Name: a basic positron emission tomography system constructed to locate a radioactive source in a bi-dimensional space
Uploaded: 2016-02-01T13:00:00
Description: Watch this Scientific Journal Video about A Basic Positron Emission Tomography System Constructed to Locate a Radioactive Source in a Bi-dimensional Space at JoVE.com

We are very grateful for the financial support of the Physics Department of CINVESTAV. We also want to thank our technician Marcos Fontaine Sanchez for his remarkable assistance with the set up. Thanks a lot to Sarah LaPointe for reviewing the English-language of this document.

1. Preparation of the PET Setup
<ol>
	<li>Prepare the PMT&#39;s coupled with plastic scintillator pieces. Depending on the kind of PMT (size, shape of the photocathode) build an adequate scintillator piece to fit with the photocathode of the PMT.
	<ol>
		<li>Wrap the scintillator pieces with black tape. Leave one side uncovered, as it will be coupled with the PMT light entrance. 
		NOTE: It is important that these pieces are previously polished to avoid light accumulation losses.</li>
	</ol>
	</li...

<ol>
	<li>Cerello, P., Pennazio, F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+innovative+detector+concept+for+hybrid+4D-PET/MRI.">An innovative detector concept for hybrid 4D-PET/MRI.</a> Imaging. Nucl. Instr. Meth. Phys. Res. 702, 1-3 (2013).</li><li>Muehllerher, G., Karp, J. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Positron+tomography+emission.">Positron tomography emission.</a> Phys. Med. Biol. 51, R117-R137 (2006).</li><li>Conti, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=State+of+the+art+and+challenges+of+time+of+flight+PET.">State of the art and challenges of time of flight PET.</a> Physica Medica. 25 (1), 1-11 (2008).</li><li>Abreu, Y., Pi&#241;era, I., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Simulation+of+a+PET+system+and+study+of+some+geometry+parameters.">Simulation of a PET system and study of some geometry parameters.</a> AIP conference. 1032, 219-221 (2008).</li><li>Langner, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Development of a parallel Computing optimized head movement correction method in PET. , (2003).</li><li>Budinger, T. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Time-of-flight+PET.">Time-of-flight PET.</a> J. Nucl Med. 28 (3), 73-78 (1983).</li><li>Leo, W. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Techniques for Nuclear and Particle Physics Experiments. , (1987).</li><li>Budinger, T. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Instrumentation+trends+in+nuclear+medicine.">Instrumentation trends in nuclear medicine.</a> Semin Nucl Med. 7 (4), 285-297 (1977).</li><li>Burnham, C., Bradshaw, J., Kaufmann, D., Chesler, D., Browner, G. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Positron+tomography+employing+a+one+dimension+BGO+scintillation+camera.">A Positron tomography employing a one dimension BGO scintillation camera.</a> IEEE Trans. Nucl. Sci. 30 (1), 661-664 (1983).</li><li>Burnham, C., Bradshaw, J., Kaufmann, D., Chesler, D., Steams, C. W., Browner, G. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Design+of+a+cylindrical+shape+scintillation+camera+for+positron+tomographs.">Design of a cylindrical shape scintillation camera for positron tomographs.</a> IEEE Trans. Nucl. Sci. 32 (1), 889-893 (1985).</li></ol>

One important aspect of this system is to have a very good control over spatial and time resolutions. The spatial resolution of PET is limited by the physical characteristics of the radioactive decay and the annihilation, but also by technical aspects of the coincidence registration (steps 1.1 and 1.2) and by external sources of errors, such as object movement during the examination5. Thus, the exact position measured will depend on the TOF difference (step 2.4). One technique to achieve a good time resolution...

Positron Emission Tomography is a non-invasive imaging technique used for obtaining digital images of the inner tissues and organs of the body. Various non-invasive techniques exist that allow one to obtain images and information on the internal workings of a patient such as Computer Axial Tomography (TAC) and Magnetic Resonance Imaging (MRI). Both give good spatial resolution and are additionally used for applications in anatomic and physiologic studies. Although comparatively PET gives less spatial resolution, it provides more information concerning the metabolism occurring in the zone of interest. PET is widely used to obtain functional and morphological information; its main clinical applications are in the fields of oncology, neurology and cardiology. Also, PET images can help physicians give better diagnoses, e.g., establish tumor treatment planning.
The basic working principle of PET systems is the detection of two photons or gamma rays coming from a positron-electron annihilation pair, both flying in opposite directions towards the detectors, which commonly consist of scintillator crystals coupled with PMTs. The scintillator crystals transform gamma radiation into visible light, which travels to a PMT which converts the light signal to an electrical pulse via a photoelectric process. Inside the PMT electronic devices called dynodes are present, which increase the magnitude of the electrical charge before sending it to a read-out system. These two detected photons were created when a positron (positively charged electron) emitted by an isotope fluid, which was injected into the bloodstream of the body, annihilates with an electron in the body. The read-out system measures in coincidence the arrival time of the two back-to-back photons with respect to a time reference and further it substrates both times to obtain the difference. The system uses this time difference to calculate the space position where the radiation source emitted both photons, and thus where the electron-positron annihilation occurred.
Some features of PET systems must be defined to optimize the quality of the image and to increase spatial and time resolution. One feature to consider is the Line of Response (LOR), defined as the distance that the two photons travel after the annihilation process. Another feature to consider is the Time of Flight (TOF). The quality of the images also depends on external features, mainly the bodily organs and the patient&#39;s movements during the treatment session1. The isotopes used in PET systems are called Beta+ emitters. These isotopes have a short half-life (on the order of seconds). They are produced in particles accelerators (cyclotrons) when stable elements are bombarded with protons or deuterons causing nuclear reactions. Such reactions transform the stable elements into unstable isotopes, such as C-11, N-13, O-15, F-18 among others2.
There are two types of PET. (1) Conventional: this uses the TOF information only to identify the line along which the annihilation occurred, but it is unable to determine the origin place of the two photons. It requires additional analytical or iterative reconstruction algorithms to estimate this. (2) TOF PET: utilizes the TOF difference to locate the annihilation position of the emitted positron. The time resolution is used in the reconstruction algorithm as a kernel for a localization probability function3.
Our main objective is to demonstrate the primary functions of PET, which is used to locate a radiation source in space. The principal scope of the PET system set proposed here is to provide a basic PET construction guide for the academic public, and to explain, in a simple way, its main properties.

<table border="0" cellpadding="0" cellspacing="0" width="675">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">Low threshold Discriminator</td>
			<td style="width:152px;">CAEN</td>
			<td style="width:119px;">N845</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Logic Units</td>
			<td>Lecroy</td>
			<td>365AL</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Time delay</td>
			<td>CAEN</td>
			<td>N108A</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Oscilloscope</td>
			<td>Tektronic</td>
			<td>TDS3014C</td>
			<td></td>
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			<td height="21" style="height:21px;">Quad Scaler and preset counter</td>
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			<td>N1145</td>
			<td></td>
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			<td>Lecroy</td>
			<td>2228</td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;">PMT&#8217;s</td>
			<td>Hamamatsu</td>
			<td>H5783p</td>
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			<td style="width:119px;">1403</td>
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			<td height="21" style="height:21px;">GPIB Interface</td>
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			<td height="21" style="height:21px;">Scintillator Crystals</td>
			<td>Bicron</td>
			<td>408</td>
			<td>1cm x 2cm x 5cm&#160;</td>
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			<td height="21" style="height:21px;">Power Supply</td>
			<td>Agilent</td>
			<td>E3631</td>
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			<td height="21" style="height:21px;">Na 22 Radioactive Source</td>
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			<td style="width:119px;"></td>
			<td>activiti 2&#956;Ci</td>
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			<td height="21" style="height:21px;">Software LabView 7.1</td>
			<td>National intruments</td>
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</table>

a basic positron emission tomography system constructed to locate a radioactive source in a bi-dimensional space

A simple Positron Emission Tomography (PET) prototype has been constructed to fully characterize its basic working principles. The PET prototype was created by coupling plastic scintillator crystals to photomultipliers or PMT&#39;s which are placed at opposing positions to detect two gamma rays emitted from a radioactive source, of which is placed in the geometric center of the PET set-up. The prototype consists of four detectors placed geometrically in a 20 cm diameter circle, and a radioactive source in the center. By moving the radioactive source centimeters from the center the system one is able to detect the displacement by measuring the time of flight difference between any two PMT&#39;s and, with this information, the system can calculate the virtual position in a graphical interface. In this way, the prototype reproduces the main principles of a PET system. It is capable to determine the real position of the source with intervals of 4 cm in 2 lines of detection taking less than 2 min.

Two main results are achieved with this PET system. First: an efficient synchronization between visual effects of the virtual radioactive source when moving the real radioactive sample. With this program, users have control of the acquisition time, the number of repetitions in the same position, the variation of the interval around the acquisition data mean, among others. Second: the construction of a simple structure of coincidence logic to obtain the time difference between two signals,...

Watch this Scientific Journal Video about A Basic Positron Emission Tomography System Constructed to Locate a Radioactive Source in a Bi-dimensional Space at JoVE.com

A Basic Positron Emission Tomography System Constructed to Locate a Radioactive Source in a Bi-dimensional Space

We present a simple but well-constructed Positron Emission Tomography (PET) system and elucidate its basic working principles. The goal of this protocol is to guide the user in constructing and testing a simple PET system.

A simple Positron Emission Tomography (PET) prototype has been constructed to fully characterize its basic working principles. The PET prototype was ...

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