Improved Visualization of Small Liver Metastases Using HD•Chest and FlowMotion
Data courtesy of Royal Brisbane Hospital, Brisbane, Australia
Author: Partha Ghosh, MD, Molecular Imaging Business Unit, Siemens Healthcare
An 81-year-old male patient with a history of colorectal carcinoma treated with partial colectomy presented with elevated serum carcinoembryonic antigen (CEA). In view of the suspicion of metastases, the patient was referred for a PET•CT scan.
The PET•CT study was performed on a Biograph mCT Flow™* scanner. After the non-contrast, whole-body CT was performed, a whole-body PET acquisition was initiated using variable table speed. The liver and upper abdomen were acquired with integrated respiratory gating. Faster acquisition was used for the extremities, in order to optimize acquisition time.
The whole-body PET study was reconstructed as a non-gated, 200x200 matrix reconstruction. However, the region of the liver and upper abdomen was reconstructed with a higher matrix (400x400) as a non-gated study. The gated data for the same region was also reconstructed as HD•Chest with 50% duty cycle, in order to obtain relatively motionfree images of the liver for improved evaluation of liver metastases. Flow- Motion™ acquisition enabled routine use of HD•Chest as a part of seamless routine acquisition with high flexibility of the range of the region of respiratory gated acquisition.
Coronal maximum intensity projection (MIP) and thin-MIP images of the whole-body PET study show 2 focal hypermetabolic lesions in the liver, which are suggestive of liver metastases. Glucose-avid region in the left lung and another small focal region in right lung are probably related to inflammation. Left renal pelvis shows tracer retention. Note the linear uptake and blurring of the margins CT and fused PET•CT images of the thorax show honeycombing of the left lung and right lung base, which corresponds to high tracer uptake and is suggestive of extensive bilateral inflammatory lesions, probably resolving pneumonitis.
The high-resolution, non-gated reconstruction of the respiratory gated acquisition of the upper abdomen shows the liver metastases as small elongated focal hypermetabolic areas. The elongated nature of the uptake and the blurring of the edges secondary to respiratory motion are especially prominent in the liver lesion near the dome of the diaphragm.
The HD•Chest reconstruction of the respiratory gated data of the liver and upper abdomen demonstrates improved delineation of both the liver metastases with higher lesion conspicuity, increased target to background with improved visibility and sharper definition of the edges, as compared to non-gated acquisition. This is especially conspicuous in the lesion near the dome of the diaphragm.
Quantitative comparison between non-gated reconstruction and HD•Chest shows a substantially higher SUVmax with HD•Chest compared to that obtained from the non-gated reconstruction. SUVmax went from 3.92 to 4.8 with HD•Chest, an increase of 22%, which can be attributed to the lack of peripheral blurring and smaller lesion dimension achieved with HD•Chest by eliminating the respiratory motion effects. FlowMotion technology enables respiratory gated acquisition in flexible ranges as was utilized in this patient who required gating for the liver but not the lung in view of the predominance of liver metastases in colorectal carcinoma.
This clinical example illustrates the significant distortion of small liver lesions with peripheral blurring and loss of conspicuity secondary to respiratory motion when PET is acquired without respiratory gating. This may lead to lower detectability of small liver metastases with PET/CT. Although respiratory gating helps eliminate respiratory motion and is able to sharply define the lesion in individual gated frames, the relatively lower count statistics and higher background noise in the individual frames may hinder visualization of very small lesions or lesions with low uptake. HD•Chest uses amplitude-based gating, which utilizes the portion of the total gated list mode data that has the least motion based on amplitude histogram and provides relatively motion-free images with higher count statistics for improved image quality and small lesion conspicuity.
HD•Chest is an attractive tool for improved delineation of small liver lesions, since it provides relatively motion-free images with sufficient image quality and count density without significant increase in scan time. HD•Chest, when integrated into FlowMotion acquisition, can be used with extreme flexibility, thereby enabling precise definition of the region to be acquired with respiratory gating.
In a recent study** comparing non-gated PET and HD•Chest in 31 patients with liver metastases,1 out of a total of 82 hepatic and 25 perihepatic lesions, 13 new lesions were identified by HD•Chest as compare to standard PET. In this study, 5-minute optimal gating (HD•Chest) acquisition demonstrated improved image quality and 66% higher target to background ratio and 24% higher SUVmax for metastatic lesions as compared to non-gated PET acquired at 2.5 minutes per bed. In a patient with a single lesion seen on standard PET, the use of HD•Chest identified 2 liver metastases, which significantly changed patient management, from surgical removal of solitary metastases to radiofrequency ablation of 2 metastatic lesions. In another patient, HD•Chest helped the physician identify a lesion in the pancreas that had been previously identified as a peritoneal metastases by non-gated PET.
Value of FlowMotion Technology
In view of the therapy options, such as surgical removal of solitary liver metastases, cryotherapy, radiofrequency ablation of individual lesions or chemotherapy in extensive metastases, proper detection of early liver metastases or exclusion of liver lesions assumes a key importance in the therapy decision. Thus, integrated techniques like HD•Chest, which improve the diagnostic confidence and detectability of small liver, lung or upper abdominal lesions without undue time burden, are of value in PET/CT scanning.
Continuous bed motion and anatomybased planning with FlowMotion opens the possibility of seamless, routine use of HD•Chest with the opportunity for improvement in lesion detectability and more informed therapy decisions.
Scanner Biograph mCT Flow
Scan dose 334 MBq 18F FDG
Scan protocol 1 hour post injection delay, FlowMotion acquisition variable table speed.(Figure 1) ultraHD•PET with integrated respiratory gating for upper abdomen.
CT 120 kV, 56 eff mAs, 3 mm slice thickness
* Biograph mCT Flow is not commercially available in all countries. Due to regulatory reasons, its future availability cannot be guaranteed. Please contact your local Siemens organization for further details. ** The statements by Siemens customers described herein are based on results that were achieved in the customer’s unique setting. Since there is no “typical” hospital and many variable exist (e.g., hospital size, case mix, level of IT adoption) there can be no guarantee that other customers will achieve the same results. 1 Van Der Gucht, et al. (2013). European Journal of Radiology, Nov. 2013 online, article in press.