Impact of image fusion and attenuation correction by SPECT-CT on the scintigraphic detection of parathyroid adenomas

Summary

Aim: In addition to planar parathyroid scintigraphy, SPECT and image fusion with CT/MR improve adenoma detection in primary hyperparathyroidism (pHPT). This study evaluated the use of a hybrid SPECT-CT device concerning image fusion and attenuation correction (AC). Patients, methods: The data of 26 patients with pHPT, preoperatively examined by ^99mTc-sestamibi dual-phase scintigraphy plus SPECT-CT (low-dose CT), was retrospectively evaluated by two observers in a consensus reading. The images of planar scintigraphy, non-attenuation corrected SPECT (SPECTN_AC), attenuation corrected SPECT (SPECT_AC) and SPECT_AC-CT were interpreted and compared to the results of surgery. The effect of AC on focus intensity was semiquantified by determination of the tumor-to-background (TB) ratio for SPECT_AC and SPECTN_AC. Finally, the TB_AC/TB_NAC-ratio was calculated for each focus and correlated to the distance of a focus from the body surface. Results: 20/26 (77%) patients were positive in planar scintigraphy. One focus was detected by SPECT only. AC of SPECT-data increased image contrast but had no impact on the detection rate. Additional SPECT_AC-CT image fusion facilitated the localization of three mediastinal foci. In the semiquantitative analysis an increase in TB after AC was observed, although there was no strong correlation between depth of the focus (16-60 mm) and the TB_AC/TB_NAC-ratio (r = 0.213, p = 0.353). Conclusion: The detection rate of planar scintigraphy is only slightly improved by SPECT imaging. Due to the low spatial resolution of the CT component, the benefit of image fusion is limited to mediastinal foci. However, as TB and image contrast is measurably improved after AC there is a potential to improve the sensitivity of parathyroid SPECT.

Zusammenfassung

Ziel: Der Einsatz SPECT und Bildfusion mit CT/MRT erhöht die Detektionsrate von Adenomen der Nebenschilddrüsen (NSD) bei primärem Hyperparathyroidismus (pHPT). Diese Studie bewertete den Nutzen eines Hybrid-SPECT-CT-Geräts bezüglich Bildfusion und Schwächungskorrektur (AC). Patienten, Methoden: Die Daten von 26 pHPT-Patienten, die präoperativ mittels ^99mTc-Sestamibi-Zwei-Phasen-Szintigraphie und SPECT-CT (low-dose CT) untersucht worden waren, wurden von zwei Untersuchern retrospektiv im Konsens ausgewertet. Die planare Szintigraphie, die nicht-schwächungskorrigierte SPECT (SPECT_NAC), die schwächungskorrigierten SPECT (SPECT_AC) und die SPECT_AC-CT wurden reevaluiert und mit den chirurgischen Ergebnissen verglichen. Der Einfluss der AC auf die Fokusintensität wurde mittels Tumor- to-Background(TB)-Ratio für die SPECT_AC und die SPECT_NAC semiquantifiziert. Die TB_AC/TB_NAC-Quotient wurde für jeden Fokus ermittelt und mit dem Abstand des Herdes zur Körperoberfläche korreliert. Ergebnisse: 20/26 (77%) Patienten waren in der planaren Szintigraphie positiv. Ein Fokus wurde nur durch SPECT entdeckt. Die AC der SPECTDaten verbesserte den Bildkontrast aber hatte keinen Einfluss auf die Detektionsrate. Die zusätzliche SPECT_AC-CTBildfusion erleichterte die Lokalisierung dreier mediastinaler Foki. In der semiquantitativen Analyse wurde ein TB-Anstieg nach AC beobachtet, obwohl keine starke Korrelation zwischen Fokustiefe (16-60 mm) und der TB_AC/TB_NAC-Ratio (r = 0,213, p = 0,353) bestand. Schlussfolgerung: Die Detektionsrate der planaren NSD-Szintigraphie wird durch den SPECT-Einsatz nur geringfügig verbessert. Aufgrund der geringen Ortsauflösung der CT-Komponente ist die Bildfusion nur bei mediastinalen Foki von Vorteil. Da TB und Bildkontrast nach AC verbessert werden, besteht hier ein Potenzial zur Sensitivitätssteigerung der SPECT.

Keywords

SPECT - attenuation correction - parathyroid scintigraphy - primary hyperparathyroidism - image fusion

Schlüsselwörter

SPECT - Schwächungskorrektur - Nebenschilddräsenszintigraphie - primärer Hyperparathyroidismus - Bildfusion

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