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EH 1_2015

Hamamatsu offers a comprehensive range of MPPCs for PET and TOF-PET imaging.Arrays and modules are available both as standard or customised solutions, utilising Through Silicon Via (TSV) technology.TSV connections eliminate the need for wire bonding, allowing for a very compact package with minimal dead space. P H O T O N I S O U R B U S I N E S S www.hamamatsu.com Multi-pixel Photon Counters (MPPCs) for Positron Emission Tomography (PET) Features: n Extremely low afterpulse and crosstalk n 3.2 mm pitch (3 x 3 mm active area) n High gain and high speed n Insensitivity to magnetic fields n Modules available with integrated ASICs n Chip on board (COB) packaging EUROPEAN HOSPITAL  Vol 24 Issue 1/15 6 EH @ ECR From 2009-2014 Harald Quick was professor of MR imaging at the Institute for Medical Physics, University of Erlangen, where he was also Deputy Director of the Institute. In February 2014 he was appointed Professor for High Field and Hybrid MR Imaging as well as Director of the Erwin L Hahn Institute for MR Imaging, University of Duisburg- Essen. As well as conducting research at Duisburg-Essen Prof. Quick has been a research associate in the Department for Radiology at Zurich’s University Hospital and at Johns Hopkins University in Baltimore, USA. Calculating a patient’s attenuation correction MRI-based AC may work better than CT-AC Whole body PET/MR image of a patient with metastases in the pelvic area: (A) PET without attenuation correction; (B) MRI-based attenuation correction; (C) PET after attenuation correction; (D) T-1-weighted MRI and (E) fused whole-body PET/MRI with fusion of (C) and (D) Report: Sascha Keutel PET/MRI scanners have great poten- tial because they combine the strengths of two different systems. Previous problems resulting from respective, mutually exclusive physi- cal effects of both procedures have been resolved. Now these scanners are being introduced to the hospital and assist in the detection of the position and spread of tumours as well as their metabolic activity, says Dr Harald H Quick, Professor for High-Field and Hybrid MRI Imaging at Duisburg-Essen University. PET has high sensitivity. The sys- tem can locate and measure the very smallest amounts of radiotracers in tumours and metastases and it also makes it possible to quantify their activity. ‘This is important because it allows us to classify and dif- ferentiate different tumours based on certain thresholds,’ Professor Quick explains. ‘PET also allows us to monitor a therapy after the initial diagnosis and start of treat- ment and shows how the activity of cell lesions develops over time and whether or not the treatment is hav- ing the desired effect.’ To fully utilise PET strengths, attenuation correction (AC) is need- ed. This correction is carried out by software that, in turn, is based on a mathematical solution automatically implemented by the scanner. To make this work, you need to know exactly where in a patient’s body photons attenuate in the tissue on their way to the PET detector, and then it becomes possible to calcu- late the AC and thus determine the correct tracer activity in the tumour. To date, AC is still required for all PET/CT hybrid systems – however, with the advantage that the raw data of CT imaging can be directly uti- lised for the AC of the patient tissue. However, with PET/MRI, AC must be performed with new MRI-based procedures. At the centre of this development are the Dixon method sequences, currently experiencing a revival in the context of MRI-based attenuation correction procedures. The procedure involves the attri- bution of different levels of attenua- tion to different types of tissue (air, fat, soft tissue, bone). ‘We know topographically – similar to maps – which types of attenuating tissues are in which place. ‘This can then be utilised in 3-D to work out the patient’s attenuation correction,’ he explains. Although this works well, and is already integrated into clinical routine, room remains for improve- ment. With the help of comparative examinations, Prof. Quick and team are trying to determine how well MRI-based AC works compared to CT-AC. ‘Bones attenuate the PET signal comparatively strongly. The attenuating components of bones are not very visible in the MRI image and therefore cannot be ade- quately corrected,’ he explains. This could change with the help of ultra-short TE pulse sequences (UTE), i.e. ultra-short echo time sequences. These facilitate the detection of cranial bones in the head and therefore improve the information on brain activity quan- tification. ‘We have thus created the opportunity to add another dimen- sion to the above mentioned maps,’ Prof. Quick explains, significantly adding: ‘If, in the future, we want to look at the Alzheimer tracer distribution in the brain, it will be important to account for the bones as such (and not soft tissue as is currently the case) so that we can determine activity more precisely.’ Technical pitfalls Further technical obstacles that PET/MRI scanner manufacturers must overcome are the materials used. As is common in MRI imag- ing, RF receiver coils are used. These coils are within the field of the PET detector while the PET and MRI data are being acquired, and they attenuate the PET signals accordingly. Therefore, manufactur- ers should design the RF receiver coils in a way that makes them as PET-transparent as possible. This applies to the materials used, plus distribution and the design. Manufacturers and researchers hope to integrate the motion correc- tion in its entirety into the examina- tion procedure. The PET/MRI data are currently acquired independent- ly and simultaneously, but more or less side by side. The objective is to utilise the tech- nical opportunities of MRI imaging, to detect the patient’s head, respira- tory and heart movements and to correct the PET data helped by this information on movements – mean- ing to achieve a more precise image of the moving organs, tumours or smaller lesions. HD-PET is another feature that will enhance the world of PET/ MRI. High Density is set to improve the spatial resolution of PET, which tends to reduce towards the edge of the image field for technical rea- sons. This effect can be corrected with the help of a mathematical model (point spread function, PSF), which can restore the resolution within this border area. ‘This,’ Prof. Quick explains, ‘helps to visualise the laterally situated, smaller lesions in the body better.’ Continued f Future ESC Presiden ‘A new world is emerging with IT; we’ve only seen the tip of the ice- berg.’ How is the ESR tackling the chal- lenge of training harmonisation? ‘The ESR Training Curriculum pro- motes a five-year training plan. Up to now, 66 countries have endorsed it. ECR 2015 will be organised around the curriculum to stress its importance. However, we can only incite people to follow our recom- mendations – training remains a national decision.’ The new Spanish training scheme is at odds with these recommenda- tions and raises concerns among radiologists… ‘This scheme plans to fuse radiology and nuclear medicine during the first two years of training, leaving only two years of actual specialisa- tion after that. ‘In principle, I’m not against the idea of joining nuclear medicine and radiology; some countries do that; but we only have four years of spe- cialisation and wish we had more time for clinical training.’ How short will training be now? ‘Many things must be discussed before the scheme is implemented. For instance, not every department in Spain offers both radiology and nuclear medicine training.

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