Imaging Hepatocellular Carcinoma With 68Ga-Citrate PET: First Clinical Experience

Drug-tolerant persister cells in cancer: the cutting edges and future directions

Drug-tolerant persister (DTP) cell populations were originally discovered in antibiotic-resistant bacterial biofilms. Similar populations with comparable features have since been identified among cancer cells and have been linked with treatment resistance that lacks an underlying genomic alteration. Research over the past decade has improved our understanding of the biological roles of DTP cells in cancer, although clinical knowledge of the role of these cells in treatment resistance remains limited. Nonetheless, targeting this population is anticipated to provide new treatment opportunities. In this Perspective, we aim to provide a clear definition of the DTP phenotype, discuss the underlying characteristics of these cells, their biomarkers and vulnerabilities, and encourage further research on DTP cells that might improve our understanding and enable the development of more effective anticancer therapies.

The Evaluation of 68Ga-Citrate PET/CT Imaging for Dihydroartemisinin in the Treatment of Rheumatoid Arthritis

PURPOSE

We aimed to use 68Ga-citrate, a labeled product of gallium (iron analog), combined with positron emission tomography/computed tomography (PET/CT) to non-invasively evaluate the potential of the iron-responsive product dihydroartemisinin (DHA) in the treatment of rheumatoid arthritis.

PROCEDURES

From the establishment of chicken II collagen-induced arthritis (CIA) rat model over 40 days, 20 rats with one-to-one corresponding arthritis index (AI) scores were randomly divided into two groups. One group received oral DHA (at a dose of 1.5 ml/(kg day), containing 20 mg DHA per 1 ml) for 15 days; the other group received stroke-physiological saline solution (SSS, 1.5 ml/(kg day) for 15 days. 68Ga-citrate micro-PET/CT imaging was performed on day 0 (D0), day 5 (D5), day 10 (D10), and day 15 (D15) of oral administration. After data reconstruction, the cross-sectional length "d" of the ankle joint of each rat was measured on the transverse CT, and the SUVmax of the ankle joint and muscle background was measured for statistical analysis. After micro-PET/CT collection, the ankle joint tissue was observed by HE staining.

RESULTS

The ankle joint swelling in the DHA group was significantly suppressed, but the SSS group showed no significant suppression. 68Ga-citrate micro-PET/CT imaging results and microscope observation confirmed this finding. Statistical analysis indicated that the time tendency of AI score (Binteraction = 0.495, P < 0.001) and T/NT (Binteraction = 1.345, P < 0.001) were discrepant between DHA and SSS groups. The AI score and T/NT of the DHA group gradually increased with time, while the SSS group score gradually decreased. Furthermore, the Spearman correlation coefficient was used to describe the relationship between "d" and T/NT, which was positively correlated (r = 0.855, P < 0.001).

CONCLUSIONS

This study showed that the anti-inflammatory effect of the iron-responsive product DHA in arthritis can be monitored by an iron-like radioactive tracer (68Ga-citrate).

Quantitative and Qualitative Improvement of Low-Count [68Ga]Citrate and [90Y]Microspheres PET Image Reconstructions Using Block Sequential Regularized Expectation Maximization Algorithm

PURPOSE

There are several important positron emission tomography (PET) imaging scenarios that require imaging with very low photon statistics, for which both quantitative accuracy and visual quality should not be neglected. For example, PET imaging with the low photon statistics is closely related to active efforts to significantly reduce radiation exposure from radiopharmaceuticals. We investigated two examples of low-count PET imaging: (a) imaging [⁹⁰Y]microsphere radioembolization that suffers the very small positron emission fraction of Y-90's decay processes, and (b) cancer imaging with [⁶⁸Ga]citrate with uptake time of 3-4 half-lives, necessary for visualizing tumors. In particular, we investigated a type of penalized likelihood reconstruction algorithm, block sequential regularized expectation maximization (BSREM), for improving both image quality and quantitative accuracy of these low-count PET imaging cases.

PROCEDURES

The NEMA/IEC Body phantom filled with aqueous solution of Y-90 or Ga-68 was scanned to mimic the low-count scenarios of corresponding patient data acquisitions on a time-of-flight (TOF) PET/magnetic resonance imaging system. Contrast recovery, background variation, and signal-to-noise ratio were evaluated in different sets of count densities using both conventional TOF ordered subset expectation (TOF-OSEM) and TOF-BSREM algorithms. The regularization parameter, beta, in BSREM that controls the tradeoff between image noise and resolution was evaluated to find a value for improved confidence in image interpretation. Visual quality assessment of the images obtained from patients administered with [⁶⁸Ga]citrate (n = 6) was performed. We also made preliminary visual image quality assessment for one patient with [⁹⁰Y]microspheres. In Y-90 imaging, the effect of 511-keV energy window selection for minimizing the number of random events was also evaluated.

RESULTS

Quantitatively, phantom images reconstructed with TOF-BSREM showed improved contrast recovery, background variation, and signal-to-noise ratio values over images reconstructed with TOF-OSEM. Both phantom and patient studies of delayed imaging of [⁶⁸Ga]citrate show that TOF-BSREM with beta = 500 gives the best tradeoff between image noise and image resolution based on visual assessment by the readers. The NEMA-IQ phantom study with [⁹⁰Y]microspheres shows that the narrow energy window (460-562 keV) recovers activity concentrations in small spheres better than the regular energy window (425-650 keV) with the beta value of 2000 using the TOF-BSREM algorithm. For the images obtained from patients with [⁶⁸Ga]citrate using TOF-BSREM with beta = 500, the visual analogue scale (VAS) was improved by 17 % and the Likert score was increased by 1 point on average, both in comparison to corresponding scores for images reconstructed using TOF-OSEM.

CONCLUSION

Our investigation shows that the TOF-BSREM algorithm improves the image quality and quantitative accuracy in low-count PET imaging scenarios. However, the beta value in this algorithm needed to be adjusted for each radiopharmaceutical and counting statistics at the time of scans.

Metal-Based Complexes as Pharmaceuticals for Molecular Imaging of the Liver

This article reviews the use of metal complexes as contrast agents (CA) and radiopharmaceuticals for the anatomical and functional imaging of the liver. The main focus was on two established imaging modalities: magnetic resonance imaging (MRI) and nuclear medicine, the latter including scintigraphy and positron emission tomography (PET). The review provides an overview on approved pharmaceuticals like Gd-based CA and ^99mTc-based radiometal complexes, and also on novel agents such as ⁶⁸Ga-based PET tracers. Metal complexes are presented by their imaging modality, with subsections focusing on their structure and mode of action. Uptake mechanisms, metabolism, and specificity are presented, in context with advantages and limitations of the diagnostic application and taking into account the respective imaging technique.

Targeting iron metabolism in high-grade glioma with 68Ga-citrate PET/MR

Noninvasive tools that target tumor cells could improve the management of glioma. Cancer generally has a high demand for Fe(III), an essential nutrient for a variety of biochemical processes. We tested whether 68Ga-citrate, an Fe(III) biomimetic that binds to apo-transferrin in blood, detects glioma in preclinical models and patients using hybrid PET/MRI. Mouse PET/CT studies showed that 68Ga-citrate accumulates in subcutaneous U87MG xenografts in a transferrin receptor-dependent fashion within 4 hours after injection. Seventeen patients with WHO grade III or IV glioma received 3.7-10.2 mCi 68Ga-citrate and were imaged with PET/MR 123-307 minutes after injection to establish that the radiotracer can localize to human tumors. Multiple contrast-enhancing lesions were PET avid, and tumor to adjacent normal white matter ratios were consistently greater than 10:1. Several contrast-enhancing lesions were not PET avid. One minimally enhancing lesion and another tumor with significantly reduced enhancement following bevacizumab therapy were PET avid. Advanced MR imaging analysis of one patient with contrast-enhancing glioblastoma showed that metabolic hallmarks of viable tumor spatially overlaid with 68Ga-citrate accumulation. These early data underscore that high-grade glioma may be detectable with a radiotracer that targets Fe(III) transport.