PEM

	PEM
Home Research YAP-(S)PET YAP-(S)PET+ CT PEM SPEM SiPM DoPET Reconstruction Simulation MRI 7 Tesla - MRI People Publications Job Opportunities Contact Links	Positron Emission Mammography Positron Emission Tomography is a functional imaging technique which is able to distinguish between normal and cancerous tissue on the basis of physiological properties of cells. The utility of PET technique in breast cancer has been clinically assessed for the staging of tumours and the follow up of the therapy. But the characterization of primitive breast lesions, in order to make early diagnosis, is limited by the poor spatial resolution of whole body PET scanners. Thus, small size breast lesions (<5-7mm) can't be localized. PEM (Positron Emission Mammography) is an advanced technique which exploits PET principle, trying to overcome the limitations of whole body PET scanners. A PEM scanner is usually made of two planar detectors which compress the breast in the same projection used by X-ray mammography. This configuration has many advantages i.e.: higher sensitivity, better spatial resolution, less noise due to movement, possibility of multi-modality imaging (co-registration RX-PET). YAP-PEM prototype A dedicated PEM prototype is being developed by FIIG, called YAP-PEM. It is a double head, parallel planes device which is expected to detect tumours of 5 mm diameter when the ¹⁸F-FDG tumour/background specific activity ratio is 10:1, according to Monte Carlo simulations. Each detector head is made of a pixellated scintillator coupled to an array of position sensitive PMTs (shown in Fig.1). The scintillator is composed of 30x30 YAP:Ce(Al) pixel elements with 2x2 mm² pitch and 30 mm depth; thus, the overall detection area is 6x6cm². The 9 PS-PMTs used to detect light from scintillator have a very high packing fraction, in fact their active areas cover 78% of the whole. A dead zone is created by those 22% of crystal pixels facing the area between neighbouring photocatodes. To recover light coming from this zone, a light diffuser can be used. Each PMT has 6X+6Y position signals, so 54X+54Y outputs should be amplified and acquired to perform the read out of an array of 9 PMTs. In order simplify electronics, resistive network method is implemented. As a first choice the PMTs are readout by 9 independent linear resistive chains, thus reducing the signals to 2X+2Y each (18X+18Y in total). Fig.2 shows the very good pixel identification performances (simple Anger logic is used) of the device in this configuration, both with and without light guide. A new readout method is now being investigated using a big resistive network, common to all PMTs. In such a way only 2X+2Y position signals are needed in principle; but, as a matter of fact, noise prevent us from distinguish small signals. To overcome this problem, 4 extra outputs have been added and a new iterative method was implemented to perform pixel reconstruction. This method seems to be promising, even if much work must be done to make the system less noisy. In the meanwhile, a new electronic board has been developed which performs the analogue OR of the 9 last dynode signals to give a single trigger. All the electronic boards needed in this configuration (HV dividers, resistive chain, amplifications, trigger), are being optimized by now. Also, they are shaped to fit in the aluminium housing we have designed for each detector head (Fig.3). The side of the case proximal to the patient is made of tungsten, one HVL thick at 511 keV, so as to reduce radiation background from the heart. Figure1: YAP-PEM design and components. Figure2: Flood field irradiations @ 511 keV of a single YAP-PEM head with (right) and without (left) light guide. Figure3: YAP-PEM single head. Literature Belcari, N, Camarda, M, Del Guerra, A, Herbert, DJ, et al., "Novel high resolution detectors for Positron Emission Tomography (PET)", Nucl Phys B (Proc Suppl) 2003 :125 ; 48-52. Herbert, DJ, Belcari, N, Camarda, M, Del Guerra, A, et al., "Development of a planar head PEM system based on an array of PSPMT and YAP crystals", Conference records of the 2003 IEEE-NSS-MIC. Portland, Oregon (USA), October 19-26, 2003. ISBN 0-7803-8258-7 (CD–Rom), M6-119 (2003). Belcari, N, Camarda, M, Del Guerra, A, Herbert, DJ, et al., "Detector development for a novel Positron Emission Mammography scanner based on YAP:Ce crystals mammography", Nucl Instr and Meth 2004:525 A; 258-262. Motta, A, Righi, S, Del Guerra, A, Belcari, N, et al., "A full Monte Carlo simulation of the YAP-PEM prototype for breast tumor detection", Nucl Instr and Meth 2004: 527 A; 201-205. Camarda, M, Belcari, N, Del Guerra A, et al., "Development of a PEM camera for breast cancer imaging", Biomedizinische techik (supp.1 part 2) 2005:50; 1209-1210.
Last updated 02/03/2009

Positron Emission Mammography

Positron Emission Tomography is a functional imaging technique which is able to distinguish between normal and cancerous tissue on the basis of physiological properties of cells. The utility of PET technique in breast cancer has been clinically assessed for the staging of tumours and the follow up of the therapy. But the characterization of primitive breast lesions, in order to make early diagnosis, is limited by the poor spatial resolution of whole body PET scanners. Thus, small size breast lesions (<5-7mm) can't be localized.
PEM (Positron Emission Mammography) is an advanced technique which exploits PET principle, trying to overcome the limitations of whole body PET scanners. A PEM scanner is usually made of two planar detectors which compress the breast in the same projection used by X-ray mammography. This configuration has many advantages i.e.: higher sensitivity, better spatial resolution, less noise due to movement, possibility of multi-modality imaging (co-registration RX-PET).

YAP-PEM prototype

A dedicated PEM prototype is being developed by FIIG, called YAP-PEM. It is a double head, parallel planes device which is expected to detect tumours of 5 mm diameter when the ¹⁸F-FDG tumour/background specific activity ratio is 10:1, according to Monte Carlo simulations. Each detector head is made of a pixellated scintillator coupled to an array of position sensitive PMTs (shown in Fig.1). The scintillator is composed of 30x30 YAP:Ce(Al) pixel elements with 2x2 mm² pitch and 30 mm depth; thus, the overall detection area is 6x6cm². The 9 PS-PMTs used to detect light from scintillator have a very high packing fraction, in fact their active areas cover 78% of the whole. A dead zone is created by those 22% of crystal pixels facing the area between neighbouring photocatodes. To recover light coming from this zone, a light diffuser can be used. Each PMT has 6X+6Y position signals, so 54X+54Y outputs should be amplified and acquired to perform the read out of an array of 9 PMTs. In order simplify electronics, resistive network method is implemented. As a first choice the PMTs are readout by 9 independent linear resistive chains, thus reducing the signals to 2X+2Y each (18X+18Y in total). Fig.2 shows the very good pixel identification performances (simple Anger logic is used) of the device in this configuration, both with and without light guide.
A new readout method is now being investigated using a big resistive network, common to all PMTs. In such a way only 2X+2Y position signals are needed in principle; but, as a matter of fact, noise prevent us from distinguish small signals. To overcome this problem, 4 extra outputs have been added and a new iterative method was implemented to perform pixel reconstruction. This method seems to be promising, even if much work must be done to make the system less noisy. In the meanwhile, a new electronic board has been developed which performs the analogue OR of the 9 last dynode signals to give a single trigger. All the electronic boards needed in this configuration (HV dividers, resistive chain, amplifications, trigger), are being optimized by now. Also, they are shaped to fit in the aluminium housing we have designed for each detector head (Fig.3). The side of the case proximal to the patient is made of tungsten, one HVL thick at 511 keV, so as to reduce radiation background from the heart.

Figure1: YAP-PEM design and components.

Figure2: Flood field irradiations @ 511 keV of a single YAP-PEM head with (right) and without (left) light guide.

Figure3: YAP-PEM single head.

Literature

Belcari, N, Camarda, M, Del Guerra, A, Herbert, DJ, et al., "Novel high resolution detectors for Positron Emission Tomography (PET)", Nucl Phys B (Proc Suppl) 2003 :125 ; 48-52.

Herbert, DJ, Belcari, N, Camarda, M, Del Guerra, A, et al., "Development of a planar head PEM system based on an array of PSPMT and YAP crystals", Conference records of the 2003 IEEE-NSS-MIC. Portland, Oregon (USA), October 19-26, 2003. ISBN 0-7803-8258-7 (CD–Rom), M6-119 (2003).

Belcari, N, Camarda, M, Del Guerra, A, Herbert, DJ, et al., "Detector development for a novel Positron Emission Mammography scanner based on YAP:Ce crystals mammography", Nucl Instr and Meth 2004:525 A; 258-262.

Motta, A, Righi, S, Del Guerra, A, Belcari, N, et al., "A full Monte Carlo simulation of the YAP-PEM prototype for breast tumor detection", Nucl Instr and Meth 2004: 527 A; 201-205.

Camarda, M, Belcari, N, Del Guerra A, et al., "Development of a PEM camera for breast cancer imaging", Biomedizinische techik (supp.1 part 2) 2005:50; 1209-1210.