(K) Page 41-45 A Simple Low Cost (35-39)


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(K) Page 41-45 A Simple Low Cost (35-39)

  1. 1. World Journal of Nuclear Medicine, Volume 6, Number 1, January 2007 A simple low cost phantom for the quality control of SPECT cameras Perkins AC, Clay D, Lawes SC Dept of Medical Physics, Nottingham University Hospitals, Nottingham, UK Correspondence: Prof. Alan C Perkins Academic Medical Physics Medical School Queen's Medical Centre Nottingham NG7 2UH, UK Email: alan.perkins@nottingham.ac.uk Abstract Key words: SPECT phantom, SPECT quality control, low costphantom WorldJNuclMed2007;6:35-39 Introduction This technical note describes the design, construction and initial use of a low cost phantom for the assessment of SPECT cameras using materials commonly available in most departments and requiring minimal construction facilities. The design was based on the use of different sized syringes as hot or cold rod sources held in an acrylic back plate. A constructional diagram is provided together with initial imaging example and suggested use for the assessment of parameters such as spatial resolution, limits of lesion detection and contrast. This phantom may be used in departments with minimal scientific support and would be ideal for regular quality control and image evaluation in units where other more expensive phantoms are not available or within developing countries. It is also envisaged that this phantom could be used with a range of radionuclides in experimental situations for the assessment of detection characteristics when a new clinical SPECT procedureisbeingintroduced. The quality assurance of nuclear medicine imaging equipment has been recommended by a number of highly regarded institutions and organisations (1-5). One important area of measurement is the assessment of the quality of SPECT images. Ideally assessment of these parameters can be undertaken using purpose built phantoms that can be either purchased commercially or built in house. However the cost of such phantoms may be prohibitive, for example at the time of writing a standard SPECT phantom can be purchased for the cost of $1,800 in the United States. There is therefore a need for low cost phantoms that can be easily constructed and used on a routine basis if the quality control of SPECT systems is to be more widely carried out. This technical note describes the design and initial use of such a phantom. The remit for the design of a phantom was that it could be easily constructed with simple low cost materials that would be readily available to most nuclear medicine departments. The phantom design was based on the use of syringes of different sizes to create discrete cavities of either hot or cold regions that could be used to assess image quality. Technical drawings are provided in Figure 1. The syringes were supported in universal syringe “blind hubs” glued in to a back plate and arranged in a circle around a central point such that the cross sectional images would provide a series of circular regions as previously obtained from more complex phantoms. The back plate was supported by a base plate, the complete assembly forming an L shape. The plates were constructed from 10mm thick clear acrylic plastic.Anylon handle was added to the top to minimise the risk of dropping the phantom when containing radioactivity. The phantom was constructed in the local Medical Physics workshop and tested in the nuclear medicine department. 6 TM BD Plastipak syringes (BD Drogheda, Ireland) having volumes of 1, 2.5, 5, 10, 20 and 60ml were used to give 6 different cross sectional diameters ranging from 4mm to 30mm. The syringes were filled with Tc-99m at a concentration of approximately 5MBq/ml. The phantom was then placed in a plastic tank that was filled with water MaterialsandMethods Medical Physics 35
  2. 2. and covered with a lid. It was positioned on the scanning bed with the long axis of the syringes parallel with the long axis of the bed. Tomographic SPECT/CT images were recorded on a GE Millennium gamma camera fitted with Hawkeye (GE Medical Systems, Slough, UK). Images were recorded and displayed on a Hermes Nuclear Medicine Computer (Nuclear Diagnostics, Gravesend, UK) using standard clinical acquisition protocols with either filtered back projection or iterative image reconstruction. Aphotograph of the prototype phantom is given in Figure 2. Construction of the phantom was easy and could be completed within 1 day. Use within the camera room was straightforward. Syringes could be filled and reused, or disposed of as appropriate. When placed in a water tank the syringes could be used as ether hot or cold cylinders. Data acquisition was undertaken according to standard clinical protocols. Reconstructed transverse sectional images across the syringes showed circular regions of different size Results (Figure 3). Knowing the diameter of the syringes the resolution of the system could be evaluated. In the example given in Figure 3 the smallest diameter cylinder measuring 4mm in diameter is only just visible and is therefore only justatthelevelofdetection. In the initial experiment the phantom was used for the assessmentofthefollowingparameters: • Lesiondetectability • Imagecontrast/hotspot/coldspotresolution • Evaluation of the use of different reconstruction filtersonspatialresolution • Evaluationofattenuationandscattercompensation. Quality control is now mandatory practice for any diagnostic imaging department and may be the subject of review and audit procedures to ensure the appropriate standard of service (6,7). Such procedures would also be a requirement for any department wishing to achieve a level of formal accreditation. We have described the design, Discussion 25.0 10.0 25.0 130 130 60 degrees 10 mm 0 Front view Both holes tapped at 4.0 mm All holes drilled through, 10 mm diameter Figure 1a. Front plan of the back plate showing the position of drilled holes in10mm thick clear acrylictotakethesyringeblindhubs.Alldimensionsareinmm. Perkins AC, Clay D, Lawes SC World Journal of Nuclear Medicine, Volume 6, Number 1, January 2007 36
  3. 3. 10mm 130.0 Side view Figure 1b. Side view of the phantom showing the back plate and base plate made from 10mm thick clear acrylic.All dimensions in mm. Figure 1c. Design of the handle made from black nylon and fitted to the top of the back plate. All dimensions in mm. 10 mm 5.5mm 20.0mm 10.0mm 28.0mm Tappde at 4 mm Side view Top view World Journal of Nuclear Medicine, Volume 6, Number 1, January 2007 Perkins AC, Clay D, Lawes SC 37
  4. 4. Figure 2. Photograph of the phantom assembly holding 6 different sized syringes. Figure 3. Transverse fused SPECT/CT image showing Tc-99m activity within the syringes (colour) and the non-radioactive water filled tank with the base plate of the phantom at the bottom. Perkins AC, Clay D, Lawes SC World Journal of Nuclear Medicine, Volume 6, Number 1, January 2007 38
  5. 5. construction and initial use of an inexpensive phantom produced from materials commonly available in most departments and requiring minimal construction facilities. Use of such a phantom should make the assessment of SPECTimage performance more widely practicable. Assuming minimal workshop support an initial design of a plastic container, preferably with a lid and a series of hollow spheres that could be supported by a rod across the top was considered. However finding hollow spheres of different sizes (apart from a ping pong ball) was not straightforward. Filling and supporting these was also cumbersome, hence this approach was rejected. The use of different sized syringes between 1ml and 60ml was then considered to form a rod phantom. This design also had the advantage of minimising the manipulation of liquid sources since once the activity was drawn up into the syringe there was no further manipulation and this would therefore reduce the likelihood of contamination of rooms and equipment. Use of the syringes also simplifies the calculation of volumes of radioactive solutions for the estimation of specific activity or lesion contrast. Construction was simple and was achieved at a cost of approximately $15 US for the materials and $75 US for labour, representing a considerable saving on commercially available systems. It must be emphasised however that this phantom is not intended as a comprehensive quality control tool and an obvious limitation is that it does not have a section for image uniformity measurements. However this does represent a simple and economical means for introducing some routine measurements of image parameterswherealternativephantomsarenotavailable. The initial use of the phantom has been demonstrated, however further detailed measurements were not included as it is hoped that these will be undertaken by other departments investigating the applications of this phantom. A second phantom has been dispatched to the Medical Physics Department at the University of Malaya Medical Centre for more detailed independent evaluation in a different setting. It is envisaged that the phantom may be suitable for routine quality measurements to be undertaken on a weekly or monthly basis. SPECT images could be taken to assess the image spatial resolution and detection limits with particular regard to the effects of changing reconstruction variables. The phantom may be used with any liquid tracer for example Tc-99m, In-111, I-123 and I- 131 and this may be of value in experimental situations where a new or non-standard clinical procedure is being carried out. The total amount of activity in the order of 500MBq to 750MBq is suggested per experiment, i.e., similar to a radionuclide bone scan, although there is no reason why higher amounts of activity could not be used. The dilutions of activity in MBq /ml could be varied to give ratios from 2:1 to 10:1 between the rods and the background activity placed within the scanning tank to assess limits of detectability. It should be stressed that when adding radioactivity to the water in the tank to from a background level of activity it is suggested that a lid or covering is securely in place to prevent the possibility of contamination of the scanning bed. We would also suggest that the same phantom could be used with the syringes containing X-ray contrast for the simple assessment of X-ray CT images and the assessment of image offset on SPECT/CT and PET/CT systems 1. Rotating Scintillation camera SPECT acceptance testing and quality control. AAPM Report No.22 American Institute of Physics 1987. 2. National Electrical Manufacturers Association 2000 Recommendations for Implementing SPECT Instrumentation Quality Control. J Nucl Med 2000; 41:383389 3. National Electrical Manufacturers Association (NEMA). Performance Measurements of Scintillation Cameras. NEMA NU 1-2001. Washington: NEMA; 2001. 4. Quality Control of Nuclear Medicine Instruments. IAEA,Vienna,1991 5. IPEM 86: Quality Control of Gamma Camera Systems. Institute of Physics and Engineering in Medicine,York; 2003. 6. Nuclear Medicine Resources Manual. IAEA, Vienna, 2006. 7. Jarritt PH, Perkins AC, Woods SD. Audit of Nuclear Medicine Scientific and Technical Standards Nucl Med Commun 2004; 25:771-775. Reference World Journal of Nuclear Medicine, Volume 6, Number 1, January 2007 Perkins AC, Clay D, Lawes SC 39