Thomas Beyer

MRI-Based Attenuation Correction for Whole-Body PET/MRI: Quantitative Evaluation of Segmentation- and Atlas-Based Methods

PET/MRI is an emerging dual-modality imaging technology that requires new approaches to PET attenuation correction (AC). We assessed 2 algorithms for whole-body MRI-based AC (MRAC): a basic MR image segmentation algorithm and a method based on atlas registration and pattern recognition (AT&PR). Methods: Eleven patients each underwent a whole-body PET/CT study and a separate multibed whole-body MRI study. The MR image segmentation algorithm uses a combination of image thresholds, Dixon fat–water segmentation, and component analysis to detect the lungs. MR images are segmented into 5 tissue classes (not including bone), and each class is assigned a default linear attenuation value. The AT&PR algorithm uses a database of previously aligned pairs of MRI/CT image volumes. For each patient, these pairs are registered to the patient MRI volume, and machine-learning techniques are used to predict attenuation values on a continuous scale. MRAC methods are compared via the quantitative analysis of AC PET images using volumes of interest in normal organs and on lesions. We assume the PET/CT values after CT-based AC to be the reference standard. Results: In regions of normal physiologic uptake, the average error of the mean standardized uptake value was 14.1% ± 10.2% and 7.7% ± 8.4% for the segmentation and the AT&PR methods, respectively. Lesion-based errors were 7.5% ± 7.9% for the segmentation method and 5.7% ± 4.7% for the AT&PR method. Conclusion: The MRAC method using AT&PR provided better overall PET quantification accuracy than the basic MR image segmentation approach. This better quantification was due to the significantly reduced volume of errors made regarding volumes of interest within or near bones and the slightly reduced volume of errors made regarding areas outside the lungs.

Comparison of Suction Catheter versus Forceps Biopsy for Sampling of Solitary Pulmonary Nodules Guided by Electromagnetic Navigational Bronchoscopy

Background: Electromagnetic navigation has been approved for use as an adjunct to standard bronchoscopy. The diagnostic yield varies depending on the size of the lesion and successful navigation to the lesion. Objectives: The performance of two different biopsy tools, i.e. catheter aspiration and forceps biopsy, in the diagnosis of small pulmonary nodules (SPN) guided by electromagnetic navigational bronchoscopy (ENB) was examined. Methods: 54 patients referred for suspected lung cancer underwent ENB and 55 SPN (<3 cm) were sampled using both techniques. Endobronchial ultrasound (EBUS) was used to verify the accuracy of target lesion localization by ENB. Primary end points of the study were successful navigation to the lesion and a positive diagnosis. Patients were followed until a definitive diagnosis was obtained. Results: All 55 lesions were accessed. Two lesions were excluded from data analysis as the patients were lost to follow-up and their diagnoses could not be confirmed. Of the remaining 53 lesions, 40 samples (75.5%) were diagnostic. Compared to forceps biopsy, catheter aspiration was positively correlated with the success rate (36/40 vs. 22/40; p = 0.035). The diagnostic yield was 93% when EBUS verified the lesion location after navigation and only 48% when lesion location was not confirmed. There were no significant complications. Conclusions: ENB is a useful tool in the evaluation of SPN <3 cm in diameter. For malignant lesions, sampling by catheter aspiration is associated with a higher diagnostic yield than sampling by forceps biopsy alone, in particular when EBUS could not confirm lesion location prior to sampling.

Q value and half-life of double-electron capture in 184Os

The observation of neutrinoless double-beta transitionswould reveal physics beyond the Standard Model, asit would establish neutrinos to be Majorana particles,which implies a violation of the lepton number conserva-tion. Experiments searching for these transitions have fo-cused on the detection of neutrinoless double-beta decay(0x17 ) rather than neutrinoless double-electron capture(0x17x0fx0f). One reason among others is in general the sig-ni cantly shorter half-life of the 0x17 process. However,in the case of neutrinoless double-electron capture, thetransition is expected to be resonantly enhanced if theinitial and the nal state of the transition are degeneratein energy [1{3].In this work, we investigate neutrinoless double-electron capture in

Direct mass measurements of cadmium and palladium isotopes and their double-β transition Q values

The Q-value of the double-electron capture in Cd-108 has been determined to be (272.04 +/- 0.55) keV in a direct measurement with the double-Penning trap mass spectrometer TRIGA-TRAP. Based on this result a resonant enhancement of the decay rate of Cd-108 is excluded. We have confirmed the double-beta transition Q-values of Cd-106 and Pd-110 recently measured with the Penning-trap mass spectrometers SHIPTRAP and ISOLTRAP, respectively. Furthermore, the atomic masses of the involved nuclides Cd-106, Cd-108, Cd-110, Pd-106, Pd-108 and Pd-110 have been directly linked to the atomic mass standard.

TRIGA-SPEC: the prototype of MATS and LaSpec

Investigation of short-lived nuclei is a challenging task that MATS and LaSpec will handle at the low energy branch of Super-FRS at FAIR. The groundwork for those experiments is laid-out already today at the TRIGA-SPEC facility as a powerful development platform located at the research reactor TRIGA Mainz. The latest status, new developments and first results of commissioning runs are presented here.

High‐Precision Mass Measurements At TRIGA‐TRAP

In order to study neutron‐rich nuclides far from the valley of stability as well as long‐lived actinoids the double Penning‐trap mass spectrometer TRIGA‐TRAP has been recently installed at the research reactor TRIGA Mainz. Short‐lived neutron‐rich fission products are produced by thermal neutron‐induced fission of an actinoid target installed close to the reactor core. A helium gas‐jet system with carbon aerosol particles is used to extract the fission products to the experiment. The Penning trap system has already been commissioned. Off‐line mass measurements are routinely performed using a recently developed laser ablation ion source, and the gas‐jet system has been tested. An overview of the experiment and current status will be given.