects outweighed tracer choice alone: under Regular QC, both tracers performed well (MIBI 100%, Myoview 94.1%), but under Irregular QC Myoview showed a larger decline (58.8% detection; 76.5% localization errors) than MIBI (85.3% detection; 70.6% localization errors) (Table 9). Planar imaging remained uniformly inferior (36.0% detection) and insensitive to tracer (Tables 7 and 8).

Table 9.

Summary of tracer performance and quality control adherence across all four imaging groups, showing detection rates and localization accuracy

Group	QC Type	Tracer	Phantom Use	Dose Calibration	Ectopic Detected	Localization Errors
G1	Regular	MIBI	Daily	Verified	34	4
G2	Regular	Myoview	Daily	Verified	32	10
G3	Irregular	MIBI	Skipped	Occasional	29	24
G4	Irregular	Myoview	Rare	Unreliable	20	26

The step-change in both dose consistency and diagnostic yield between Regular and Irregular QC directly serves the study aim and title: QC adherence—not merely hardware capability—governs real-world SPECT/CT performance. Our Regular-QC strata (97.1% detection; higher localization) echo practice guidance that daily camera uniformity, dose-calibrator verification, and standardized acquisition/reconstruction are prerequisites for reproducible image quality and reliable fusion (Ovčariček et al. 2021). By contrast, Irregular QC likely introduced non-uniformity, centering/peaking drift, and protocol variability that reduce lesion-to-background contrast and increase misregistration—mechanisms consistent with QC-focused recommendations and with the broader emphasis on method discipline for accurate hybrid imaging (Morris et al. 2022, Ovčariček et al. 2021).

The tracer analysis addresses the second component of the study aim. Under standardized conditions, MIBI and Myoview achieved high detection, aligning with reports that both lipophilic cationic tracers can localize hyperfunctioning tissue when protocols are optimized [1–2]. However, when QC was irregular, Myoview degraded more than MIBI. This pattern coheres with pharmacokinetic differences: MIBI’s slower washout and stronger mitochondrial retention sustain target-to-background contrast across dual-phase imaging, whereas tetrofosmin’s faster clearance is more timing-sensitive and thus more vulnerable to any protocol drift (Giordano et al. 2003). Our data quantify that vulnerability, showing a sharper drop in both detection and localization for Myoview when QC was inconsistent.

The tighter administered-activity distributions observed under Regular QC—across tracer, sex, and age (Tables 1, 2 and 3)—directly support dose optimization and local DRL work. Stable, traceable activity administration is a foundational requirement for establishing and auditing DRLs across institutions; QC variability, by contrast, propagates as wider dose dispersion and undermines comparability (Dennis et al. 2018). Our results empirically connect routine QC with both clinical accuracy and dosimetric discipline, reinforcing the operational link between quality assurance and radiation protection aims (Ovčariček et al. 2021, Dennis et al. 2018).

Consistent with the clinical role of SPECT/CT in preoperative localization (Morris et al. 2022), our paired comparisons show clear superiority of SPECT/CT over planar imaging for detection and anatomical mapping (Tables 7 and 8; Figs. 1 and 2). The incremental value of attenuation correction, 3D localization, and CT-based correlation explains the higher detection and localization we observed—particularly for anatomically challenging or ectopic disease—where planar techniques underperform (Morris et al. 2022).

For departments seeking immediate, measurable gains, the highest-leverage actions are: (i) enforce daily camera uniformity/peaking and dose-calibrator constancy; (ii) lock acquisition and reconstruction parameters; (iii) document QC pass/fail, injected activity, timing, motion, and fusion quality in the report; and (iv) audit detection/localization key performance indicators (KPIs) against QC compliance. Where both tracers are available, MIBI is preferable for dual-phase protocols in settings where QC variability cannot be fully controlled, given its demonstrated resilience in our Irregular-QC strata (Spanu et al. 2014, Giordano et al. 2003).

Conclusion

Regular quality control emerged as the dominant determinant of diagnostic performance and localization reliability in parathyroid SPECT/CT imaging. Consistent QC practices ensured stable administered activity and reliable lesion localization, whereas lapses in QC were associated with reduced diagnostic confidence. While both technetium-99 m sestamibi and tetrofosmin performed well under standardized conditions, sestamibi demonstrated greater robustness when QC adherence was inconsistent. Planar imaging remained inferior to SPECT/CT for both detection and anatomical localization. These findings emphasize the central role of QC standardization and protocol consistency in optimizing SPECT/CT outcomes and support the continued use of SPECT/CT as the primary imaging modality for preoperative parathyroid localization.

Author contributions

Badriah Alasmari: Concept and study design; data acquisition; data analysis and interpretation; manuscript drafting; final approval; guarantor of the work. Reham Salah El-Din Sherif: Academic supervision; study design; imaging and statistical interpretation; critical manuscript review; final approval. Magdy Mohamed Ghannam: Principal academic supervisor; methodology; oversight of analysis and interpretation; critical review; final approval; guarantor of the work. Khalid Elsaban: Clinical supervision; verification of imaging protocols and QC procedures; clinical data validation; critical review; final approval. Mohammed Abdullah Al-Amri: Data acquisition; technical support; retrieval of imaging/QC records; manuscript review; final approval.

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Data availability

The datasets generated and analysed during this study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

This retrospective study was conducted in accordance with the Declaration of Helsinki. Ethical approval was obtained from the Hospital Research Ethics Committee, Al-Hada Armed Forces Hospital, Taif Region, Ministry of Defense(Reg. No. H-02-T-078, REC No. 2025 − 1085, Approval date: 24 June 2025). Owing to the retrospective nature of the study, the requirement for written informed consent was waived.

Consent to participate

Informed consent was waived by the Hospital Research Ethics Committee due to the retrospective design and use of anonymized clinical data.

Consent to publish

Not applicable; no identifiable patient images or personal data are included.

Reporting guideline

The study was designed and reported in accordance with the STARD (Standards for Reporting Diagnostic Accuracy Studies) guidelines.

Competing interests

The authors declare that they have no competing financial or non-financial interests.