The Ionising Radiation (Medical Exposure) Regulations require employers to appoint suitable medical physics experts (MPE) for Nuclear Medicine services, and they also define the areas where MPEs are required to provide advice and specify matters that they must contribute towards. Applications for employer licences under IR(ME)R require employers to specify the level of MPE support available and if this is provided by on-site MPEs or remotely. Assessment of these applications by the Administration of Radioactive Substances Advisory Committee (ARSAC) has highlighted variability in the levels of MPE support being provided for similar services across the UK. A working party including representatives from IPEM, ARSAC, BIR and BNMS was formed and has produced these recommendations on MPE support. Nuclear medicine services were divided into seven broad categories and MPE support for each category has been considered. However, some services that differ from the scenarios provided in this guidance may require different levels of MPE support. PET/CT and γ camera imaging have been considered separately here, although it is recognised that both PET/CT and γ cameras are often sited within the same department in many centres. The separation has been done for pragmatic purposes, as there are felt to be sufficient differences in the MPE role requirements. This guidance sets out recommendations for MPE support, and broader physics support, to run a safe nuclear medicine service and defines the responsibilities of these staff for a range of clinical nuclear medicine services. The recommendations on MPE support made are advice, but will assist employers in meeting regulatory requirements.

The PLS agreement was sensitive to the Y lung background correction ROI, potentially explaining a previously published controversy. The mean activity and absorbed dose agreement for the metastatic lesions was poorer than the healthy liver volumes studied here.

TO THE EDITOR:We were interested in the conclusions of Schepis et al. (1), who stated that there is good agreement between left ventricular (LV) ejection fraction (LVEF) and LV functional parameters estimated using CT and gated SPECT across a wide range of clinically relevant values. They appear to base this statement on the good correlation between parameters estimated using the 2 techniques. However, good correlation does not, in itself, indicate good clinical agreement (2).The authors presented Bland-Altman plots and reported limits of agreement. These are a good indicator of the level of clinical agreement, but the results shown were not adequately discussed. We would argue that limits of agreement of 615.1% on LVEF, where the threshold of normality is 50% and mean values in the study were 59% (SPECT) and 60% (CT), do not indicate good agreement, because the potential level of difference in individual cases is large. Similarly, the limits of agreement for end-diastolic volume and end-systolic volume of 651.7 mL and 632 mL, respectively, do not indicate good agreement.The authors' conclusions are somewhat inconsistent. They suggest that although the techniques agree for LVEF, they should not be used interchangeably for LV volumes; LVEF is calculated from LV volumes.Intraobserver reproducibility was reported as excellent for SPECT. The SD of 4.6% is again high relative to the normal threshold; a potential error of greater than 4.6% in 1 in 3 patients is significant. Interobserver error was not reported for SPECT but is likely to be higher than intraobserver error. The 6.4% SD of interobserver differences for CT is high. The authors should investigate the sources of these differences; in our experience, intra-and interobserver differences of this magnitude are unusual.A further point of interest is the systematic difference between the 2 techniques in the estimation of muscle mass. In determining likely explanations, it would be useful to know the extent of myocardium included and whether analysis of the SPECT images included nonperfused muscle.We would also like to point out an error in the presentation of data. The percentage mean differences shown in Table 2 are given in the text as SD on the absolute mean difference; the actual SDs are considerably larger. This may lead to an incorrect conclusion regarding intraobserver reproducibility.In conclusion, we believe that the data show poor intraobserver reproducibility in the estimation of LVEF and very poor clinical agreement between SPECT and CT for the estimation of LVEF and LV functional parameters. LVEF and LV functional parameters as determined by 64-slice CT do not agree with gated SPECT and should not be used interchangeably. Furthermore, the large random differences between the techniques suggest that neither provides a clinically reliable measure of LVEF in this study. agreement in our study. The latter, however, provide no objective cutoff value above which intermethod agreement is considered significant or insufficient. Therefore, it must remain a m...