Evaluation of noise equivalent count parameters as indicators of adult whole-body FDG-PET image quality.

OBJECTIVES: The aim of this study was to assess variation of qualitative and quantitative PET/CT image quality parameters with acquisition time, injection activity and body mass for a representative group of adults undergoing whole-body PET/CT imaging. METHODS: PET scan data from sixty patients were reconstructed with a scan time of 1, 2 and 3 min/bed position. These images were visually scored and three quantitative parameters were calculated: noise equivalent counts per axial length (NECpatient), noise equivalent count density (NECdensity) and liver signal to noise ratio (liver SNR). The ability of the three quantitative parameters to discriminate qualitative image quality was assessed using ROC analysis. RESULTS: The quantitative parameters were shown to discriminate images of good/excellent quality from those of poorer image quality with a high degree of accuracy (ROC area >0.9); further, NECpatient had significantly higher discrimination than either NECdensity or liver SNR (ROC area = 0.97). CONCLUSIONS: NECpatient, NECdensity and liver SNR all have high discrimination for qualitatively assessed PET image quality. NECpatient in particular is an effective objective indicator of patient image quality, which will help to assess and standardise scan protocols for purposes such as multi-centre research trials.

Monitoring linear accelerator output constancy using the PTW Linacheck.

The PTW-Linacheck was assessed for its ability to monitor linear accelerator radiation output constancy. The key issues that were considered were the setup for daily output measurements, e.g., requirements for build-up and backscatter material, and the reproducibility and linearity of the device with linear accelerator output. An appropriate measurement setup includes a 10 × 10 cm field at 100 cm FSD, 5 cm backscatter, and no added build-up for 4 MeV electron beams, 1 cm added build-up for 6-16 MeV electron beams and 5 cm added build-up for 6-15 MV photon beams. Using this measurement setup, the dose linearity and short-term reproducibility were acceptable; however, the Linacheck should be recalibrated on a monthly basis to ensure acceptable long-term reproducibility.

Monitoring primary breast cancer throughout chemotherapy using FDG-PET.

UNLABELLED: We have compared 2-deoxy-2-[(18)F]-fluoro-D-glucose positron emission tomography (FDG-PET) images of large or locally advanced breast cancers (LABC) acquired during Anthracycline-based chemotherapy. The purpose was to determine whether there is an optimal method for defining tumour volume and an optimal imaging time for predicting pathologic chemotherapy response. METHOD: PET data were acquired before the first and second cycles, at the midpoint and at the endpoint of neoadjuvant chemotherapy. FDG uptake was quantified using the mean and maximum standardized uptake values (SUV) and the coefficient of variation within a region of interest. Receiver-operator characteristic (ROC) analysis was used to determine the discrimination between tumours demonstrating a high pathological response (i.e. those with greater than 90% reduction in viable tumour cells) and low pathological response. RESULTS: Only tumours with an initial tumour to background ratio (TBR) of greater than five showed a difference between response categories. In terms of response discrimination, there was no statistically significant advantage of any of the methods used for image quantification or any of the time points. The best discrimination was measured for mean SUV at the midpoint of therapy, which identified 77% of low responding tumours whilst correctly identifying 100% of high responding tumours and had an ROC area of 0.93. CONCLUSION: FDG-PET is efficacious for predicting the pathologic response of most primary breast tumours throughout the duration of a neoadjuvant chemotherapy regimen. However, this technique is ineffective for tumours with low image contrast on pre-therapy PET scans.