Detection of parathyroid adenomas with 4DCT: Towards a true four-dimensional technique

Abstract

\n Background. 4DCT is a commonly performed examination in the management of primary hyperparathyroidism, combining three-dimensional imaging with enhancement over time as the fourth dimension. We propose a novel technique consisting of 16 different contrast phases, instead of three or four different phases. The main aim of this study was to see if this protocol allows for the detection of parathyroid adenomas within dose limits. Our secondary aim was examining the enhancement of parathyroid lesions over time.Methods. For this prospective study, we included 15 patients with primary hyperparathyroidism prior to surgery. We obtain a 4DCT with 16 different phases: an unenhanced phase followed by 11 consecutive arterial phases and 4 venous phases. Centered on the thyroid, continuous axial scanning is performed over a fixed 8cm or 16cm coverage volume after start of contrast administration.Results. In all patients an enlarged parathyroid can be demonstrated, mean lesion size is 13.6mm. Mean peak arterial peak enhancement for parathyroid lesions is 384 HU compared to 333 HU for the normal thyroid. No statistical difference could be found. Time to peak (TTP) is significantly earlier for parathyroid adenomas compared to normal thyroid tissue: 30.8s versus 32.3s (p value 0.008). Mean Slope of Increase (MSI) of the enhancement curve is significantly steeper compared to normal thyroid tissue: 29.8% versus 22.2% (p value 0.012). Mean dose length product was 890.7 mGy.cm with a calculated effective dose of 6.7 mSv.Conclusion. We propose a feasible 4DCT scanning-protocol for the detection of parathyroid adenomas. We manage to obtain a multitude of phases, allowing for a dynamic evaluation within an acceptable exposure range when compared to classic helical 4DCT. Our 4DCT protocol may allow for a better visualization of the pattern of enhancement of parathyroid lesions, as enhancement over time curves can be drawn. This way wash-in and wash-out of contrast in suspected lesions can be readily demonstrated. Motion artifacts are less problematic as multiple phases are available.