Implementation of an Automated Respiratory Amplitude Gating Technique for PET/CT: Clinical Evaluation

Abstract

Amplitude gating techniques have recently been shown to be better at suppressing respiratory motion artifacts than phase gating. However, most commercial PET/CT scanners are equipped with phase gating capabilities only. The objective of this article was to propose and evaluate using patient studies an automated respiratory amplitude gating technique that could be implemented on current whole-body PET/CT scanners. A primary design feature of the proposed technique is to automatically match the respiratory amplitude captured during the CT scan with a corresponding amplitude during the PET scan. Methods The proposed amplitude gating technique consists of a CT scan, followed by a list-mode PET scan. The CT scan was acquired while the patient’s respiratory motion was recorded by a monitoring device that determined the respiratory motion amplitude captured during the CT scan. A program was designed to inject triggers into the PET list stream whenever the patient’s respiration crossed a preset amplitude range determined by the captured amplitude during CT. To implement this proposed amplitude gating technique in whole-body PET/CT, a PET-first protocol was necessary to minimize the respiratory baseline drift between the CT and PET scans. In this implementation, a regular PET scan was first acquired over the patient’s whole body but excluding the bed position that covered the lesion of interest. The whole-body CT scan was then acquired, followed by a list-mode PET acquisition over the bed position that covered the area of interest (lesion). The proposed amplitude gating technique was tested using 13 patients with 21 lung or thoracic tumors. Results In the patient studies, the gated images—when compared with the ungated images—showed statistically significant improvements, with an average 27% and 28% increase in maximum and mean standardized uptake value, respectively, for all lesions. Furthermore, the tumors in the gated images showed better contrast using visual inspection and line profiles. Conclusion The implementation of the proposed respiratory amplitude gating technique on current PET/ CT scanners is feasible, and amplitude-matched CT and PET data can be automatically generated using our proposed procedures without requiring patients to hold their breath or increase their radiation exposure.

Application of Partial Volume Effect Correction and 4D PET in the Quantification of FDG Avid Lung Lesions

“…Second, it has been demonstrated that phasebased respiratory gating is less effective than amplitudebased gating, especially in patients with irregular respiratory cycles [13]. Despite this knowledge, phase-based methods of gating remain the most widely investigated in cancer research [15], as in the current study. In addition, six respiratory gates have been suggested as the optimal number in phase-based respiratory gating [38], while we used only four phase gates in order to limit image noise.…”

“…In 2002, Nehmeh et al were the first to perform respiratory gating for PET scanning in clinical setting and found that respiratory gating decreases total lesion volume and increases measured SUV compared to non-gated images [14]. Gating has also been reported to improve the diagnosis of malignant lung lesions and the evaluation of response to radiation treatment [15][16][17][18].…”

Clinical respiratory motion correction software (reconstruct, register and averaged—RRA), for 18F-FDG-PET-CT: phantom validation, practical implications and patient evaluation

“…Several authors have shown that amplitude-based approaches are most robust in the case of irregular breathing patterns compared with phase-based gating approaches. [33][34][35] The Q.Freeze software does not propose any amplitude sampling and only proposes a time sampling.…”

The effect of breathing irregularities on quantitative accuracy of respiratory gated PET/CT

“…All spheres were filled with identical activity concentration of 42.2 kBq/cc (SUV = 15) of 18 F except for the 47 mm sphere which had half of this concentration. The largest sphere had half the concentration in order to reduce the total count rate from the phantom and prevent count rate effects from impacting the image quality.…”

“…The key to a good 4D scan is a highly stable breathing pattern that enables accurate data binning. Amplitude based binning methods 17,18 have been shown to give better results than phase binning in situations when there are breathing period or amplitude variations but is not widely available commercially. Phase binning is particularly prone to respiratory signal baseline drift and amplitude irregularities which lead to binning errors.…”