Abstract
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Introduction: New digital cameras are currently available worldwide. Different vendors are promoting technical specifications for the use in reducing patient radiation exposure from injected radiopharmaceutical and/or reduced patient imaging time under the camera. A very commonly used study is NaF PET/CT for metastatic workup which might replace the SPECT agent Tc99m MDP. The availability, cost and radiation burden are points of debate for the wider application of this imaging modality that have high resolution and high sensitivity. At our center, we are utilizing this modality as routine for imaging bone metastasis and other bone pathologies commonly imaged with the conventional methods. We propose a study to evaluate the feasibility of acquiring patients with 80% reduction of patient acquisition time.
Methods: All studied population who are referred for NaF PET/CT to assess the presence of osteoblastic bone metastasis were injected with 0.06 mCi/Kg as per our center imaging protocol with an average injected dose of 5.46 mCi (4.42 mCi- 7.04 mCi). After an uptake period of averaged 70.92 min (48 - 86 min), images of the whole body from vertex to toes were acquired on General Electric MI PET/CT system with low dose CT initially for attenuation correction and anatomical localization. Immediately a fast PET acquisition was done using the following parameters (Table 1). This was followed by a repeat PET acquisition only using our routine imaging parameters (Table 1). The second PET acquisition did not require a repeat CT, as patient was instructed to remain still during the imaging period to avoid mis-registration and the need to repeat CT for a second time; thus increasing the radiation exposure delivered to patient from CT component. Images were interpreted by two independence experienced nuclear medicine physicians. Image quality of both acquisition methods were evaluated in terms of contrast, resolution, number of lesions.
Results: Fast acquisition PET was done for the whole body in not more than 3.5 minute. Following this scan, normal routine scan required not more than 16 min. This translate into reduction of acquisition time by 80% using the fast PET protocol. Images were reconstructed as per proposed parameters and image quality appeared consistently similar in quality by two readers. We were able to perform this protocol in total 14 patient (7 patient from BMI group less than 33) as in figure 1. The other patient group were from the BMI group between (33.1-40) as in figure 2. The group above 40.1 BMI were not represented in this study. Images of fast PET was slightly noisy compared to the routine PET; however, all lesions were identified and no single lesion was missed on the fast acquisitions. Both acquisition methods allowed high resolution for lesions noted.
Conclusions: Using fast PET acquisition for NaF PET/CT study in digital system is possible. The feasibility of this approach allows the possibility to scan patients faster thus increasing the number of patient scanned per day. Claustrophic patients who are reluctant to complete the lengthily procedure might benefit from such approach. The possibility of utilizing this technique for fast screening scan and following it with a dedicated longer acquisition for certain body part is also an option that require further evaluation. The limitation of this study was in the absence of group above 40.1 BMI. Lesion by lesion statistical analysis was not included in this part of work.
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