How fast can we scan patients with modern (digital) PET/CT systems?

PURPOSE

To seek for the minimal duration per bed position with a digital PET system without compromising image quality and lesion detection in patients requiring fast ¹⁸F-FDG PET imaging.

MATERIALS AND METHODS

19 cancer patients experiencing pain or dyspnea and 9 pediatric patients were scanned on a Vereos system. List mode data were reconstructed with decreasing time frame down to 10 s per bed position. Noise was evaluated in the liver, blood pool and muscle, and using target-to-background ratios. Five PET readers recorded image quality, number of clinically relevant foci and of involved anatomical sites in reconstructions ranging from 60 to 10 s per bed position, compared to the standard 90 s reconstruction.

RESULTS

The following reconstructions, which harboured a noise not significantly higher than that of the standard reconstruction, were selected for clinical evaluation: 1iterations/10 subsets/20_sec (1i10 s20_sec), 1i10 s30_sec, and 2i10 sPSF60_sec. Only the 60 s per bed acquisition displayed similar target-to-background ratios compared to the standard reconstruction, but mean ratios were still higher than 2.0 for the 30 s reconstruction. Inter-rater agreement for the number of involved anatomical sites and detected lesion was good or almost perfect (Kappa: 0.64-0.91) for all acquisitions. In particular, kappa for the 30 s per bed acquisition was 0.78 and 0.91 for lesion and anatomical sites number, respectively. Intra-rater agreement was also excellent for the 30 s reconstruction (kappa = 0.72). Median estimated total PET acquisition time for the 1i10 s30_sec, and the standard reconstruction were 4 and 12 min, respectively.

CONCLUSIONS

Fast imaging is feasible with state-of-the-art PET systems. Acquisitions of 30 s per bed position are feasible with the Vereos system, requiring optimization of reconstruction parameters.

Evaluation of a new multipurpose whole-body CzT-based camera: comparison with a dual-head Anger camera and first clinical images

Background

Evaluate the physical performance of the VERITON CzT camera (Spectrum Dynamics, Caesarea, Israel) that benefits from new detection architecture enabling whole-body imaging compared to that of a conventional dual-head Anger camera.

Methods

Different line sources and phantom measurements were performed on each system to evaluate spatial resolution, sensitivity, energy resolution and image quality with acquisition and reconstruction parameters similar to those used in clinical routine. Extrinsic resolution was assessed using ^99mTc capillary sources placed successively in air, in a head and in a body phantom filled with background activity. Spectral acquisitions for various radioelements used in nuclear medicine (^99mTc, ¹²³I, ²⁰¹Tl, ¹¹¹In) were performed to evaluate energy resolution by computing the FWHM of the measured photoelectric peak. Tomographic sensitivity was calculated by recording the total number of counts detected during tomographic acquisition for a set of source geometries representative of different clinical situations. Sensitivity was also evaluated in focus mode for the CzT camera, which consisted of forcing detectors to collect data in a reduced field-of-view. Image quality was assessed with a Jaszczak phantom filled with 350 MBq of ^99mTc and scanned on each system with 30-,20-,10- and 5-min acquisition times.

Results

Extrinsic and tomographic resolution in the brain and body phantoms at the centre of the FOV was estimated at 3.55, 7.72 and 6.66 mm for the CzT system and 2.47, 7.75 and 7.72 mm for the conventional system, respectively. The energy resolution measured at 140 keV was 5.46% versus 9.21% for the Anger camera and was higher in a same manner for all energy peaks tested. Tomographic sensitivity for a point source in air was estimated at 236 counts·s⁻¹·MBq⁻¹ and increased to 1159 counts·s⁻¹·MBq⁻¹ using focus mode, which was 1.6 times and 8 times greater than the sensitivity measured on the scintillation camera (144 counts·s⁻¹·MBq⁻¹). Head and body measurements also showed higher sensitivity for the CzT camera in particular with focus mode. The Jaszczak phantom showed high image contrast uniformity and a high signal-to-noise ratio on the CzT system, even when decreasing acquisition time by 6-fold. Representative clinical cases are shown to illustrate these results.

Conclusion

The CzT camera has a superior sensitivity, higher energy resolution and better image contrast than the conventional SPECT camera, whereas spatial resolution remains similar. Introduction of this new technology may change current practices in nuclear medicine such as decreasing acquisition time and activity injected to patient.

Does PET Reconstruction Method Affect Deauville Score in Lymphoma Patients?

When evaluating ¹⁸F-FDG PET images with the Deauville score (DS), the quantification of tumor and reference organs limits the problem of optical misinterpretation. Compared with conventional reconstruction algorithms, point-spread function (PSF) modeling increases SUVs significantly in tumors but only moderately in the liver, which could affect the DS. We investigated whether the choice of the reconstruction algorithm affects the DS and whether discordance affects the capability of ¹⁸F-FDG PET to stratify lymphoma patients. Methods: Overall, 126 patients with diffuse large B-cell lymphoma were included (56 female and 70 male; median age, 65 y; range, 20-88 y). PET data were reconstructed with the unfiltered PSF method. Additionally, a 6-mm filter was applied to PSF images to meet the requirements of the EANM Research Ltd. (EARL) harmonization program from the European Association of Nuclear Medicine (EANM) (PSF_EARL). One hundred interim PET (i-PET) and 95 end-of-treatment PET (EoT-PET) studies were analyzed. SUV_max in the liver and aorta was determined using automatic volumes of interest and compared with SUV_max in the residual mass with the highest ¹⁸F-FDG uptake. Results: For i-PET, using PSF and PSF_EARL, we classified patients as responders and nonresponders in 60 and 40 cases versus 63 and 37 cases, respectively. Five cases of major discordance (5.0%) occurred (i.e., changes from responder to nonresponder). For Eot-PET, patients were classified using PSF and PSF_EARL as responders and nonresponders in 69 and 26 cases versus 72 and 23 cases, respectively. Three cases of major discordance (3.2%) occurred. Concordance (Cohen unweighted κ) between the PSF and the PSF_EARL DS was 0.82 (95% confidence interval, 0.73-0.91) for i-PET and 0.89 (95% confidence interval, 0.81-0.96) for EoT-PET. The median follow-up periods were 28.4 and 27.4 mo for i-PET and EoT-PET, respectively. Kaplan-Meier analysis showed statistically significant differences in progression-free survival and overall survival among responders and nonresponders no matter which reconstruction was used for i-PET and EoT-PET. Conclusion: Neither DS nor risk stratification of diffuse large B-cell lymphoma patients is affected by the choice of PET reconstruction. Specifically, the use of PSF is not an issue in routine clinical processes or in multicenter trials. These findings have to be confirmed in escalation and deescalation procedures based on early i-PET.

Impact of the EARL harmonization program on automatic delineation of metabolic active tumour volumes (MATVs)

Background

The clinical validation of the EARL harmonization program for standardised uptake value (SUV) metrics is well documented; however, its potential for defining metabolic active tumour volume (MATV) has not yet been investigated. We aimed to compare delineation of MATV on images reconstructed using conventional ordered subset expectation maximisation (OSEM) with those reconstructed using point spread function modelling (PSF-reconstructed images), and either optimised for diagnostic potential (PSF) or filtered to meet the EANM/EARL harmonising standards (PSF₇).

Methods

Images from 18 stage IIIA-IIIB lung cancer patients were reconstructed using all the three methods. MATVs were then delineated using both a 40% isocontour and a gradient-based method. MATVs were compared by means of Bland–Altman analyses, and Dice coefficients and concordance indices based on the unions and intersections between each pair of reconstructions (PSF vs OSEM, PSF₇ vs PSF and PSF₇ vs OSEM).

Results

Using the 40% isocontour method and taking the MATVs delineated on OSEM images as a reference standard, the use of PSF₇ images led to significantly higher Dice coefficients (median value = 0.96 vs 0.77; P < 0.0001) and concordance indices (median value = 0.92 vs 0.64; P < 0.0001) than those obtained using PSF images.

The gradient-based methodology was less sensitive to reconstruction variability than the 40% isocontour method; Dice coefficients and concordance indices were superior to 0.8 for both PSF reconstruction methods. However, the use of PSF₇ images led to narrower interquartile ranges and significantly higher Dice coefficients (median value = 0.96 vs 0.94; P = 0.01) and concordance indices (median value = 0.89 vs 0.85; P = 0.003) than those obtained with PSF images.

Conclusion

This study demonstrates that automatic contouring of lung tumours on EARL-compliant PSF images using the widely adopted automatic isocontour methodology is an accurate means of overcoming reconstruction variability in MATV delineation. Although gradient-based methodology appears to be less sensitive to reconstruction variability, the use of EARL-compliant PSF images significantly improved the Dice coefficients and concordance indices, demonstrating the importance of harmonised-images, even when more advanced contouring algorithms are used.

Electronic supplementary material

The online version of this article (doi:10.1186/s13550-017-0279-y) contains supplementary material, which is available to authorized users.