*Review* **Absolute Quantification in Diagnostic SPECT/CT: The Phantom Premise**

**Stijn De Schepper 1,2,\*, Gopinath Gnanasegaran 3, John C. Dickson 4 and Tim Van den Wyngaert 1,2**


**Abstract:** The application of absolute quantification in SPECT/CT has seen increased interest in the context of radionuclide therapies where patient-specific dosimetry is a requirement within the European Union (EU) legislation. However, the translation of this technique to diagnostic nuclear medicine outside this setting is rather slow. Clinical research has, in some examples, already shown an association between imaging metrics and clinical diagnosis, but the applications, in general, lack proper validation because of the absence of a ground truth measurement. Meanwhile, additive manufacturing or 3D printing has seen rapid improvements, increasing its uptake in medical imaging. Three-dimensional printed phantoms have already made a significant impact on quantitative imaging, a trend that is likely to increase in the future. In this review, we summarize the data of recent literature to underpin our premise that the validation of diagnostic applications in nuclear medicine using application-specific phantoms is within reach given the current state-of-the-art in additive manufacturing or 3D printing.

**Keywords:** absolute quantification; SPECT/CT; phantoms; diagnostics; 3D printing
