Performance Testing of a Dual-Source CT Scanner
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Performance Testing of a Dual-Source CT Scanner James Kofler, Ph.D., Michael Bruesewitz, R.T. (R), Thomas Vrieze, R.T. (R), Lifeng Yu, Ph.D., Cynthia McCollough, Ph.D. Department of Radiology Mayo Clinic, Rochester, MN INTRODUCTION The dual-source (DS) CT scanner (Somatom Definition, Siemens Medical Solutions) introduced in 2006 represents a new paradigm in medical imaging. The ability to acquire CT data using two different x-ray sources during a single acquisition offers many new clinical applications, including dual-energy CT (bone removal, stone characterization, virtual non-contrast imaging, etc.), increased x-ray output for faster scanning of heavy patients, and improved temporal resolution for cardiac imaging. However, the capabilities of a DS scanner also introduce new challenges to the medical physicist for performance characterization of the system, primarily due to its increased complexity. This exhibit will present information on how the DS systems work and how to determine meaningful and practical physics tests for acceptance testing and routine quality assurance. Performance characterization that requires specialized equipment and non-standard access to the scanner features will not be addressed. Testing methods and suggestions for achieving ACR accreditation are presented. CONCLUSIONS Performance testing of DSCT scanners presents additional challenges to the medical physicist. There are many different scan configurations and options available and the physicist must determine which parameters are essential for characterizing and monitoring the clinical performance of the scanner. Additionally, there may be clinical configurations that cannot be readily tested using conventional techniques. This exhibit details the scan parameters that are currently tested at our institution. However, as the DS technology continues to mature, new features and options are likely to emerge. Our experience has shown that fairly significant changes in the available scanner settings can occur with relatively minor software upgrades, necessitating adjustments to clinical and testing protocols. Information gleaned from post-upgrade testing can be invaluable to appropriately implementing changes into the clinical protocols. In summary, performance testing and monitoring of rapidly developing imaging technologies can be very dynamic and the physicist responsible for oversight of such equipment must be prepared to incorporate new scan options into the testing paradigm in a meaningful and practical manner. References 1. Flohr TG, McCollough CH, Bruder H, Peterskila M, Gruber K, Suess C, Grasruck M, Stierstorfer K, Krauss B, Raupach R, Primak AN, Kuttner A, Achenback S, Becker CR, Kopp A, Ohnesorge B. First performance evaluation of a dual-source CT (DSCT) system. Eur Radiol 2006; 16:256-268. 2. Bruesewitz MR, McCollough CH, Braun NN, Primak AN, Fletcher JG, Schmidt B, Flohr T. Dual Energy Computed Tomography: How Does It Work and What Can It Do?, Educational Exhibit, RSNA 2007. 3. Johnson TR, Nikolau K, Wintersperger BJ, Leber AW, von Ziegler F, Rist C, Buhmann S, Knez A, Reiser MF, Becker CR. Dual-source CT cardiac imaging: initial experience. Eur Radiol. 2006 Jul;16:1409-15. 4. Johnson TR, Krauss B, Sedlmair M, Grasruck M, Bruder H, Morhard D, Fink C, Weckbach S, Lenhard M, Schmidt B, Flohr T, Reiser MF, Becker CR. Material differentiation by dual energy CT: Initial experience. Eur Radiol. 2007 Jun;17:1510-7. 5. American Association of Physicists in Medicine, Specification and Acceptance Testing of Computed Tomography Scanners, Report no. 39 (AAPM, New York, 1993). 6. McCollough CH, Zink, FE. Performance Evaluation of a Multi-slice CT System. Med. Phys. 26(11), November 1999. Figure 1. Photograph of a coverless Definition scanner showing the orthogonally positioned tube/detector systems. Table 1. Detector configurations* available on the DS scanner. What to Test? The large number of possible tube/detector configuration combinations available on the DS scanner presents a unique challenge to the medical physicist for acceptance testing and routine quality assurance measurements. This is compounded by the fact that some combinations are limited to only spiral or sequential acquisitions. This is especially problematic for CTDI measurements, where spiral acquisitions may not have a comparable sequential acquisition. Additionally, the second x-ray tube, typically referred to as the “B-tube”, can not be operated independently of the primary x-ray tube (the “A-tube”). This implies that the physicist must make reasonable assumptions in order to acquire clinically meaningful CTDI measurements on the system. When the detector configuration used for clinical applications cannot be matched for a CTDI measurement, the configuration with the next closest total detector collimation should be used, which is consistent with the requirements for ACR accreditation dose measurements. For DS CTDI measurements, the CTDI from the B-tube must be deduced by measuring the CTDI from the A-tube and the A+B-tubes (both tubes used simultaneously at the same kV). Alternatively, use of the service mode will allow B-tube-only scans, but this option may not be available to all users. The remainder of this exhibit lists scan parameters for various tests used for acceptance testing and routine quality assurance testing at our institution. Choice of tube current values is somewhat arbitrary, but should be within the clinically useful range and remain consistent for all future measurements. Detailed instructions for common tests is not provided here, as this information is widely available. 6-7 Additionally, tests that are independent of the CT scan parameters, such as table incrementation and positioning accuracy, laser light alignment, etc. will not be discussed. Acceptance Testing versus Routine Quality Assurance Measurements The purpose of acceptance testing is twofold: 1) to compare the performance metrics with expected values, provided either from the manufacturer or from published values; and 2) to establish baseline values for comparison with future measurements. Obtaining a complete set of performance metrics can be difficult, especially with newer technologies, such as the DS CT scanner. Therefore, focus should be placed on establishing a collection of baseline data that is representative of the current and potential clinical use of the system. Note that some scanner features and clinical usage are subject to change, which may make some existing data obsolete. In these cases, new baseline data should be established that reflect the new usage of the system. Routine quality assurance is the periodic monitoring of the scanner performance for comparison with baseline values to determine if the performance is changing over time. The goal of a routine quality assurance program is to discover any performance degradation before it is manifested in the clinical images. Routine quality assurance measurements are a subset of acceptance testing measurements. The philosophy at our institution is that the acceptance testing is very comprehensive. The subsequent routine quality assurance testing is minimal, consisting of only the most clinically relevant tests and those required by State regulations. UNIFORMITY Uniformity can be measured using standard procedures and module 3 of the ACR CT phantom (for head uniformity) or a 32 cm diameter water phantom (for body uniformity). At our institution, the most common clinical modes are included in the routine QA tests, with additional modes included for acceptance testing, as shown below. SLICE THICKNESS Slice thickness can be measured using module 1 of the ACR phantom. Radiation slice thickness can be measured using direct-exposure film or gafchromic film. The tables below list the scan parameters used at our institution. Note that the cardiac configuration is listed as a head mode because both the cardiac and head modes use the same head bowtie filter. This test can completed using module 1 of the ACR phantom or a water phantom. For ACR CT accreditation, a sequential detector configuration equivalent to the clinical spiral configuration should be used. The number of routine quality assurance measurements for the CT number of water at our institution is minimal because daily measurements of this metric are required by State regulations. All tests are performed using 120 kV unless otherwise indicated. DS CT SCANNER PERFORMANCE TESTS INTRODUCTION (continued) DS CT SCANNER PERFORMANCE TESTS (continued) CT NUMBER of WATER versus SLICE THICKNESS DOSE MEASUREMENTS (continued) Sequential Collimation Tube Factory Protocol Acceptance Testing Routine QA 64 x 0.6 12 x 1.2 A Only 24 x 1.2 BodyPCTSeq (Specials) AbdomenSeq (ABD) Body kVp 80, 100, 120, 140 AbdomenSeq (ABD) 2 x 1 1 x 10 1 x 5 ThoraxSeqHR (Thorax) AbdomenSeq (ABD) AbdomenSeq (ABD) A+B kVp 120 120 120 120 120 120 120 120 1 x 5 HeadRoutineSeq (Head) 120 120 1 x 10 HeadRoutineSeq (Head) 120 24 x 1.2 HeadRoutineSeq (Head) 80, 100, 120, 140 120 12 x 1.2 HeadRoutineSeq (Head) 120 12 x 0.6 HeadRoutineSeq (Head) 120 Head 24 x 1.2 64 x 0.6 A Only DS_CoronaryCTA_AdaptSeq DS_CaScSeq 80, 100, 120, 140 120 120 120 Cardiac A+B 14 x 1.2 (DE) DE_AbdomenSeq 140 (tube A)/80 (tube B) DS CT SCANNER PERFORMANCE TESTS (continued) LOW CONTRAST and HIGH CONTRAST RESOLUTION The scan parameters in the table below are for the low contrast and high contrast resolution measurements. All of the tests require spiral acquisitions. Our institution uses the ACR CT accreditation phantom (modules 2 and 4) but other phantoms with similar test objects could be used. The dual-energy mode is tested using an image created from combined A-tube and B-tube data (mixed image). For ACR CT accreditation, the CTDI measurement must represent the selected clinical scans, which are typically spiral acquisitions. If a sequential-equivalent detector configuration match does not exist, then the configuration with the next closest total collimation (number of detector rows used times the width of each row) must be used. For additional information on this point, see Exhibit PH1141: “Physics Testing for ACR CT Accreditation: Tips and Suggestions from Physics Reviewers.” To allow CTDI measurements for any detector configuration, Siemens Medical Solutions has recently developed a “Customer CTDI Measurement Tool.” The tool automatically converts a clinical spiral protocol to a sequential scan, conserving all relevant scan parameters, including the detector configuration. Using a “local service” option at the console, the user can recall the sequential scan and run the protocol for CTDI measurements. This feature will be part of all future software upgrades. This test is only performed during acceptance testing. All scans are performed using 120 kV and in body mode. The measured CTDI values should increase linearly with mAs across all mA settings. mR/mAs LINEARITY Sequential Collimation 24 x 1.2 mA Settings Scan Type 24 x 1.2 (Cardiac) A-only A+B 50, 100, 150, 200, 250, 300, 400, 500, 600 50, 100, 150, 200, 250, 300, 400, 500, 600 Constant Exposure Time (0.5 s) Sequential Collimation 24 x 1.2 Exposure Times (s) Scan Type 24 x 1.2 (Cardiac) A-only A+B 0.33, 0.5, 1.0 0.33, 0.5, 1.0 Constant mA (200 mA) Acceptance Testing & Routine QA Collimation 64 x 0.6 14 x 1.2 (DE-80 kV) Pitch Slice Thickness (mm) Rotation Time (s) Scan Type 64 x 0.6 (DS-Cardiac) 14 x 1.2 (DE-140 kV) 0.55 3 Spiral Spiral Spiral Spiral 0.5 0.33 0.5 0.5 5 1.0 0.2 0.55 5 5 CT NUMBER LINEARITY This test is performed using the same parameters for both acceptance testing and routine quality assurance. Only the primary scan modes are used for CT number linearity, which provides a reasonable verification of scanner calibration. Radiation Width (mm) Radiation Width (mm) Image Width (mm) Image Width (mm) Acceptance Testing Routine QA Acceptance Testing Routine QA 2 x 1 1 x 5 1 x 10 24 x 1.2 6 x 3 (DS-Cardiac) Rotation Time (s) Sequential Collimation 0.5 1.0 0.5 1.0 0.5 1.0 0.5 1.0 0.5 1.0 2 1 2 1 1 5 5 5 5 5 5 10 10 10 10 2.4 28.8 2.4 28.8 2.4 4.8 4.8 3 3 0.33 14 x 1.2 (DE-mixed) Image Width (mm) Image Width (mm) Pitch Pitch 64 x 0.6 24 x 1.2 0.33 0.5 0.5 1.0 0.5 1.0 Rotation Time (s) Spiral Collimation 0.5 1.0 1.5 3 3 3 0.5 1.0 1.5 0.5 1.0 1.5 0.5 1.0 1.5 0.5 0.55 1.0 1.5 3 0.6, 0.75, 1, 1.5, 2, 3, 5 3 5 0.55 5 3 0.6, 1, 3, 5 3 3 1.5, 2, 3, 4, 5 3 3 3 3 1.0 1.5, 5 1.0 1, 5 CTDI MEASUREMENTS CTDI must be measured using a sequential scan mode. As shown in Table 1, not all detector configurations for spiral acquisitions have a sequential-equivalent configuration. Therefore, it may not be possible to measure CTDI for some clinically-used spiral detector configurations. Additionally, with the current clinical software, the B-tube cannot be tested independently of the A-tube. B-tube CTDI values can be calculated from a DS CTDI measurement by subtracting the CTDI measured for an A-tube-only acquisition with the same detector configuration and kVp. Note that the head mode must be used for the A-tube acquisition because the DS mode (cardiac) uses the head filter. Although not a direct measure of B-tube-only x-ray output, this method allows the physicist to determine if there are any significant changes in either x-ray tube. CTDI measurements should be acquired with the appropriate phantom: 16, 32, and 32-cm diameter CTDI phantoms for the head, cardiac, and body scans, respectively (even though the cardiac mode uses the head bowtie filter, CTDI should be measured in the body phantom). CTDI measurements should also be acquired at isocenter in air. The table below lists a reasonable set of detector configurations for CTDI measurements during acceptance testing and routine quality assurance. The rows highlighted in yellow are those used for determining the B-tube-only doses. System Rotation times: 0.33, 0.5, 1.0 s Gantry opening: 78 cm No gantry tilt Each tube/detector pair 80 kW generator 40 detectors/row (32 x 0.6 mm, inner; 8 x 1.2 mm outer) Double z-sampling with Z-FFS Tube voltages: 80, 100, 120, 140 kV Tube A (50 cm SFOV) Tube B (26.5 SFOV) B Detectors A Detectors Tube A (50 cm SFOV) Tube B (26.5 SFOV) B Detectors A Detectors Overview of a Dual-Source CT Scanner Dual source CT is a CT system where two x-ray sources and two data acquisition systems are mounted on the same x-ray gantry, positioned orthogonally to one another on the gantry. 1-4 (Figure 1). Each x-ray source is equipped with an separate high-voltage generator, allowing independent control of both the x-ray tube potential and tube current. The raw projection data are acquired simultaneously from the two x-ray sources, albeit with a 90° phase difference. The two data sets can be processed together or separately. Depending on how the data is acquired and processed, the system can be operated in one of several different modes, described as follows: Single source mode: The scanner functions as a conventional 64-slice CT scanner, for either body imaging (no additional beam filtration) or head imaging (using an additional head bowtie filter). Cardiac mode: Both tubes are used at the same mAs and kV to improve the temporal resolution. The head bowtie filter is also used for this mode to constrain the majority of the radiation dose to the central 30 cm of the patient, where the organ of interest (the heart) is located. Dual-source obese mode: Both tubes are operated at the same mAs and kV to effectively double the x-ray tube power from 80 kW (per tube) to 160 kW (when both tubes are used and the projection data summed prior to image reconstruction). Dual-Energy mode: Both tubes are used, but at different kV and different mAs settings to provide low- and high-energy images for dual-energy processing. The kV and mAs settings are contrained to values that meet the criteria necessary for dual-energy imaging. The detectors on the Definition scanner are both 32 channel systems and incorporate double-z sampling 1 , yielding a maximum of 64 sets of projection data per rotation per tube. Some modes and features are available only with optional software or hardware packages. Thus, a considerable amount of the increased testing complexity is due to the large number of detector configurations and slice thicknesses available on the system (Table 1). Sequential Collimation Rotation Time (s) Acceptance Testing Routine QA Slice Thickness (mm) 2 x 1 1 x 5 1 x 10 24 x 1.2 0.5 1.0 1 1 5 5 10 4.8 4.8 0.5 1.0 0.5 1.0 0.5 1.0 0.33 3 3 10 Spiral Collimation Rotation Time (s) Pitch Slice Thickness (mm) Pitch Slice Thickness (mm) 64 x 0.6 0.5 3 0.5 1.0 0.6, 0.75, 1, 1.5, 2, 3, 5* 1.0 1, 5* 14 x 1.2 (DE-140 kV) 14 x 1.2 (DE-80 kV) 6 x 3 (DS-Cardiac) 1.0 0.5 0.5 0.5 1.5 3 3 0.5 1.0 1.5 0.6, 1, 3, 5 3 24 x 1.2 0.5 1.0 1.5 0.55 3 2, 3, 4 3 5 0.55 5 0.55 5 0.55 5 0.33 0.2 5* 0.2 5* Acceptance Testing Routine QA 64 x 0.6 (DS-Cardiac) *5mm slices also acquired at 80, 100, and 140 kV. Sequential Collimation Rotation Time (s) Acceptance Testing Routine QA Acceptance Testing Routine QA Slice Thickness (mm) 2 x 1 1 x 5 1 x 10 24 x 1.2 0.5 1.0 1.0 1.0 1 5 10 2.4 5 Spiral Collimation Rotation Time (s) Pitch Slice Thickness (mm) Pitch Slice Thickness (mm) Acceptance Testing Routine QA Acceptance Testing Routine QA 20 x 0.6 1.0 0.8 5 1.0 5 64 x 0.6 64 x 0.6 (DE-140 kV) 0.33 0.5 1.0 64 x 0.6 (DE-80 kV) 0.5 0.5 1.0 5 1.0 5 1.0 5 5 5 0.7 0.7 5 5 0.7 0.7 Sequential Collimation Rotation Time (s) Slice Thickness (mm) 1 x 10 24 x 1.2 1.0 1.0 10 2.4 Spiral Collimation Rotation Time (s) Pitch Slice Thickness (mm) Pitch Slice Thickness (mm) 64 x 0.6 14 x 1.2 (DE-140 kV) 0.33 0.5 1.0 14 x 1.2 (DE-80 kV) 0.5 0.5 1.0 5 1.0 5 1.0 5 5 5 0.55 0.55 5 5 0.55 0.55 1.0 5 HEAD HEAD BODY BODY *Some modes may be available only with optional packages. 2D 12 x 0.6 mm 7.2 mm 2.4, 7.2 14 x 1.2 mm 28.8 mm 1.2, 2.4, 4.8, 7.2, 9.6, 14.4 6 x 0.3 mm 1.8 mm 3, 6, 9 1 x 5 mm 5.0 mm 5.0 1 x 10 mm 10.0 mm 10.0 2D-Perfusion 32 x 0.6 mm 19.2 mm .6, 1.2, 2.4, 4.8, 9.6, 19.2 24 x 1.2 mm 28.8 mm 1.2, 2.4, 4.8, 7.2, 9.6, 14.4, 28.2 10 x 1.2 mm 12.0 mm 10.0 2D-High Res Lung 2 x 1 mm 2.0 mm 1, 2 2D-Biospy/ Care Vision 1 x 5 mm 5.0 mm 5.0 1 x 10 mm 10.0 mm 10.0 24 x 1.2 mm 28.8 mm 4.8 12 x 1.2 mm 14.4 mm 2.4, 4.8 6 x 1.2 mm 7.2 mm 1.2, 2.4 Care Bolus 1 x 10 mm 10.0 mm 10.0 2D-Neuro 6 x 3 mm 18.0 mm 3, 6, 9 12 x 1.2 mm 14.4 mm 1.2, 2.4, 4.8, 7.2, 14.4 3D Biopsy 24 x 1.2 mm 28.8 mm 1.2, 2.4, 4.8, 5, 10 3D-Cardio 32 x 0.6 mm 19.2 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 6 24 x 1.2 mm 28.8 mm 1.5, 2, 3, 4, 5, 6 3D-Perfusion 32 x 0.6 mm 19.2 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 10 24 x 1.2 mm 28.8 mm 1.5, 2, 3, 4, 5, 6, 7, 8, 10 3D-Ultrahigh Res 8 x 0.6 mm 4.8 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 10 Spiral 32 x 0.6 mm* 19.2 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 10 24 x 1.2 mm 28.8 mm 1.5, 2, 3, 4, 5, 6, 7, 8, 10 10 x 0.6 mm* 6.0 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 10 Cardio Spiral 32 x 0.6 mm* 19.2 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5 24 x 1.2 28.8 mm 1.5, 2, 3, 4, 5 Dual Energy Spiral 32 x 0.6 mm* 19.2 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 10 14 x 1.2 mm 16.8 mm 1.5, 2, 3, 4, 5, 6, 7, 8, 10 10 x 0.6 mm* 6.0 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 10 Neuro Spiral 10 x 0.6 mm 6.0 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 10 20 x 0.6 mm* 12.0 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 10 Mode* Detector Configuration Total Collimination Available Slices Sequential Modes Spiral Modes 2D 12 x 0.6 mm 7.2 mm 2.4, 7.2 14 x 1.2 mm 28.8 mm 1.2, 2.4, 4.8, 7.2, 9.6, 14.4 6 x 0.3 mm 1.8 mm 3, 6, 9 1 x 5 mm 5.0 mm 5.0 1 x 10 mm 10.0 mm 10.0 2D-Perfusion 32 x 0.6 mm 19.2 mm .6, 1.2, 2.4, 4.8, 9.6, 19.2 24 x 1.2 mm 28.8 mm 1.2, 2.4, 4.8, 7.2, 9.6, 14.4, 28.2 10 x 1.2 mm 12.0 mm 10.0 2D-High Res Lung 2 x 1 mm 2.0 mm 1, 2 2D-Biospy/ Care Vision 1 x 5 mm 5.0 mm 5.0 1 x 10 mm 10.0 mm 10.0 24 x 1.2 mm 28.8 mm 4.8 12 x 1.2 mm 14.4 mm 2.4, 4.8 6 x 1.2 mm 7.2 mm 1.2, 2.4 Care Bolus 1 x 10 mm 10.0 mm 10.0 2D-Neuro 6 x 3 mm 18.0 mm 3, 6, 9 12 x 1.2 mm 14.4 mm 1.2, 2.4, 4.8, 7.2, 14.4 3D Biopsy 24 x 1.2 mm 28.8 mm 1.2, 2.4, 4.8, 5, 10 3D-Cardio 32 x 0.6 mm 19.2 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 6 24 x 1.2 mm 28.8 mm 1.5, 2, 3, 4, 5, 6 3D-Perfusion 32 x 0.6 mm 19.2 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 10 24 x 1.2 mm 28.8 mm 1.5, 2, 3, 4, 5, 6, 7, 8, 10 3D-Ultrahigh Res 8 x 0.6 mm 4.8 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 10 Spiral 32 x 0.6 mm* 19.2 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 10 24 x 1.2 mm 28.8 mm 1.5, 2, 3, 4, 5, 6, 7, 8, 10 10 x 0.6 mm* 6.0 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 10 Cardio Spiral 32 x 0.6 mm* 19.2 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5 24 x 1.2 28.8 mm 1.5, 2, 3, 4, 5 Dual Energy Spiral 32 x 0.6 mm* 19.2 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 10 14 x 1.2 mm 16.8 mm 1.5, 2, 3, 4, 5, 6, 7, 8, 10 10 x 0.6 mm* 6.0 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 10 Neuro Spiral 10 x 0.6 mm 6.0 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 10 20 x 0.6 mm* 12.0 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 10 Mode Detector Configuration Total Collimination Available Slice Thickness Sequential Modes Spiral Modes Spiral Collimation Rotation Time (s) Pitch Slice Thickness (mm) Pitch Slice Thickness (mm) 64 x 0.6 64 x 0.6 (DS-Cardiac) 0.5 0.5 1.0 5 5 0.55 5 0.55 0.33 3 0.2 3 0.2 14 x 1.2 (DE - mixed) 1.0 5 Acceptance Testing Routine QA HEAD mode BODY mode HEAD mode BODY mode HEAD mode BODY mode HEAD mode BODY mode HEAD mode BODY mode
Transcript of Performance Testing of a Dual-Source CT Scanner
Performance Testing of a Dual-Source CT ScannerJames Kofler, Ph.D., Michael Bruesewitz, R.T. (R), Thomas Vrieze, R.T. (R), Lifeng Yu, Ph.D., Cynthia McCollough, Ph.D.
Department of RadiologyMayo Clinic, Rochester, MN
INTRODUCTIONThe dual-source (DS) CT scanner (Somatom Definition, Siemens Medical Solutions) introduced in 2006 represents a new paradigm in medical imaging. The ability to acquire CT data using two different x-ray sources during a single acquisition offers many new clinical applications, including dual-energy CT (bone removal, stone characterization, virtual non-contrast imaging, etc.), increased x-ray output for faster scanning of heavy patients, and improved temporal resolution for cardiac imaging. However, the capabilities of a DS scanner also introduce new challenges to the medical physicist for performance characterization of the system, primarily due to its increased complexity. This exhibit will present information on how the DS systems work and how to determine meaningful and practical physics tests for acceptance testing and routine quality assurance. Performance characterization that requires specialized equipment and non-standard access to the scanner features will not be addressed. Testing methods and suggestions for achieving ACR accreditation are presented.
CONCLUSIONSPerformance testing of DSCT scanners presents additional challenges to the medical physicist. There are many different scan configurations and options available and the physicist must determine which parameters are essential for characterizing and monitoring the clinical performance of the scanner. Additionally, there may be clinical configurations that cannot be readily tested using conventional techniques. This exhibit details the scan parameters that are currently tested at our institution. However, as the DS technology continues to mature, new features and options are likely to emerge. Our experience has shown that fairly significant changes in the available scanner settings can occur with relatively minor software upgrades, necessitating adjustments to clinical and testing protocols. Information gleaned from post-upgrade testing can be invaluable to appropriately implementing changes into the clinical protocols. In summary, performance testing and monitoring of rapidly developing imaging technologies can be very dynamic and the physicist responsible for oversight of such equipment must be prepared to incorporate new scan options into the testing paradigm in a meaningful and practical manner.
References1. Flohr TG, McCollough CH, Bruder H, Peterskila M, Gruber K, Suess C, Grasruck M, Stierstorfer K,
Krauss B, Raupach R, Primak AN, Kuttner A, Achenback S, Becker CR, Kopp A, Ohnesorge B. First performance evaluation of a dual-source CT (DSCT) system. Eur Radiol 2006; 16:256-268.
2. Bruesewitz MR, McCollough CH, Braun NN, Primak AN, Fletcher JG, Schmidt B, Flohr T. Dual Energy Computed Tomography: How Does It Work and What Can It Do?, Educational Exhibit, RSNA 2007.
3. Johnson TR, Nikolau K, Wintersperger BJ, Leber AW, von Ziegler F, Rist C, Buhmann S, Knez A, Reiser MF, Becker CR. Dual-source CT cardiac imaging: initial experience. Eur Radiol. 2006 Jul;16:1409-15.
4. Johnson TR, Krauss B, Sedlmair M, Grasruck M, Bruder H, Morhard D, Fink C, Weckbach S, Lenhard M, Schmidt B, Flohr T, Reiser MF, Becker CR. Material differentiation by dual energy CT: Initial experience. Eur Radiol. 2007 Jun;17:1510-7.
5. American Association of Physicists in Medicine, Specification and Acceptance Testing of Computed Tomography Scanners, Report no. 39 (AAPM, New York, 1993).
6. McCollough CH, Zink, FE. Performance Evaluation of a Multi-slice CT System. Med. Phys. 26(11), November 1999.
Figure 1. Photograph of a coverless Definition scanner showing the orthogonally positioned tube/detector systems.
Table 1. Detector configurations* available on the DS scanner.
What to Test?The large number of possible tube/detector configuration combinations available on the DS scanner presents a unique challenge to the medical physicist for acceptance testing and routine quality assurance measurements. This is compounded by the fact that some combinations are limited to only spiral or sequential acquisitions. This is especially problematic for CTDI measurements, where spiral acquisitions may not have a comparable sequential acquisition. Additionally, the second x-ray tube, typically referred to as the “B-tube”, can not be operated independently of the primary x-ray tube (the “A-tube”). This implies that the physicist must make reasonable assumptions in order to acquire clinically meaningful CTDI measurements on the system. When the detector configuration used for clinical applications cannot be matched for a CTDI measurement, the configuration with the next closest total detector collimation should be used, which is consistent with the requirements for ACR accreditation dose measurements. For DS CTDI measurements, the CTDI from the B-tube must be deduced by measuring the CTDI from the A-tube and the A+B-tubes (both tubes used simultaneously at the same kV). Alternatively, use of the service mode will allow B-tube-only scans, but this option may not be available to all users. The remainder of this exhibit lists scan parameters for various tests used for acceptance testing and routine quality assurance testing at our institution. Choice of tube current values is somewhat arbitrary, but should be within the clinically useful range and remain consistent for all future measurements. Detailed instructions for common tests is not provided here, as this information is widely available.6-7 Additionally, tests that are independent of the CT scan parameters, such as table incrementation and positioning accuracy, laser light alignment, etc. will not be discussed.
Acceptance Testing versus Routine Quality Assurance Measurements
The purpose of acceptance testing is twofold: 1) to compare the performance metrics with expected values, provided either from the manufacturer or from published values; and 2) to establish baseline values for comparison with future measurements. Obtaining a complete set of performance metrics can be difficult, especially with newer technologies, such as the DS CT scanner. Therefore, focus should be placed on establishing a collection of baseline data that is representative of the current and potential clinical use of the system. Note that some scanner features and clinical usage are subject to change, which may make some existing data obsolete. In these cases, new baseline data should be established that reflect the new usage of the system.
Routine quality assurance is the periodic monitoring of the scanner performance for comparison with baseline values to determine if the performance is changing over time. The goal of a routine quality assurance program is to discover any performance degradation before it is manifested in the clinical images. Routine quality assurance measurements are a subset of acceptance testing measurements. The philosophy at our institution is that the acceptance testing is very comprehensive. The subsequent routine quality assurance testing is minimal, consisting of only the most clinically relevant tests and those required by State regulations.
UNIFORMITY
Uniformity can be measured using standard procedures and module 3 of the ACR CT phantom (for head uniformity) or a 32 cm diameter water phantom (for body uniformity). At our institution, the most common clinical modes are included in the routine QA tests, with additional modes included for acceptance testing, as shown below.
SLICE THICKNESSSlice thickness can be measured using module 1 of the ACR phantom. Radiation slice thickness can be measured using direct-exposure film or gafchromic film. The tables below list the scan parameters used at our institution. Note that the cardiac configuration is listed as a head mode because both the cardiac and head modes use the same head bowtie filter.
This test can completed using module 1 of the ACR phantom or a water phantom. For ACR CT accreditation, a sequential detector configuration equivalent to the clinical spiral configuration should be used. The number of routine quality assurance measurements for the CT number of water at our institution is minimal because daily measurements of this metric are required by State regulations. All tests are performed using 120 kV unless otherwise indicated.
DS CT SCANNER PERFORMANCE TESTSINTRODUCTION (continued) DS CT SCANNER PERFORMANCE TESTS (continued)
CT NUMBER of WATER versus SLICE THICKNESS
DOSE MEASUREMENTS (continued)
SequentialCollimationTube Factory Protocol
Acceptance Testing Routine QA
64 x 0.6
12 x 1.2A
Only
24 x 1.2BodyPCTSeq (Specials)
AbdomenSeq (ABD)
Bod
y
kVp
80, 100, 120, 140
AbdomenSeq (ABD)2 x 1
1 x 101 x 5
ThoraxSeqHR (Thorax)AbdomenSeq (ABD)AbdomenSeq (ABD)
A+B
kVp
120120120
120120120120120
1 x 5 HeadRoutineSeq (Head) 120 1201 x 10 HeadRoutineSeq (Head) 120
24 x 1.2 HeadRoutineSeq (Head) 80, 100, 120, 140 12012 x 1.2 HeadRoutineSeq (Head) 12012 x 0.6 HeadRoutineSeq (Head) 120
Hea
d
24 x 1.264 x 0.6
AOnly
DS_CoronaryCTA_AdaptSeqDS_CaScSeq 80, 100, 120, 140
120120
120
Card
iac
A+B 14 x 1.2 (DE) DE_AbdomenSeq 140 (tube A)/80 (tube B)
DS CT SCANNER PERFORMANCE TESTS (continued)
LOW CONTRAST and HIGH CONTRAST RESOLUTION
The scan parameters in the table below are for the low contrast and high contrast resolution measurements. All of the tests require spiral acquisitions. Our institution uses the ACR CT accreditation phantom (modules 2 and 4) but other phantoms with similar test objects could be used. The dual-energy mode is tested using an image created from combined A-tube and B-tube data (mixed image).
For ACR CT accreditation, the CTDI measurement must represent the selected clinical scans, which are typically spiral acquisitions. If a sequential-equivalent detector configuration match does not exist, then the configuration with the next closest total collimation (number of detector rows used times the width of each row) must be used. For additional information on this point, see Exhibit PH1141: “Physics Testing for ACR CT Accreditation: Tips and Suggestions from Physics Reviewers.” To allow CTDI measurements for any detector configuration, Siemens Medical Solutions has recently developed a “Customer CTDI Measurement Tool.” The tool automatically converts a clinical spiral protocol to a sequential scan, conserving all relevant scan parameters, including the detector configuration. Using a “local service” option at the console, the user can recall the sequential scan and run the protocol for CTDI measurements. This feature will be part of all future software upgrades.
This test is only performed during acceptance testing. All scans are performed using 120 kV and in body mode. The measured CTDI values should increase linearly with mAs across all mA settings.
mR/mAs LINEARITY
SequentialCollimation
24 x 1.2
mA SettingsScanType
24 x 1.2(Cardiac)
A-only
A+B
50, 100, 150, 200, 250, 300, 400, 500, 600
50, 100, 150, 200, 250, 300, 400, 500, 600
ConstantExposure
Time(0.5 s)
SequentialCollimation
24 x 1.2
Exposure Times (s)ScanType
24 x 1.2(Cardiac)
A-only
A+B
0.33, 0.5, 1.0
0.33, 0.5, 1.0
ConstantmA
(200 mA)
Acceptance Testing & Routine QA
Collimation
64 x 0.6
14 x 1.2(DE-80 kV)
PitchSlice
Thickness (mm)RotationTime (s)
ScanType
64 x 0.6(DS-Cardiac)
14 x 1.2(DE-140 kV)
0.55
3
Spiral
Spiral
Spiral
Spiral
0.5
0.33
0.5
0.5
51.0
0.2
0.55
5
5
CT NUMBER LINEARITY
This test is performed using the same parameters for both acceptance testing and routine quality assurance. Only the primary scan modes are used for CT number linearity, which provides a reasonable verification of scanner calibration.
RadiationWidth(mm)
RadiationWidth(mm)
ImageWidth(mm)
ImageWidth(mm)
Acceptance Testing Routine QA Acceptance Testing Routine QA
2 x 1
1 x 5
1 x 10
24 x 1.2
6 x 3(DS-Cardiac)
RotationTime(s)
SequentialCollimation
0.51.00.51.00.51.00.51.00.51.0
2 1 2 11
5 55 5 5 5
10 1010 10
2.428.8 2.4 28.8 2.4
4.84.8
3 30.33
14 x 1.2(DE-mixed)
ImageWidth(mm)
ImageWidth(mm)Pitch Pitch
64 x 0.6
24 x 1.2
0.33
0.5
0.5
1.0
0.5
1.0
RotationTime(s)
SpiralCollimation
0.51.01.5
333
0.5
1.0
1.50.51.01.50.51.01.50.5
0.55
1.01.5
30.6, 0.75, 1,1.5, 2, 3, 5
3
5 0.55 5
30.6, 1, 3, 5
33
1.5, 2, 3, 4, 53333
1.0 1.5, 5
1.0 1, 5
CTDI MEASUREMENTS
CTDI must be measured using a sequential scan mode. As shown in Table 1, not all detector configurations for spiral acquisitions have a sequential-equivalent configuration. Therefore, it may not be possible to measure CTDI for some clinically-used spiral detector configurations. Additionally, with the current clinical software, the B-tube cannot be tested independently of the A-tube. B-tube CTDI values can be calculated from a DS CTDI measurement by subtracting the CTDI measured for an A-tube-only acquisition with the same detector configuration and kVp. Note that the head mode must be used for the A-tube acquisition because the DS mode (cardiac) uses the head filter. Although not a direct measure of B-tube-only x-ray output, this method allows the physicist to determine if there are any significant changes in either x-ray tube. CTDI measurements should be acquired with the appropriate phantom: 16, 32, and 32-cm diameter CTDI phantoms for the head, cardiac, and body scans, respectively (even though the cardiac mode uses the head bowtie filter, CTDI should be measured in the body phantom). CTDI measurements should also be acquired at isocenter in air.
The table below lists a reasonable set of detector configurations for CTDI measurements during acceptance testing and routine quality assurance. The rows highlighted in yellow are those used for determining the B-tube-only doses.
SystemRotation times: 0.33, 0.5, 1.0 sGantry opening: 78 cmNo gantry tilt
Each tube/detector pair80 kW generator40 detectors/row (32 x 0.6 mm, inner; 8 x 1.2 mm outer)Double z-sampling with Z-FFSTube voltages: 80, 100, 120, 140 kV
TubeA
(50 cm SFOV)
TubeB
(26.5 SFOV)
BDetectors
ADetectors
TubeA
(50 cm SFOV)
TubeB
(26.5 SFOV)
BDetectors
ADetectors
Overview of a Dual-Source CT ScannerDual source CT is a CT system where two x-ray sources and two data acquisition systems are mounted on the same x-ray gantry, positioned orthogonally to one another on the gantry.1-4 (Figure 1). Each x-ray source is equipped with an separate high-voltage generator, allowing independent control of both the x-ray tube potential and tube current. The raw projection data are acquired simultaneously from the two x-ray sources, albeit with a 90° phase difference. The two data sets can be processed together or separately. Depending on how the data is acquired and processed, the system can be operated in one of several different modes, described as follows:
Single source mode: The scanner functions as a conventional 64-slice CT scanner, for either body imaging (no additional beam filtration) or head imaging (using an additional head bowtie filter).
Cardiac mode: Both tubes are used at the same mAs and kV to improve the temporal resolution. The head bowtie filter is also used for this mode to constrain the majority of the radiation dose to the central 30 cm of the patient, where the organ of interest (the heart) is located.
Dual-source obese mode: Both tubes are operated at the same mAs and kV to effectively double the x-ray tube power from 80 kW (per tube) to 160 kW (when both tubes are used and the projection data summed prior to image reconstruction).
Dual-Energy mode: Both tubes are used, but at different kV and different mAs settings to provide low- and high-energy images for dual-energy processing. The kV and mAs settings are contrained to values that meet the criteria necessary for dual-energy imaging.
The detectors on the Definition scanner are both 32 channel systems and incorporate double-z sampling1, yielding a maximum of 64 sets of projection data per rotation per tube. Some modes and features are available only with optional software or hardware packages. Thus, a considerable amount of the increased testing complexity is due to the large number of detector configurations and slice thicknesses available on the system (Table 1).
SequentialCollimation
RotationTime (s)
AcceptanceTesting
RoutineQA
Slice Thickness (mm)
2 x 1
1 x 5
1 x 10
24 x 1.2
0.51.0
1155
10
4.84.8
0.51.00.51.00.51.0
0.33 3 3
10
SpiralCollimation
RotationTime (s) Pitch
SliceThickness (mm) Pitch
SliceThickness (mm)
Routine QA
64 x 0.60.5 3
0.5 1.0 0.6, 0.75, 1,1.5, 2, 3, 5* 1.0 1, 5*
14 x 1.2(DE-140 kV)
14 x 1.2(DE-80 kV)
6 x 3(DS-Cardiac)
1.0
0.5
0.5
0.5
1.5 330.5
1.01.5
0.6, 1, 3, 53
24 x 1.20.51.01.5
0.55
32, 3, 4
3
5
0.55 5
0.55 5
0.55 5
0.33 0.2 5* 0.2 5*
Acceptance Testing Routine QA
64 x 0.6(DS-Cardiac)
*5mm slices also acquired at 80, 100, and 140 kV.
SequentialCollimation
RotationTime (s)
AcceptanceTesting
RoutineQA
AcceptanceTesting
RoutineQA
Slice Thickness (mm)
2 x 1 1 x 5
1 x 1024 x 1.2
0.51.01.01.0
15
102.4
5
SpiralCollimation
RotationTime (s) Pitch
SliceThickness (mm) Pitch
SliceThickness (mm)
Acceptance Testing Routine QA
Acceptance Testing Routine QA
20 x 0.6 1.0 0.8 5 1.0 5
64 x 0.6
64 x 0.6(DE-140 kV)
0.330.51.0
64 x 0.6(DE-80 kV)
0.5
0.5
1.0 51.0 51.0 5
5
5
0.7
0.7
5
5
0.7
0.7
SequentialCollimation
RotationTime (s)
Slice Thickness (mm)
1 x 1024 x 1.2
1.01.0
102.4
SpiralCollimation
RotationTime (s) Pitch
SliceThickness (mm) Pitch
SliceThickness (mm)
64 x 0.6
14 x 1.2(DE-140 kV)
0.330.51.0
14 x 1.2(DE-80 kV)
0.5
0.5
1.0 51.0 51.0 5
5
5
0.55
0.55
5
5
0.55
0.55
1.0 5
HEAD HEAD
BODY BODY
*Some modes may be available only with optional packages.
2D 12 x 0.6 mm 7.2 mm 2.4, 7.214 x 1.2 mm 28.8 mm 1.2, 2.4, 4.8, 7.2, 9.6, 14.46 x 0.3 mm 1.8 mm 3, 6, 91 x 5 mm 5.0 mm 5.01 x 10 mm 10.0 mm 10.0
2D-Perfusion 32 x 0.6 mm 19.2 mm .6, 1.2, 2.4, 4.8, 9.6, 19.224 x 1.2 mm 28.8 mm 1.2, 2.4, 4.8, 7.2, 9.6, 14.4, 28.210 x 1.2 mm 12.0 mm 10.0
2D-High Res Lung 2 x 1 mm 2.0 mm 1, 2
2D-Biospy/Care Vision
1 x 5 mm 5.0 mm 5.01 x 10 mm 10.0 mm 10.024 x 1.2 mm 28.8 mm 4.812 x 1.2 mm 14.4 mm 2.4, 4.86 x 1.2 mm 7.2 mm 1.2, 2.4
Care Bolus 1 x 10 mm 10.0 mm 10.0
2D-Neuro 6 x 3 mm 18.0 mm 3, 6, 912 x 1.2 mm 14.4 mm 1.2, 2.4, 4.8, 7.2, 14.4
3D Biopsy 24 x 1.2 mm 28.8 mm 1.2, 2.4, 4.8, 5, 10
3D-Cardio 32 x 0.6 mm 19.2 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 624 x 1.2 mm 28.8 mm 1.5, 2, 3, 4, 5, 6
3D-Perfusion 32 x 0.6 mm 19.2 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 1024 x 1.2 mm 28.8 mm 1.5, 2, 3, 4, 5, 6, 7, 8, 10
3D-Ultrahigh Res 8 x 0.6 mm 4.8 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 10
Spiral 32 x 0.6 mm* 19.2 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 1024 x 1.2 mm 28.8 mm 1.5, 2, 3, 4, 5, 6, 7, 8, 1010 x 0.6 mm* 6.0 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 10
Cardio Spiral 32 x 0.6 mm* 19.2 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 524 x 1.2 28.8 mm 1.5, 2, 3, 4, 5
Dual EnergySpiral
32 x 0.6 mm* 19.2 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 1014 x 1.2 mm 16.8 mm 1.5, 2, 3, 4, 5, 6, 7, 8, 1010 x 0.6 mm* 6.0 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 10
Neuro Spiral 10 x 0.6 mm 6.0 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 1020 x 0.6 mm* 12.0 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 10
Mode*Detector
ConfigurationTotal
Collimination Available Slices
Seq
uent
ial M
odes
Spi
ral M
odes
2D 12 x 0.6 mm 7.2 mm 2.4, 7.214 x 1.2 mm 28.8 mm 1.2, 2.4, 4.8, 7.2, 9.6, 14.46 x 0.3 mm 1.8 mm 3, 6, 91 x 5 mm 5.0 mm 5.01 x 10 mm 10.0 mm 10.0
2D-Perfusion 32 x 0.6 mm 19.2 mm .6, 1.2, 2.4, 4.8, 9.6, 19.224 x 1.2 mm 28.8 mm 1.2, 2.4, 4.8, 7.2, 9.6, 14.4, 28.210 x 1.2 mm 12.0 mm 10.0
2D-High Res Lung 2 x 1 mm 2.0 mm 1, 2
2D-Biospy/Care Vision
1 x 5 mm 5.0 mm 5.01 x 10 mm 10.0 mm 10.024 x 1.2 mm 28.8 mm 4.812 x 1.2 mm 14.4 mm 2.4, 4.86 x 1.2 mm 7.2 mm 1.2, 2.4
Care Bolus 1 x 10 mm 10.0 mm 10.0
2D-Neuro 6 x 3 mm 18.0 mm 3, 6, 912 x 1.2 mm 14.4 mm 1.2, 2.4, 4.8, 7.2, 14.4
3D Biopsy 24 x 1.2 mm 28.8 mm 1.2, 2.4, 4.8, 5, 10
3D-Cardio 32 x 0.6 mm 19.2 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 624 x 1.2 mm 28.8 mm 1.5, 2, 3, 4, 5, 6
3D-Perfusion 32 x 0.6 mm 19.2 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 1024 x 1.2 mm 28.8 mm 1.5, 2, 3, 4, 5, 6, 7, 8, 10
3D-Ultrahigh Res 8 x 0.6 mm 4.8 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 10
Spiral 32 x 0.6 mm* 19.2 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 1024 x 1.2 mm 28.8 mm 1.5, 2, 3, 4, 5, 6, 7, 8, 1010 x 0.6 mm* 6.0 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 10
Cardio Spiral 32 x 0.6 mm* 19.2 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 524 x 1.2 28.8 mm 1.5, 2, 3, 4, 5
Dual EnergySpiral
32 x 0.6 mm* 19.2 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 1014 x 1.2 mm 16.8 mm 1.5, 2, 3, 4, 5, 6, 7, 8, 1010 x 0.6 mm* 6.0 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 10
Neuro Spiral 10 x 0.6 mm 6.0 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 1020 x 0.6 mm* 12.0 mm 0.6, 0.75, 1, 1.5, 2, 3, 4, 5, 6, 7, 8, 10
ModeDetector
ConfigurationTotal
Collimination Available Slice Thickness
Seq
uent
ial M
odes
Spi
ral M
odes
SpiralCollimation
RotationTime (s) Pitch
SliceThickness (mm) Pitch
SliceThickness (mm)
64 x 0.664 x 0.6
(DS-Cardiac)
0.5
0.5
1.0 5
50.555
0.55
0.33 30.23
0.2
14 x 1.2(DE - mixed)
1.05
Acceptance Testing Routine QA
HEAD mode
BODY mode
HEAD mode
BODY mode
HEAD mode BODY mode
HEADmode
BODYmode
HEAD mode BODY mode
