Comparison of a Free-Breathing CT and an Expiratory Breath-Hold CT with Regard to Spatial Alignment of Amplitude-Based Respiratory-Gated PET and CT Images

Abstract

Respiratory motion during PET has a significant effect on the quantification of radiotracer uptake in PET images. Even when respiratory motion is considered using PET gating techniques, inaccuracies in standardized uptake values can be caused by inappropriate attenuation correction due to a spatial mismatch between PET and CT. In this study, the effect of breath-hold CT imaging on the spatial match between CT and amplitude-based respiratory-gated PET images is investigated. Methods: Wholebody 18 F-FDG PET/CT imaging was performed in 52 patients with 125 lung lesions. 18 F-FDG PET was performed using optimized, amplitude-based respiratory gating. For CT, 36 patients were randomly assigned to the free-breathing (FB) group and 16 to the restexpiratory breath-hold (BH) group. Spatial mismatch between the PET and CT images was quantified by measuring the distance between the centroids of PET and CT lesions and calculating the Jaccard similarity coefficient (JSC). Results: In the upper lobes, the average distance between the centroids of the PET and CT lesions was 4.7 ± 3.1 and 6.0 ± 3.0 mm for the FB and BH groups, respectively (P 5 0.11). For the middle and lower lobes, the distances were 5.8 ± 4.3 and 5.1 ± 2.9 mm (P 5 0.70), respectively, and for the central region 4.8 ± 4.6 and 5.6 ± 2.0 mm (P 5 0.24), respectively. The JSC for the upper lobes was 0.28 ± 0.17 and 0.28 ± 0.19, for the FB and the BH group, respectively (P 5 0.83). For the middle and lower lobes, the JSC was 0.22 ± 0.16 and 0.28 ± 0.18 (P 5 0.20), respectively, and for the central region 0.39 ± 0.17 and 0.13 ± 0.04 (P 5 0.04), respectively. Conclusion: Providing breathing instructions to the patients during the CT acquisition did not improve the spatial alignment between the respiratory-gated PET images and the CT images. The difficulty experienced in using this clinical protocol, such as patient compliance and operator dependence, emphasizes the need for other strategies.Key Words: amplitude-based optimal respiratory gating; lung tumors; standardized uptake value; breath hold CT; spatial alignment PET combined with CT is an essential multimodality molecular imaging method for accurate staging and diagnosis of a variety of diseases, particularly in oncology (1,2). The advantage of combined PET/CT imaging is that it provides both anatomic and molecular information on the patient, improving detection, localization, and characterization of disease (2). Furthermore, the CT scan can be used for PET attenuation correction. Quantitative indices in PET, such as the standardized uptake value (SUV) (3), metabolic volume, and total lesion glycolysis (4,5), can be used to diagnose the disease, to provide prognostic and predictive information, and to optimize radiotherapy planning. Furthermore, it has been established that molecular imaging with PET is valuable in the early assessment of therapy response of several tumor types (6-9).During PET acquisition, patients are instructed to breathe freely because of the relatively long image acquisition times. As a cons...

Evaluating two respiratory correction methods for abdominal PET/MRI imaging

“…The image blur induced by respiratory motion was reduced and the SUV max and SUV mean for the lesions increased significantly. However, the results of end-expiratory respiratory gating were inconsistent with those of many previous reports [ 8 , 9 , 23 ]. According to the model of end-expiratory respiratory gating as shown in Fig.…”

“…For example, end-expiration respiratory gating is based on the observation that the patients usually have a quiescent period after end-expiration during the breathing cycle. Only the counts acquired during the quiescent period were considered valid and used for reconstruction [ 8 , 9 ]. However, these respiratory motion correction methods are seldom used in routine clinical scanning.…”

Evaluating Two Respiratory Correction Methods for Abdominal PET/MRI Imaging

“…The image blur induced by respiratory motion was reduced and the SUV max and SUV mean for the lesions increased signi cantly. However, the results of end-expiratory respiratory gating were inconsistent with those of many previous reports [8,9,22].…”

“…For example, end-expiration respiratory gating is based on the observation that the patients usually have a quiescent period after end-expiration during the breathing cycle. Only the counts acquired during the quiescent period were considered valid and used for reconstruction [8,9]. However, these respiratory motion correction methods are seldom used in routine clinical scanning.…”

The impact of respiratory gated positron emission tomography on clinical staging and management of patients with lung cancer

“…This is an important issue that needs to be addressed, since spatial mismatching between PET and CT images can result in inappropriate attenuation correction, which may in turn result in misdiagnosis. Optimizing the spatial matching of PET and attenuation CT images in combination with the ORG algorithm is the subject of ongoing study at our institute [19]. Unfortunately, due to the limited detailed follow-up data and number of patients in which N-stage migration occurred, no definitive conclusion can be drawn on whether respiratory gating has a clinically significant impact on the false-positive or negative rates for hilar and mediastinal lymph node staging, though this will be subject of ongoing study.…”