Increased 18F-FDG signal recovery from small physiological structures in digital PET/CT and application to the pituitary gland

Abstract

on conventional pet/ct, and under physiological conditions, the volume of the pituitary gland (pG) is small, and its metabolic activity is commonly comparable to the surrounding background level in 18 f-fDG imaging. We compared the physiological 18 f-fDG uptake of the pG in patients imaged with digital pet (dpet) and with conventional pet (cpet). Additionally, we performed phantom experiments to characterize signal recovery and detectability of small structures. We retrospectively included 10 dPET and 10 cPET patients and measured PG SUVmax, SUVmean and SUVratio (using cerebellum as reference). We imaged a modified NEMA/IEC phantom with both dPET and cPET (background activity 5 kBq/mL, and 3× and 5× higher concentrations in ∅2-20-mm spherical inserts). Mean recovery coefficients (RCmean) and signal-difference-to-noise-ratio (SDNR) were computed to assess lesion detectability. Patients imaged with dPET presented higher PG SUVmax and SUVratio (SUVR) compared to patients imaged with cPET (4.7 ± 2.05 vs. 2.9 ± 0.64, p = 0.004; and 0.62 ± 0.25 vs 0.39 ± 0.09, p = 0.029, respectively), while there was no difference for SUVmean (2.7 ± 1.32 vs 2.1 ± 0.44, p = 0.39). Thus, with a SUV readout scale of 0-5 g/mL, normal PG appeared abnormally hot with dpet, but not with cpet. phantom evidenced higher Rcmean in dpet compared to cpet. for both 3x and 5x measurements, lesion detectability according to size was systematically superior with dPET. in conclusion, patients imaged with dpet presented higher 18 f-fDG physiological uptake of the pG as compared to patients imaged with cPET. These findings were supported by phantom experiments demonstrating superior signal recovery and small region detectability with dpet. Awareness of this new "higher" SUV of the normal 18 f-fDG uptake of the pG is important to avoid potential pitfalls in image interpretation, notably in oncologic patients treated with immunotherapy, who are at increased risk to develop hypophysitis.

SARS-CoV-2 causes brain inflammation and induces Lewy body formation in macaques

“…In humans and macaques, the volume of the pituitary gland is small, and under physiological conditions, its metabolic activity is comparable to the background level of the entire brain (16, 17) . The 18 F-FDG uptake of the pituitary gland may even be underestimated due to the partial-volume-effects that affect the emission signal recovery (16) .…”

“…In humans and macaques, the volume of the pituitary gland is small, and under physiological conditions its metabolic activity is comparable to the background level of the entire brain (16,17).…”

“…The 18 F-FDG uptake of the pituitary gland may even be underestimated due to the partial-volumeeffects that affect the emission signal recovery (16). Because pituitary gland tissue expresses angiotensin-converting enzyme 2 (ACE2) (18), the increased 18 F-FDG uptake may be a direct effect of the infection or an indirect effect due to either a (reversible) hypophysitis, or transient hypothalamic-pituitary dysfunction.…”

Digital PET/CT allows for shorter acquisition protocols or reduced radiopharmaceutical dose in [18F]-FDG PET/CT

“…2 ). Previous studies report increased signal recovery from small structures in digital PET/CT systems [ 26 ], and further studies are needed to investigate the impact of shorter examinations or low dose protocols on small or low-uptake lesions. Reader bias was reduced using reviewers who had not seen the cases prior to the study.…”

Comparing lesion detection efficacy and image quality across different PET system generations to optimize the iodine-124 PET protocol for recurrent thyroid cancer

“…The recently introduced "digital" silicon photomultiplier-based (SiPM-based) PET/CT systems show a higher coincidence time resolution and a higher spatial resolution [10] (compared to conventioanl PET/CT systems). These properties were associated with a higher image quality and a higher detectability of small lesions in phantom settings and clinical applications in different studies using 2-deoxy-2-[fluorine-18]-fluoro-D-glucose ( 18 F-FDG) [11][12][13][14] and, most recently, using [gallium-68]gallium-prostate-specific membrane antigen-11 [15].…”