Molecular imaging of angiogenesis with SPECT

Single-photon emission computed tomography (SPECT) and position emission tomography (PET) are the two main imaging modalities in nuclear medicine. SPECT imaging is more widely available than PET imaging and the radionuclides used for SPECT are easier to prepare and usually have a longer half-life than those used for PET. In addition, SPECT is a less expensive technique than PET. Commonly used gamma emitters are: 99mTc (Emax 141 keV, T1/2 6.02 h), 123I (Emax 529 keV, T1/2 13.0 h) and 111In (Emax 245 keV, T1/2 67.2 h). Compared to clinical SPECT, PET has a higher spatial resolution and the possibility to more accurately estimate the in vivo concentration of a tracer. In preclinical imaging, the situation is quite different. The resolution of microSPECT cameras (<0.5 mm) is higher than that of microPET cameras (>1.5 mm). In this report, studies on new radiolabelled tracers for SPECT imaging of angiogenesis in tumours are reviewed

18F-Fluciclovine PET/CT performance in biochemical recurrence of prostate cancer: a systematic review

Background A systematic literature review of the performance of 18Fluorine-fluciclovine PET/CT for imaging of men with recurrent prostate cancer was performed. Methods Scientific literature databases (MEDLINE, ScienceDirect and Cochrane Libraries) were searched systematically during Oct 2020 using PRISMA criteria. No limit was put on the date of publication. Prospective studies reporting a patient-level 18F-fluciclovine detection rate (DR) from ≥25 patients with recurrent prostate cancer were sought. Proceedings of relevant meetings held from 2018 through Oct 2020 were searched for abstracts meeting criteria. Results Searches identified 321 unique articles. In total, nine articles (six papers and three conference abstracts), comprising a total of 850 patients met inclusion criteria. Most studies (n = 6) relied on ASTRO-Phoenix Criteria, EAU-ESTRO-SIOG, and/or ASTRO-AUA guidelines to identify patients with biochemical recurrence. Patients’ PSA levels ranged from 0.02–301.7 ng/mL (median level per study, 0.34–4.10 ng/mL [n = 8]). Approximately 64% of patients had undergone prostatectomy, but three studies focused solely on post-prostatectomy patients. Adherence to imaging protocol guidelines was heterogeneous, with variance seen in administered activity, uptake and scan times. Overall patient-level DR varied between studies from 26% to 83%, with 78% of studies reporting a DR > 50%. DR was proportional to PSA, but even at PSA < 0.5 ng/mL DR of up to 53% were reported. Prostate/bed DR (n = 7) ranged from 18% to 78% and extra-prostatic rates (n = 6) from 8% to 72%. Pelvic node and bone lesion DR ranged from 8% to 47% and 0% to 26%, respectively (n = 5). 18F-Fluciclovine PET/CT was shown to impact patient management and outcomes. Two studies reported 59–63% of patients to have a management change post-scan. A further study showed significant increase in failure-free survival following 18F-fluciclovine-guided compared with conventional imaging-guided radiotherapy planning. Conclusions 18F-Fluciclovine PET/CT shows good performance in patients with recurrent prostate cancer leading to measurable clinical benefits. Careful adherence to recommended imaging protocols may help optimize DR

Signal alterations, artifacts and image distortion induced by a superparamagnetic contrast medium. A phantom study in a 0.3 tesla MR system

In a phantom study using a 0.3 tesla MR system the signal alterations, artifacts and image distortion induced by a bowel contrast medium containing superparamagnetic magnetite particles were evaluated. A concentration of 20 mg iron/l was most useful because it caused a significant signal reduction without disturbing artifacts and image distortion. The signal reduction was most pronounced on long TR/TE spin echo sequences. The appearance and distribution of artifacts are related to the direction of the static magnetic field and frequency encoding gradient. The size of artifacts is related to the concentration of the contrast medium and the band width used

MR imaging of the pancreas at 0.3 T using a super-paramagnetic oral contrast medium

Twenty patients with carcinoma of the pancreas identified with ultrasonography and/or CT and confirmed by histology, were examined with MR before and after administration of an oral super-paramagnetic contrast medium. Ten patients were examined after administration of the contrast medium through a duodenal tube. Ten patients drank the contrast medium mixed with a viscosity-increasing agent. Organ delineation and diagnostic information were improved in the postcontrast scans in both groups and the viscous contrast suspension yielded better delineation and diagnostic information than the aqueous suspension. The viscous contrast suspension also showed better tolerance, contrast distribution and less artifacts than the aqueous suspension

Motion associated susceptibility artifacts

A bowel labeling agent is important for improving abdominal MR. Besides providing contrast between the bowel and other organs, the contrast agent itself is a potential source of artifacts. The artifacts created by superparamagnetic particles (SPP) subjected to motion have been studied in vitro at 0.5 T, and compared to artifacts created by a paramagnetic compound. Apart from the expected static effects of the SPP, movement induced additional artifacts were seen as signal displacements in the phase-encoding direction. The artifacts were obvious at an iron concentration of 1 mg Fe/ml, barely visible at 0.2 mg Fe/ml, and completely absent at 0.1 mg Fe/ml. Artifacts were also evident with the SPP outside the imaging slice. This further emphasizes the importance of choosing the lowest effective dose when using SPP contrast agents. For the paramagnetic agent, motion propagated artifacts consisted of high and low signal regions in a mosaic pattern