Quantitative application of dual-phase 99mTc-sestamibi SPECT/CT imaging of parathyroid lesions: identification of optimal timing in secondary hyperparathyroidism

Abstract

Purpose: In this retrospective study, we compared the maximum standardized uptake values (SUVmax) of parathyroid lesions and the target-to-background ratio (TBR) of parathyroid lesions to thyroid tissue in early-phase single-photon emission computed tomography/computed tomography (SPECT/CT) versus delayed-phase SPECT/CT in patients with secondary hyperparathyroidism (SHPT) in order to determine the optimal timing of 99mTc- methoxyisobutylisonitrile (99mTc-MIBI) SPECT/CT imaging.

Methods: Seventeen patients with a history of chronic kidney failure stage 5 on hemodialysis, underwent pre-operative parathyroid scintigraphy for detection and localization of parathyroid lesions. Retrospective analysis was conducted for lesions with focal accumulation of 99mTc-MIBI. All patients underwent dual-phase 99mTc-MIBI parathyroid scintigraphy and dual-phase SPECT/CT. SUVmax of parathyroid lesions and thyroid tissues was measured.

Results: Mean SUVmax of parathyroid lesions was 4.86 on early-phase and 2.58 on delayed-phase SPECT/CT, respectively. Mean TBR was 1.14 on early phase and 1.48 on delayed-phase SPECT/CT, respectively. Statistically significant differences in SUVmax and TBR between dual-phase SPECT/CT were observed (P < 0.001).

Conclusions: Delayed-phase SPECT/CT in SHPT is required because of the better image contrast.

Keywords: 99mTc-MIBI; Chronic kidney disease; Hyperparathyroidism; Maximum standardized uptake; SPECT/CT.

Fig. 1

SUVmax values of parathyroid lesions and both thyroid lobes in early-phase and in delayed-phase images. Median SUVmax of parathyroid lesions in early phase was 4.86, which was higher than both thyroid lobes without significant differences. Median SUVmax of parathyroid lesions in delayed phase was 2.58, which was higher than in both thyroid lobes, the differences being statistically significant (both P < 0.001)

Fig. 2

SUVmax changes in early and delayed phase in parathyroid lesions and both thyroid lobes. Boxplots indicate median value (black line), first and third quartile ranges (box). The SUVmax of both parathyroid lesions (left) and thyroid dual lobes (middle, thyroid left lobe; right, thyroid right lobe) in early phase was higher than in delayed phase with significant differences. Rank-sum testing for paired samples used for the difference between two phases in parathyroid lesions and thyroid dual lobes. All the differences were statistically significant (P < 0.001)

Fig. 3

Violin plot analysis comparing the TBR of parathyroid lesions in early-phase and delayed-phase images. The green group represents the early phase, whereas the orange represents the delayed phase. The red oval indicates the median value, while the size of the black box indicates the first and third quartile ranges. The rank-sum test of independent samples was used, and the TBR level in the delayed phase was significantly higher than in the early phase (P < 0.001). TBR is the tumor-to-background counts ratio

Fig. 4

Early phase of coronal SPECT (A), coronal CT (B), coronal SPECT/CT (C) and MIP (D) images from 99mTc-MIBI displaying a clear thyroid image (dotted arrow), with focal imaging agent concentration below the inferior pole of the left lobe (arrow). Delayed phase of coronal SPECT (E), coronal CT (F), coronal SPECT/CT (G) and MIP (H) images showed significant tracer washout from the thyroid (dotted arrow) while high concentration persisted in the lesion below the inferior pole of its left lobe (arrow). MIP is maximum intensity projection

Fig. 5

Correlations of TBR and SUVmax with serum biochemistry. The only factor significantly associated with TBR was parathyroid lesion SUVmax. The correlation tests between other factors and TBR showed no statistical significance