Author: mruiz

The Crystal Clear Collaboration

Scintillating materials are used in high energy and nuclear physics, in astrophysics, in medical imaging, in non destructive testing, in security devices, in geological surveys, and have a number of other industrial uses.

In 1990 the CRYSTAL CLEAR collaboration was set up, and registered as RD-18 by the CERN DRDC committee. The main aim of this project was to develop scintillating materials which would be suitable for use at the LHC collider. Indeed, none of the existing scintillators at that time had the appropriate characteristics for use in the extremely demanding LHC application.

A cut away view of the CMS electromagnetic calorimeter
showing the orientation of the crystals in the end-cap and
barrel sections.

After several years focussing on the development of fast scintillators for a new generation of electromagnetic calorimeters in High Energy Physics (lead tungstate, cesium fluoride, heavy scintillating fluoride glasses), the collaboration decided, in 1997, to turn its attention to the development of scintillating materials and instrumentation for nuclear medicine.

The CRYSTAL CLEAR collaboration has been quite successful. On the basis of our studies, the CMS collaboration decided in 1994 to choose a detector based on the use of PbWO4 scintillator for the electromagnetic calorimeter. But the CRYSTAL CLEAR collaboration at the same time succeeded to create and motivate a community of scientists to develop a new field of applied research on the physics of scintillation processes in solids. This attracted scientists and engineers from other areas making use of scintillating materials, resulting in a total community of about 250 scientists world wide.

We are focussing our attention to the development of a new scintillating materials and a new detector technology for PET, because this is close to the expertise acquired in high energy physics, and because of the growing interest for PET in the medical world. The new technology will be based on the use of new scintillating materials and new photo detectors, which together allow the development of much better detector elements. Regarding the new scintillators, we are concentrating our attention on LuAP:Ce. This material has many very promising properties.

To know more about...

http://cmsdoc.cern.ch/cms/outreach/html/index.shtml CMS outreach pages

http://cern.ch/ttdb TECHNLOGY TRANSFER

http://dmnu-pet5.hcuge.ch/ DIVISION OF NUCLEAR MEDICINE OF GENEVA UNIVERSITY HOSPITAL

AUTHORS: Francisco Martinez & Antonio Guillen (HST 2004 participants)

PET

High school educational material (Teachers version)

POSITRON EMISSION TOMOGRAPHY

EXAMPLE OF CERN TECHNOLOGY SPINOFF

What is PET?

Breast cancer and ganglionar metastasic affection

Positron Emission Tomography, PET, is one form of radio-pharmaceutical diagnosis. PET is used to detect anomalous changes in tissues and organs long before serious symptoms are noticed. A radio-pharmaceutical which emits positrons, the antiparticle of electrons, is administered to the patient. When positrons are emitted, they quickly annihilate with electron in the patient’s body and produce two gamma rays which are detected, pin-pointing where the annihilation took place. PET tells doctors exactly where the radio-pharmaceutical ends up in the body, allowing them to find out whether everything is working as it should.

Principles of PET operation.

Once the pharmaceutical is injected into the patient, the distribution of the tracer can be quantitatively determined within the body (or tumor) from PET image dataset. This image PET is created when the isotropically emitted positron slows down and annihilates with electrons (with an electron close to the nucleus) in tissue producing to back-back 511-keV photons, which are measured in electronic coincidence by using opposing pairs of detector. The two 511-keV annihilation photons have a “mean free path” of about 10.4 cm in water. The human head and chest have dimensions of the order of 20cm This mean that in whole-body PET, approximately only 15% of photons pairs have no interaction within the biological tissue.

European Organization for Nuclear Research

High School Teachers 2004

Radiolabelled tracers. The Medical Ciclotron.

A further advantage of the technique is that the short physical half-life characteristic of so many positron emitting elements ensures low radiation dosage during medical applications. A further important scientific benefit of positron emission nuclides is the availability of the “metabolic” elements 15O, 13N and 11C which facilitate a wide range of studies of biochemical processes in living tissues and organs. The incorporation of these or of the halide 18F by radiochemical syntheses into many natural substances such as carbohydrates, amino acids, or lipid as well as well as into a large number of drugs gives positron emission techniques a remarkable potential for biochemical investigation in man. It has aptly been termed “living autoradiography”.

Radionuclide	Half-life (min)
Oxygen-15	2.07
Nitrogen-13	10.0
Carbon-11	20.4
Fluorine-18	109.8

The band structure of a inorganic scintillator

Inorganic scintillators are usually a single ionic crystal which the valence and conduction bands separated by a 4– to 6eV forbidden energy gap. Ionizing radiation, upon interaction with the crystal, causes electrons to jumps from the valence band to the conducting band. This creates an electron-hole (e-h) pair.
Relaxation of an electron trapped from an excitation level to the ground state results in the emission of a light quantum or scintillation photon.

Examples of Fluorine-18 production
Target material		Nuclear reaction
Ne		20N(d,α)18F
H2O		16O(3He,p)18F
H2O		16O(4He,pn)18F
H2O		18O(p,n)18F

Cyclo layout principle

While 18F has a reasonable half-life (about 110min) and can be shipped, especially via air, for several hundred miles, other PET isotopes have such short half-life that they must be made “on site” to be available in viable quantities to use either clinically. Cyclotrons, combined with robotic “synthesis” units working with the highly radioactive production material coming from the cyclotron, allow production of a wide range of PET labeled molecules.

The Crystal Clear Collaboration at CERN is presently developing several prototype PET scanners involving technologies recently introduced in High Energy Physics. This comprises CLEAR-PET, a small animal PET scanner existing in different versions for rodents, rats and primates, CLEARPEM, a PET dedicated to mammography, a high resolution brain-PET machine, and a high-performance full-body machine with multimodality capability. One key element of these machines is a phoswich detector module based on a combination of LSO (acronym for lutetium orthosilicate) and LuYAP crystal. LuYAP is a mixed lutetium and yttrium aluminum perovskite developed by the Crystal Clear Collaboration with the Bogoroditsk Techno-Chemical Plant in Rusia.

Scintillators for Medical Imaging.

Inorganic scintillator crystal are the most commonly used detectors for PET. Annihilation photons interact within the scintillator though photoelectric and Compton effects. The annihilation photon could deposit a fraction or all of its energy within the crystal. The deposition can occur in one location by photoelectric effect, or at several points within the same crystal by successive Compton interactions.

Why to start with micropets?

Why crystals in medical imaging?

A small cohort of animal subjects with disease is first evaluated with a small animal PET scanner for effectiveness of molecular probes. If the model is reliable, a small number of studies is extended to patients to see if the animal model is relevant in humans (A), using the clinical PET scanner in humans. If the animal model is found to be satisfactory model of human disease, large numbers of animal are studied to provide more information and to refine the model, the imaging probe, the radiolabeled drug, etc (B). Based on these data, larger numbers of patients are then tested (C) in a Phase III trial of the new molecular probe, drug, etc.

The absorbed energy causes the crystal lattice to make a transition to a higher energy state, from which it may undergo decay after a characteristic time by emitting lower energy photons, “the scintillation photons”. This scintillator material is used in conjunction with Photomultiplier Tubes into convert light energy produced from the crystal into an electrical signal. This electric signal provides information of radioisotope tracer uptake.

Detection of photons is a crucial problem for High Energy
Same problem in Medical Diagnostics through imaging

High detection efficiency: keep patient absorbed dose as low as possible
“high density & high atomic number scintillator materials”