Let’s embrace optical imaging: a growing branch on the clinical molecular imaging tree

Abstract

Nuclear medicine first became recognised as a potential medical speciality in the early 1950s of the last century when Seidlin reported on the success of radioactive iodine (I-131) in treating a patient with advanced thyroid cancer [1, 2]. The use of the rectilinear scanner contributed to the widespread clinical use of diagnostic nuclear medicine and resulted in planar, somewhat spotty images which constituted of plotted dots [3]. Importantly, this methodology already acted on the tracer principle, i.e. the use of a radioactive compound (radiopharmaceutical) to visualise in vivo processes and to reveal physiological and pathophysiological changes. In those days, nuclear medicine often served as an alternative approach or an add-on tool to the radiological morphological imaging techniques [4]. Demonstrating, for example, a blood–brain barrier disruption using brain diethylenetriaminepentaacetic acid (DTPA) scans as a sign for a possible brain tumour was certainly — at the time — less invasive when compared to the radiological pneumoventriculography, which used air injected in the ventricular system as an indirect contrast for adjacent brain tumours. 99mTc colloid liver scans, for example, added to the detection of hepatic defects in case of primary liver tumours or liver metastases [5]. Due to the clinical breakthroughs over the following decades in radiology, in computed tomography (CT) and in magnetic resonance imaging (MRI) with increasing resolution and accuracy, the clinical dissemination of these imaging techniques was rapid. In addition, this development resulted in a reduction of the nuclear medicine scans of the aforementioned type. In parallel, nuclear medicine itself as an imaging field saw the development of single-photon emission computed tomography (SPECT) [6] and positron emission tomography (PET) [7, 8] imaging modalities, benefitting from the ever-increasing computation power and continuous improvements in hardware detection systems, such as new crystals and digital detectors [6, 9, 10]. The clinical deployment of SPECT was boosted by the availability and development of 99mTc generators and pharmaceutical kits [11], allowing more efficient and cost-effective in-house institutional radiopharmaceutical labelling. Similarly, clinical PET imaging This article is part of the Topical Collection on Editorial