Many elegant inorganic designs have been developed to aid medical imaging. We know better now how to improve imaging due to the enormous efforts made by scientists in probe design and other fundamental sciences, including inorganic chemistry, physiochemistry, analytical chemistry, and biomedical engineering. However, despite several years being invested in the development of diagnostic probes, only a few examples have shown applicability in MRI in vivo. In this short review, we aim to show the reader the latest advances in the application of inorganic agents in preclinical MRI.

Paramagnetic metal ion complexes, mostly based on gadolinium (Gd³⁺), have been used for over 30 years as magnetic resonance imaging (MRI) contrast agents. Gd³⁺-based contrast agents have a strong influence on T₁ relaxation times and are consequently the most commonly used agents in both the clinical and research environments. Zinc is an essential element involved with over 3000 different cellular proteins, and disturbances in tissue levels of zinc have been linked to a wide range of pathologies, including Alzheimer’s disease, prostate cancer, and diabetes mellitus. MR contrast agents that respond to the presence of Zn²⁺ in vivo offer the possibility of imaging changes in Zn²⁺ levels in real-time with the superior spatial resolution offered by MRI. Such responsive agents, often referred to as smart agents, are typically composed of a paramagnetic metal ion with a ligand encapsulating it and one or more chelating units that selectively bind with the analyte of interest. Translation of these agents into clinical radiology is the next goal. In this review, we discuss Gd³⁺-based MR contrast agents that respond to a change in local Zn²⁺ concentration.

Dual-energy CT (DECT) has been available for clinical use since 2006. Since its clinical debut, multiple different dual-energy systems have been developed including sequential acquisition, rapid-switching, dual-source, and twin-beam, in addition to spectral imaging techniques such as dual-layer and photon counting CT. While the specifics of these techniques vary, the underlying principles remain the same; by acquiring at least 2 datasets, material-specific information in each image voxel can be determined. Most commonly used to evaluate for the presence or absence of iodine, DECT has found clinical applications in the assessment of gastrointestinal bleeding, bone marrow oedema, the characterization of renal stones, and the accurate evaluation of vascular stenosis, among other uses. This review aims to familiarize the radiologist with the theoretical basis underlying DECT, describe the different types of DECT including the relative strengths and weaknesses of each, and highlight specific clinical applications for which DECT may be valuable.

Prostate cancer (PCa) will affect approximately 12% of US men in their lifetime and remains the 2nd most common cause of cancer-specific death. However, there is a broad spectrum of severity of PCa; some require aggressive treatment and others can “watch-and-wait”. Distinction of clinically significant prostate cancer (csPCa) from indolent PCA with current imaging methods remains challenging. This study aims to evaluate dynamic prostate specific membrane antigen (PSMA) positron emission tomography (PET/CT) in the characterization of suspicious prostate lesions identified on multiparametric MRI (mpMRI). Prospective study of biopsy-naïve patients with at least one Prostate Imaging and Reporting Data System (PI-RADS) score 5 or one PI-RADS score 4 plus a prostate specific antigen (PSA) ≥ 10 ng/mL. Dynamic PET/CT was performed for 30 min after administration of 68Ga Gozetide. Time activity curves (TAC; kBq/cc) of suspicious prostate lesions were generated. TAC logarithmic slope was calculated for each GG at 5-, 10-, 15-, and 30 min. Apparent diffusion coefficient (ADC) at mpMRI for each lesion was tabulated. 19 PI-RADS v2.1 ≥ 4 and 6 secondary PI-RADS v2.1 ≥ 3 lesions in 19 patients were analyzed: 4 (16.0%) grade group (GG) 0 (benign), 3 (12.0%) GG 1, 6 (24.0%) GG 2, 6 (24.0%) GG 3, and 6 (24.0%) GG ≥ 4. Significant differences in slope values were observed between clinically insignificant disease (GG 0/1) and GG 2 or higher as early as 5 min post-injection (p < 0.05). At 30 min, GG 1 had the lowest mean slope (− 0.18 ± 0.57) and GG ≥ 4 exhibited the highest mean slope (2.35 ± 2.03). Slope value/ADC ratio further improved discrimination between different GGs. Dynamic 68 Ga Gozetotide time activity curves could distinguish GG0/1 from GG3 and GG4/5 PCa. The addition of mpMRI characteristics could further distinguish GG2 from GG4/5. GG2 could not be distinguished from GG3, probably due to small sample size. Clinical Implications. Dynamic 68 Ga Gozetotide PET/CT imaging may offer enhanced discrimination of MRI-visible prostate cancer lesions and assist in management decisions. Study registered with the FDA (IND 144,177) and clinicaltrials.gov (NCT04179968).