Navigating beyond the 6th dimension: a challenge in the era of multi-parametric molecular imaging

This is an exciting time for molecular imaging as we are witnessing a convergence and combination of various imaging modalities driven by an unprecedented multidisciplinary collaboration between scientists. A consequence of this growth is a paradigm shift in health care delivery that is now revolutionizing clinical practice. Within the spectrum of macroscopic medical imaging, sensitivity ranges from the detection of millimolar to submillimolar concentrations of contrast media with computed tomography (CT) and magnetic resonance imaging (MRI), respectively, to picomolar concentrations in positron emission tomography (PET): a 10–10 difference [1]. Despite the remarkable progress and outstanding scientific innovations achieved and the much worthwhile successful research carried out both in academic and corporate settings, there are still plenty of open research questions that offer ample opportunities for the new generation of molecular imaging scientists [2]. There is no shortage of challenges and opportunities nowadays for developing novel molecular imaging probes and technologies and for establishing their role through innovative applications in clinical and research settings. The only limit is the imagination and creativity of the investigators and the challenge is the ability of opinion leaders to attract the best scientists into this discipline. It is the responsibility of scientists involved in today’s molecular imaging research enterprise to debate about essential issues related to the relevance of novel technologies with the aim of focusing the limited resources available for the best benefit of our community. In this respect, the issue of whether the development of molecular imaging technologies should be driven by fundamental molecular biology or design engineering was raised recently [3] and is still a matter of debate [4]. What our community has learned and accepted as a fact dictated by the unremitting modernization of our profession is that medical physicists must either learn to include the biology of molecular imaging in their research programmes or prepare to become irrelevant to the future of this discipline [3]. Among many other issues, the important role of multimodality imaging is growing steadily and gaining acceptance both in the clinical setting [5] and experimental preclinical studies [6]. As diagnostic techniques transition from the systems to the molecular level, the role of multimodality imaging becomes ever more important. Multimodality imaging with high spatial resolution and good sensitivity, allowing one to combine modalities and record either sequentially or simultaneously complementary information gathered from SPECT, PET, CT, MRI, ultrasound (US), optical imaging (OI), fluorescence and bioluminescence imaging, offers many advantages in certain research experiments. MRI, US and CT are favourably suited to assess perfusion, relative blood volume and vessel permeability and as such functional data derived from these imaging modalities may be combined with molecular information provided by SPECT and PET. Optical imaging is a very sensitive biological imaging technique to examine gene expression due to the very low background light levels [7]. Its capability to probe very small signals allows visualization of early expression and signal changes compared to PET imaging. However, PET is a quantitative modality that can provide measurements of metabolic function. While virtually all commercially available clinical and hybrid imaging systems have been configured in the form of SPECT/CT [8] or PET/CT [9], combined PET/MR scanners [10, 11] allowing for simultaneous (as opposed to sequential Eur J Nucl Med Mol Imaging (2009) 36:1025–1028 DOI 10.1007/s00259-009-1095-z