Improved Characterization of Small SLN Using HD•Chest and FlowMotion in a Rectal Carcinoma Patient

Data courtesy of Royal Brisbane Hospital, Brisbane, Australia

Partha Ghosh, MD, Molecular Imaging Business Unit, Siemens Healthcare |  2014-04-11

History

A 61-year-old male patient with a history of rectal carcinoma treated with recto-sigmoid resection and partial hepatectomy for solitary liver metastases underwent Fludeoxyglucose F18 (18F FDG)* PET/CT for a follow-up.

 

The PET/CT study was performed on Biograph mCT Flow™**. Following non-contrast whole-body CT, the PET acquisition was performed with variable table speed, and the liver and upper abdomen were acquired through integrated respiratory gating, with faster acquisition 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 gated data from the region of the thorax and upper abdomen was reconstructed as HD•Chest with 33% duty cycle in order to obtain relatively motion-free images of the lung for improved evaluation of lung lesions.

 

*Siemens' PETNET Solutions is a manufacturer of fludeoxyglucose F18 injection (18F FDG). Indication and important safety information as approved by the US Food and Drug Administration can be found at the bottom of the page for 18F FDG, adult dose 5-10 mCi, administered by intravenous injection.

Diagnosis

Coronal MIP and thin MIP images of the whole-body PET study shows a solitary focal hypermetabolic nodular lesion in the lung, which is suspicious for malignancy with an SUVmax of 2.9 in the non-gated study. The surgical resection bed in the anterior part of the left lobe of the liver shows normal tracer uptake. Both the renal pelvis and left upper ureter show tracer retention. Mild 18F FDG uptake in bilateral inguinal nodes is likely to be reactive.

 

The HD•Chest reconstruction of the respiratory-gated data of the lung, which is now part of the single scan protocol due to the use of FlowMotion™**, demonstrates sharper delineation of the hypermetabolic lung nodule with higher lesion conspicuity and increased target to background as compared to non-gated acquisition.

 

Quantitative comparison between non-gated reconstruction and HD•Chest shows substantially higher SUVmax,with HD•Chest compared to that obtained from the non-gated reconstruction. SUVmax increased from 2.97 to 3.65 with HD•Chest, an increase of 23% which can be attributed to the lack of peripheral blurring and smaller lesion dimension achieved with HD•Chest by eliminating the respiratory motion artifacts. This SUVmax level is consistent with a diagnosis of malignancy in the pulmonary nodule, possibly secondary to lung metastases from rectal carcinoma.

Comment

This clinical example illustrates the improved visualization and higher quantitative accuracy for small lung nodules that are achieved through amplitude-based, optimized respiratory- gating (HD•Chest), which eliminates respiratory motion-related peripheral blurring and loss of lesion conspicuity. The 23% higher SUVmax obtained with HD•Chest—secondary to elimination of respiratory motion-related partial volume effects and blurring—strongly supports the diagnosis of malignancy in the lung nodule. Although the SUVmax of 2.97 obtained from the nongated study is suggestive of malignancy, the increased SUVmax following elimination of respiratory motion-related effects imparts significant additional diagnostic confidence and also confirms the absence of other lung lesions. CT shows the lung nodule to be 8 mm in diameter. The sharp delineation of such a small nodule with HD•Chest reflects the improved lesion conspicuity, target-to-background ratio and higher quantitative accuracy obtained through the elimination of respiratory motion-related blurring and partial volume effects with HD•Chest.

 

Although respiratory gating helps eliminate respiratory motion and is able to sharply define the lesion in individually 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 uses a portion of the total gated list-mode data with the least motion based on amplitude histogram; this provides relatively motion-free images with higher count statistics for higher image quality and improved small lesion conspicuity. FlowMotion acquisition enables respiratory gating within extremely flexible ranges, which helps generate motionmanaged HD•Chest reconstructions precisely from the regions of interest without undue time penalty.

 

Value of FlowMotion Technology

Accurate SUV quantification is key to management decision-making in lung nodules. SUVmax higher than 2.5 has been shown to have a higher probability of malignancy. Since SUV in lung nodules may be affected by partial volume effects, due to respiratory motion in non-gated PET, motion management in PET acquisition, like HD•Chest, may improve quantification due to elimination of respiratory motion effects. This is particularly important for small nodules with lower levels of hypermetabolism as seen in early lesions. Detection of small nodules with low uptake may also be enhanced by HD•Chest since lesion conspicuity is improved by elimination of respiratory motion-related blurring. Integration of HD•Chest with FlowMotion acquisition offers great flexibility of the area to be covered and opens the possibility of seamless routine use of this technique, with potential improvement in lesion detectability and informed therapy decision. Thus, FlowMotion enables gated acquisition in narrow or wide ranges not limited by bed positions in order to perform acquisition tailored to the patient’s clinical requirements.

Examination Protocol

Scanner:             Biograph mCT Flow

Injected dose:    334 MBq 18F FDG

Scan delay:        1 hour post injection

FlowMotion

Acquisition:        Variable table speed (Figure 1) ultraHD•PET with integrated respiratory gating for thorax and upper abdomen

CT:                       100 kV, 45 eff mAs, 5 mm slice thickness

 

*Fludeoxyglucose F 18 Injection
INDICATIONS AND USAGE
Fludeoxyglucose F 18 injection (18F FDG) is indicated for positron emission tomography (PET) imaging in the following setting:
Oncology: For assessment of abnormal glucose metabolism to assist in the evaluation of malignancy in patients with known or suspected abnormalities found by other testing modalities, or in patients with an existing diagnosis of cancer.

 

 

IMPORTANT SAFETY INFORMATION

Radiation Risks
Radiation-emitting products, including fludeoxyglucose F 18 injection, may increase the risk for cancer, especially in pediatric patients. Use the smallest dose necessary for imaging and ensure safe handling to protect the patient and health care worker.

Blood Glucose Abnormalities
In the oncology and neurology setting, suboptimal imaging may occur in patients with inadequately regulated blood glucose levels. In these patients, consider medical therapy and laboratory testing to assure at least two days of normoglycemia prior to fludeoxyglucose F18 injection administration.

Adverse Reactions
Hypersensitivity reactions with pruritus, edema and rash have been reported; have emergency resuscitation equipment and personnel immediately available.

 

Full prescribing information for Fludeoxyglucose F 18 Injection
Fludeoxyglucose F 18 injection is manufactured by Siemens' PETNET Solutions, 810 Innovation Drive, Knoxville, TN 39732
 

** Biograph mCT Flow and FlowMotion are not commercially available in all countries. Due to regulatory reasons their 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 that were achieved in the customer’s unique setting. Since there is no “typical” hospital and many variables exist (e.g., hospital size, case mix, level of IT adoption) there can be no guarantee that other customers will achieve the same results.