Respiratory gating in PET/CT: A step in the right direction

Journal of Nuclear Cardiology, Mar 2018

Tinsu Pan PhD

A PDF file should load here. If you do not see its contents the file may be temporarily unavailable at the journal website or you do not have a PDF plug-in installed and enabled in your browser.

Alternatively, you can download the file locally and open with any standalone PDF reader:

https://link.springer.com/content/pdf/10.1007%2Fs12350-016-0647-4.pdf

Respiratory gating in PET/CT: A step in the right direction

Received Aug Respiratory gating in PET/CT: A step in the right direction Tinsu Pan 0 0 Reprint requests: Tinsu Pan , Houston, TX , USA - Respiratory motion is inevitable in cardiac imaging with PET as the rest or stress myocardial perfusion imaging (MPI) takes about 6 minutes with 82Rb and 10 to 15 minutes with 13N-ammonia and viability imaging 10 to 30 min with 18F-FDG.1 Figure 1 illustrates an example of respiratory motion between the end-inspiration and end-expiration phases in an 18F-FDG scan. All newer PET scanners are with CT and without transmission line sources.2 CT has shortened the time for the transmission scan for attenuation correction of the PET data from minutes to seconds and could also provide the important information of calcium scores and contrast-enhanced coronary artery CT images to help diagnose heart disease. CT, however, introduces a new problem of potential mis-registration of the CT and PET data due to its fast scan speed resulting in each CT image being a snapshot or a single phase of the heart in respiratory motion. A series of continuous respiratory phases of snapshot CT images may not be suitable for attenuation correction of the PET data. It is important to mitigate the impact of respiratory motion to improve cardiac PET image quality. In the article by Ichikawa et al, the authors proposed an abdominal restriction technique by applying an abdominal belt to restrict respiratory motion in MPIPET. They wrapped a 20-cm abdominal belt around the abdomen of 8 male healthy volunteers (BMI 23±2 and ages 55±17 years) at end-expiration to restrict their respiratory motion. They reported that the motion of the heart in the cranio-caudal direction was significantly reduced from 12.1 ± 6.1 mm without the belt to 8.1 ± 7.1 mm with the belt and that this restriction was well tolerated in the 8 healthy volunteers and subsequent 53 patients (ages 70 ± 10). The authors also reported a small but statistically significant improvement of a qualitative visualization score of 0.42 (0.29 to 0.71) and 0.71 (0.33 to 1.04) in the anterior and inferior walls, respectively, and no change in the lateral walls in a scale of 0 = normal to 4 = defect. Reduction of respiratory motion did not have an impact on the assessment of cardiac functions of ejection fraction or left ventricular end-diastolic or end-systolic volumes. In conclusion, the abdominal belt technique was suggested to be an effective way of reducing the impact of respiratory motion in MPI-PET or even MPI-SPECT imaging. Some limitations were noted. The data were only from rest MPI-PET, not stress MPI-PET; there was no quantitative blood flow measurement; there was no standard for adjusting the abdominal belt other than ‘the belt was tightened as much as possible without causing discomfort to the patient.’ It was not clear if this ‘tolerable’ procedure can be translated into a ‘comfortable’ procedure, which may be the best indicator for success of an MPI-PET scan, and which can be best represented by the regular or normal breathing patterns recorded, but not reported in the study. The belt may need to be loosened between the rest and stress MPI studies to improve patient comfort when the total duration of the rest and stress studies can last over 40 minutes for 13Nammonia and many patients cannot keep still after 20 minutes on the imaging couch. In addition to the proposed abdominal restriction technique, there are other techniques from radiation therapy that are used to mitigate the respiratory motion in treating mobile tumors in the thorax or abdomen. Abdominal compression, similar to the proposed abdominal belt to restrict respiratory motion, can restrict the abdominal motion by applying an abdominal plate against the abdomen under a controlled pressure.3 However, the device is bulky, needs to be setup on a flat-couch, and may not be suitable in an MPI-PET session with EKG leads and wires. Another way of reducing the respiratory motion is to have the patient wear goggles to watch a real-time video of the patient’s respiration level and to ask the patient to exercise respiration in a predefined range. Some may also play a recording of breathing instructions to coach the patient to breath in a shallow manner and in a certain frequency to make respiratory motion regular. Abdominal compression, wearing goggles, and playing breathing recordings have been practiced in radiation therapy. However, it may be impractical to expect all patients to follow any or a combination of these somewhat intrusive procedures. Some may tolerate one procedure better than another, and some may not be able to tolerate any procedure without increasing anxiety to cause unintended increase in motion. A patient could also do perfectly during a training session and do very poorly during the imaging session or vise versa. The best results may come from the patients without any breathing instructions or restrictive devices because most patients breathe shallowly in their (...truncated)


This is a preview of a remote PDF: https://link.springer.com/content/pdf/10.1007%2Fs12350-016-0647-4.pdf

Tinsu Pan PhD. Respiratory gating in PET/CT: A step in the right direction, Journal of Nuclear Cardiology, 2018, pp. 1-3, DOI: 10.1007/s12350-016-0647-4