MR Accreditation Programs - E. Jackson

Transcription

1 MRI Accreditation Programs: An Overview of Each and Specifics of One Edward F. Jackson, PhD Department of Imaging Physics 1 Diagnostic - MRI Safety and Accreditation Educational Objectives At the conclusion of this presentation, the attendee should: understand the MIPPA Advanced Diagnostic Imaging Accreditation requirements and choices of accrediting organizations understand the current clinical and physics requirements of the modular ACR MRI accreditation i program understand the specific ACR program requirements for medical physicists / MR scientists, including CME requirements understand the testing requirements for both the large and small ACR MRI accreditation phantoms, and understand the annual physics testing requirements for the ACR MR accreditation program 2 Requirements of MIPPA Requirements of MIPPA MIPPA Medicare Improvements for Patients and Providers Act (passed in 2008) Section 135(a) calls for advanced diagnostic imaging accreditation of all facilities that bill the technical component of diagnostic MRI, CT, and nuclear medicine such as PET services Facilities must be accredited by January 1, 2012 However, all facilities does not include hospitals Currently, the Centers for Medicare and Medicaid Services (CMS) specifically indicates that the advanced diagnostic imaging (ADI) accreditation can be provided by: The Joint Commission The The American College of Radiology Each of these accreditation programs has its own requirements 3 4 The Joint Commission The Joint Commission The Joint Commission provides Advanced Diagnostic Imaging accreditation as part of its program for accreditation of diagnostic imaging centers. Per Joint Commission posted information, providers already accredited by The Joint Commission do not need to be accredited (for ADI) until their current accreditation expires.* The ADI accreditation cost depends on the number of annual patient visits and number of sites (branches). Additional fees may be incurred for multiple modalities and sites.** * TJC online resource: Accreditation Handbook for Diagnostic Imaging Centers ** TJC online resource: Accreditation for Your Freestanding Imaging Center 5 With respect to Standard EC The organization manages safety and security. At a minimum, the organization manages safety risks in the magnetic resonance environment associated with the following: Patients t who may experience claustrophobia, anxiety, or emotional distress Patients who may require urgent or emergent medical care Metallic implants and devices Ferrous objects entering the MRI environment TJC online resource: Changes to Standards & EPs for Advanced Imaging Requirements 6 1

2 The Joint Commission The Joint Commission With respect to Standard EC The organization manages medical equipment risks. The organization identifies activities and frequencies to maintain the reliability, clarity, and accuracy of the technical quality of diagnostic images produced. With respect to Standard EC The organization inspects, tests, and maintains medical equipment. The organization maintains the reliability, clarity, and accuracy of the technical quality of diagnostic images produced. No specific additional information is available regarding the specifics of The Joint Commission ADI accreditation for MRI. It is stated that All initial surveys conducted under the Advanced Diagnostic Imaging Services survey option will be conducted on an unannounced basis. * TJC online resource: Changes to Standards & EPs for Advanced Imaging Requirements 7 * TJC online resource: Accreditation Handbook for Diagnostic Imaging Centers 8 Intersocietal Commission for the Accreditation of Magnetic Resonance Laboratories (ICAMRL) created in 2000 As of February 2012, the new name is ICA MRI Offers accreditation in the areas of: Cardiovascular MRI Breast MRI Body MRI (chest (non-cardiac), abdomen, pelvis, extremity) Musculoskelatal MRI Neurological MRI and MRA The ICA MRI accreditation process does not require purchase of a specific phantom. However, through the application process participating laboratories must provide documentation of their ongoing, comprehensive quality assessment programs. The ICA MRI standards are available online at: Part I of the standard addresses: Supervision and Personnel (training and CME requirements) Medical Director Medical Staff Technical Director Technical Staff Support Services (clerical, nursing, transport, etc.) Physical Facilities Examination Interpretation, Reports, and Records Safety and Patient Confidentiality

3 Part I of the standard addresses (continued): Instrumentation Devices must be FDA approved MRI unit must be capable of performing multiplanar T1, T2, and STIR sequences with a FOV large enough to consistently image all relevant anatomy in the region of interest The equipment specifications and performance must meet all state, federal, and local requirements (db/dt, B 0,max, max SPL, max SAR) Multiple Sites Part I of the standard addresses (continued): Quality Assurance There must be a quality assurance program in the MR laboratory Quality Assurance Committee role Quality control tests, standards, thresholds, timelines, and results review Quality control tests should be performed according to the manufacturer s performance standards by the MR technologist, service engineer, medical physicist, or qualified expert on a timely basis Quality assurance documentation must be maintained at the MR laboratory and made available to all personal Part I of the standard addresses (continued): Quality Assurance The quality assurance program must consist of MR system installation acceptance testing and major upgrade acceptance testing Acceptance testing must be performed as part of the system installation and after major upgrades, prior to patient clinical use. The manufacturer s representative, service engineer, or the MR siteappointed medical physicist, or qualified expert, should perform the acceptance testing. Acceptance testing should include, but is not limited to: B 0 homogeneity, gradient and RF calibration, resonance frequency, slice thickness and accuracy, image quality (SNR for all coils, spatial resolution, artifacts, image uniformity, geometric distortion, monitor/processor QC) 15 Part I of the standard addresses (continued): Quality Assurance Written report of the acceptance tests, signed and dated, must be maintained Routine (daily and periodic) QC tests Proper function of audible and visual patient safety equipment Center frequency tests SNR Image uniformity Artifact assessment Deviations from established thresholds must be documented and corrective action taken where appropriate 16 Part I of the standard addresses (continued): Quality Assurance Periodic preventive maintenance (PM) service is recommended for each MR scanner PM quality control assessment should include, but is not limited to: SNR, B 0 homogeneity, RF calibration of all coils, spatial resolution, artifact assessment General equipment inspection, e.g., RF coil cables, RF shielding, etc. A complete report of PM, QC tests, and service records must be maintained and must be signed and dated by the person(s) performing the tests. Ancillary equipment must be included as part of the QA program 17 Part II of the standard addresses: Indications (body, cardiovascular, MSK, neurological, breast, MRA) Techniques Positioning and coil selection Appropriate protocol & optimization of pulse sequence(s) for the indication Utilization of appropriate software, workstations, techniques, and measurements A complete, written description of each protocol must be maintained, including acquisition details, contrast agent administration, filming, etc. Procedure Volumes Technical and Interpretative Quality Assessment Technical / Administrative Quality Assessment, including appropriate use criteria Interpretative Quality Assessment over-reads, correlation with outcomes, etc

4 Application Case Studies EFFECTIVE 1/1/12 Applicant facilities must submit six (6) total case studies for each MRI unit. Cases must represent each area of testing that is performed on the scanner, i.e., Cardiovascular MRI, Breast MRI, Body MRI [chest (noncardiac), abdomen, pelvis, extremity], Musculoskeletal l l MRI, Neurological l MRI, MRA. For example, if your facility is applying in two of the following testing areas you must submit 3 cases for each testing area; if your facility is applying in one testing area, you must submit 6 case studies total. In addition, the printed or electronic final reports and MRI Scan Parameter Forms must be submitted. Cases must have been obtained within the 12 months prior to the date of submission 19 Application IAC agreement Copies of various site policies Acceptance testing results (at installation and/or after major upgrade). All acceptance tests completed after January 5, 2011 must include submission of the QC test t results with the phantom images. 5 days of daily quality control tests with the results and the phantom images Preventative maintenance (PM) report (performed six months prior to application submission) Two (2) months of QA meeting minutes (for facilities applying for reaccreditation) Note: All phantom images must be submitted on CD or DVD with a DICOM viewer ACR Accreditation Programs ACR MRI Accreditation Overview Purpose: to set quality standards for practices and to help continuously improve the quality of patient care to be educational in nature Beneficial for accrediting body and site ACR assists sites improve practice Site obtains PR benefit Sites assist ACR in gathering information about MRI practices. History 1996 ACR MR program accreditation launched 2001 Initial MR QC Manual released 2004 QC Manual update T magnets included 2006 Documentation of QC and annual system performance evaluation required 2008 Modular program introduced ACR MRI Modular Program ACR Accreditation Process Overview Whole body (brain, C-spine, L-spine spine, knee) 23 Head Spine Musculoskeletal Body MR angiography Cardiac Every unit must apply for all modules routinely performed on that unit for a facility to be accredited. Note: Breast MR accreditation is included in the Breast Imaging Accreditation program Submission materials: Scanner information Most recent annual medical physicist performance report Personnel qualifications and CME information Clinical images for each module submitted Phantom images with associated site scanning data form Most recent quarter of QC data $$$$ 24 4

5 ACR CME Requirements ACR MRAP Cost Accreditation First Unit Accreditation Second Unit Repeat Add units or module (mid-cycle) $2400 (1-4 modules) $2600 (5 modules) $2800 (6 modules) $2300 (1-4 modules) $2500 (5 modules) $2700 (6 modules) $800 per unit for clinical or phantom $1600 for both $1600 per unit Clinical Images Clinical Images Examination Choices for MRAP by module: - see MRI Accreditation Program Requirements file on ACR website, p. 12 of 15 Examination Choices for MRAP by module: - see MRI Accreditation Program Requirements file on ACR website, p. 12 of ACR Accreditation Process Overview Clinical Images Evaluated for 1) appropriate pulse sequence and contrast, 2) filming technique (if appropriate), 3) anatomic coverage and imaging planes, 4) spatial resolution, 5) artifacts, and 6) appropriate labeling of images Must be submitted in DICOM format on CD with embedded viewer. Requirements for viewer must are provided in the ACR MRI Clinical Image Quality Guide

6 ACR Accreditation Process Overview ACR Accreditation Process Overview Phantom Images Discussed in detail on subsequent slides Acquired on ACR MR Accreditation Phantom using specified T 1 - and T 2 -weighted protocols plus the site s T 1 - and T 2 - weighted protocols (for brain imaging). Must be submitted in DICOM format on CD-ROM (w/o embedded viewer; no image compression) Evaluated for 1) geometric accuracy, 2) high contrast spatial resolution, 3) slice thickness accuracy, 4) slice position accuracy, 5) signal uniformity, 6) ghosting, 7) low contrast detectability. 31 Annual MRI System Performance Evaluation Mustbe performed by a medical physicist / MR scientist Includes MRAP phantom scans and tests required for weekly QC and specific tests of: Magnetic field homogeneity Slice thickness and position accuracy Radiofrequency coils SNR all coils Uniformity all volume coils Soft-copy displays (monitors) Should also provide an assessment of MR safety issues at the facility 32 ACR MR Accreditation Phantom ACR Phantom Scan Documentation Contains information on: Phantom position Pulse sequences to be used Filming and data preparation instructions Large Phantom: $1050 Small Phantom: $ 780 (Ortho) (as of 2/10/2012) Sent to site with Full Application Available from the ACR ACR Phantom Scan Documentation Alignment of the ACR Phantom Contains information on: Test analysis Performance criteria Common reasons for failure Sent to site with Full Application Available from the ACR 45 Alignment is important! Center phantom in head coil use foam, stack of paper, paper towels, or cardboard Make sure phantom is straight use bubble level Make sure phantom is centered SI, LR & AP make localizer images in all 3 planes use grid to check centering Record position for future use 46 6

7 ACR Phantom Scans ACR Accreditation Process Overview Sagittal Localizer TE/TR=20/200ms, 25 cm FOV, 256x256, 1 20-mm, 1 NEX, 0:56 ACR T1 Axial Series TE/TR=20/500ms, 25 cm FOV, 256x256, 11 5-mm slices (graphically prescribed), 1 NEX, 2:16 ACR T2 Axial Series TE1/TE2/TR=20/80/2000ms, 25 cm FOV, 256x256, 11 5-mm slices (same locations as for ACR T1 series), 1 NEX, 8:56 + Site T1 and T2 Axial Brain Series 47 #1 #7 #8 #5 #9 #10 #11 #1) Slice thickness and position, geometric accuracy, high contrast resolution #5) Geometric accuracy #7) Percent image uniformity, ghosting #8-11) Low contrast object detectability, and slice position (in #11) 48 Geometric Accuracy Slice Position ACR T1 True Dimension: 190 mm True Dimension: 148 mm ACR T1 & T2 Slice 1 Slice 5 Set WW & WL to min, then raise WL until 1/2 water is dark (mean) Set WW to mean and WL to 1/2(mean) 49 Sag Loc Criterion: ± 2 mm Slice 1 Slice 11 Criterion:<5mm 50 Slice Thickness Slice Thickness ACR T1 & T2 Slice 1 Two 10:1 ramps Magnify image by 2-4x. Define two ROIs, one on each ramp. Obtain average intensity from the two ROIs. Measurements: lower level to ½ average set window width to minimum measure lengths of top and bottom ramps calculate slice thickness Criterion: 5.0±0.7 mm

8 ACR T1 & T2 Slice 1 High Contrast Spatial Resolution Magnify by 2-4x. Use UL for horizontal resolution and LR for vertical resolution. Must be able to resolve 1.0 mm holes vertically and horizontally. UL Spatial Resolution Matrix: Registration with Phantom Resolution Holes mm LR Image Matrix Image compliments of Geoff Clarke, PhD Low Contrast Detectability Low Contrast: High vs. Low Field ACR T1 & T2 Slices 8-11 Slice 8: 1.4% Slice 9: 2.5% Slice 10: 3.6% Slice 11: 5.1% 1.5 T 0.3 T 1.5T Criterion 9 spokes 3.0T Criterion 37 spokes 55 Slice 11 - ACR T1 series 56 ACR T1 & T2 Slice 7 Percent Image Uniformity (~1 cm 2 ) ACR T1 Ghosting Slice 7 Ghost ratio = (top+bottom) - (left+right) (2 large ROI) Large ROI ( cm 2 ) percent integral uniformity = ( high low ) 1.5T ( high low) 3.0T Criterion: PIU 87.5% Criterion: PIU 82% 57 Criterion: ROIs ~ 10 cm 2 with ~4:1 length:width 58 8

9 Ghosting Window and level to make sure ROIs are in background noise! (Warping of image space due to gradient nonlinearity corrections.) Common Problems and Artifacts Potential Causes of Geometric Accuracy Failures Poor phantom positioning - relatively common problem Poor gradient calibration B o inhomogeneity Ferromagnetic objects in magnet Poor magnet shimming Gradient non-linearity (not appropriately corrected) Inappropriate receiver bandwidth Poor eddy current compensation Combination of two or more of above 61 Rotation (in-plane) 62 Poor Positioning Poor Positioning Poor Positioning Rotation (through-plane, RL) Rotation (through-plane, AP)

10 Sources of Geometric Distortion Spatial Accuracy System Limitations Poor B o homogeneity Linear scale factor errors in the gradient fields Field distortion due to induced eddy currents Nonlinearities of the gradient fields Object-Induced Chemical shift effects Magnetic susceptibility variations (patient induced) Be sure to make sagittal measurements at the center of the phantom (or as close as possible to the center) Air Bubbles Low Acquisition Bandwidth When a large air bubble is present in the phantom, geometric distortion measurement may have to be taken along diagonal instead of vertical. Note distortion as well as increased susceptibility artifacts Air Bubbles Spatial Resolution Matrix: Registration with Phantom Resolution Holes 16 khz 8 khz Image Matrix Image compliments of Geoff Clarke, PhD 10

11 High-Contrast Spatial Resolution Image Intensity Uniformity Common causes of failure; Incorrect FOV or matrix size Poor gradient calibrations Excessive filtering (smoothing) Poor eddy current compensation Gradient amplifier instability Big ROI ~ 195 cm 2 (19,500 mm 2 ) Small ROI s ~ 1 cm 2 (100 mm 2) Max Signal Min Signal ACR phantom - Slice # Image Intensity Uniformity Percent Signal Ghosting Common causes of failure: Poor phantom centering in coil (usually in AP direction) Ghosting Motion or vibration Mechanical failure in head coil Note: Uniformity becomes poorer with increasing B o (especially above 2 T) because of dielectric field focusing phenomenon (aqueous phantom). Must pass on slice #7 of ACR T1-weighted axial series. Ghost signal is measured and reported as percentage of the signal in the true image Excessive ghosting in other images may be counted as Unacceptable Artifact Phase Ghosting Ghosting is Nonspecific Phase Readout GHOST NOISE GHOST Instability in MRI signal from pulse to pulse Phantom motion Loose connections or bad cable Partial failure of radiofrequency coils or gradient subsystem Pulse sequence calibration error Eddy currents in Fast Spin Echo series NOISE 75 Image compliments of Geoff Clarke, PhD 76 11

12 Ghosting Low Contrast Detectability ACR T1 & T2 Ghosting may obscure otherwise visible LCD spokes Slice 8: 1.4% Slice 9: 2.5% Slice 10: 3.6% Slice 11: 5.1% 77 Image compliments of Geoff Clarke, PhD 78 Low Contrast Detectability DC Offset Artifacts Some common causes of failure: Incorrectly positioned slices Contrast based on partial volume averaging Tilted phantom Incorrect slice thickness Ghosting Inadequate SNR Large artifact off to side. NEX=1; frequency shifted Image compliments of Geoff Clarke, PhD Susceptibility Artifacts Details of the ACR MRI QC Manual Small inclusions in LCD insert can make analysis difficult

13 MRI QC Manual Overview Current Version: 2004 Radiologist s Section Describes requirements and the role in a QA program Technologist s Section Outlines the recommended daily and weekly QC tests Physicist s / MRI Scientist s Section Suggestions for setting up a QC program Outlines recommended annual equipment performance tests 83 Quality Assurance Manual Should contain the following: Responsibilities and procedures for QC testing. Records of the most recent QC tests. A description of the orientation program procedures for use and maintenance of the equipment. MRI techniques to be used. Precautions in place to protect the patient. Proper maintenance of records, including records of testing, equipment service, and QA meetings. Procedures for cleaning and disinfection. 84 Radiologist s Responsibilities Radiologist s Responsibilities (cont.) To ensure adequate training and continuing education in MRI To provide an orientation program for technologists To ensure that an effective quality control program exists for all MRI procedures To select the technologist to be the primary quality control technologist To ensure that appropriate test equipment and materials are available to perform the technologist s QC tests. 85 To arrange staffing and scheduling so that QC tests can be carried out. To provide feedback to the technologists. To select a qualified lifidmedical physicist ii or MRI scientist. i To review the technologist s test results To oversee or designate a qualified individual to oversee the safety program. To ensure that records are properly maintained and updated in the MRI QC procedures manual. 86 Technologist s Responsibilities Technologist s Responsibilities Daily (weekly*) MR image QC procedures QC of hard and soft copy images Routine visual inspection of equipment Note: Effective May 2, 2002, the performance of daily QC tests is NOT required. All daily tests mentioned in the QC Manual are now required at least weekly (but daily testing is encouraged). Medical Physicist/MR Scientist interactions: Physicist assures correct implementation an execution of the QC procedures Physicist reviews QC notebook at least annually (quarterly preferred) Radiologist interactions: Radiologist informs technologist about image quality problems Radiologist decides whether or not patient studies can continue Radiologist participates in the initial assessment of image quality and regularly monitors the QC results in the intervals between annual reviews

14 Medical Physicist s Responsibilities Write purchase specifications Perform acceptance testing and establish baseline QC measurements Determine action limits for measured parameters Setup daily/weekly QC tests Perform annual MRI equipment performance reviews Details of the Technologist s Responsibilities Technologist s Section Technologist s Section Identification of the designated QC technologist(s) Maintenance of the QC Notebook QC policies and procedures Data forms where QC procedure results are recorded Notes on QC problems and corrective action(s) Document QC data review Alternative phantoms and procedures Action limits Technologist s Section Technologist s Section Routine tests using ACR phantom and ACR T 1 -weighted head scan: Center frequency (daily/weekly) Geometric and positioning accuracy (daily/weekly) y) Image quality (daily/weekly) High contrast resolution Low contrast object detectability Artifact evaluation (daily/weekly) Plus: Processor sensitometry (weekly) Physical and mechanical inspection (weekly) min 14

15 Technologist s Section Technologist s Section Daily (Weekly) Record central frequency and transmit gain (attenuation) settings for the ACR axial T 1 series. Check position accuracy by ensuring central grid structure is within 2 mm of the center of the image Verify geometric accuracy by ensuring length (sagittal localizer image) and vertical/horizontal diameter (axial slice #5) measures are within 2 mm of true values Verify high contrast resolution (vertical and horizontal) using T 1 series axial slice #1 Verify low contrast object detectability levels using T 1 series axial slice #8, 9, 10, or 11 (as determined by physicist/mr scientist) 95 Daily (Weekly) (cont) Assess level of image artifacts in axial T 1 series Phantom should appear circular There should be no ghost images in the background or overlying the phantom image There should be no streaks or artifactual bright or dark spots in the image There should be no unusual or new features in the image. 96 Daily Axial ACR T1 Series Daily Tests - Transmitter Gain and Frequency Spin-echo sequence TE/TR=20/500ms Slice thickness / gap = 5/5 mm 11 slices graphically prescribed from sagittal localizer FOV = 25 cm Matrix: 256x256 1 average (NEX, NSA, etc.) Scan time: 2:16 min 97 During the prescan for the T1 series, the scanner determines the appropriate transmitter gain (or attenuation) and transmit (center) frequency. On some scanners, these values are easily obtained at the end of prescan and/or from the series text page. On other scanners, these values will need to be obtained from special options (see service engineer). The transmit gain (attenuation) value and center frequency value should be recorded daily. 98 Daily Tests - Geometric Accuracy Daily Tests - High Contrast Spatial Resolution True Dimension: 190 mm True Dimension: 148 mm Magnify by 2-4x. Use UL for horizontal resolution and LR for vertical resolution. Must be able to resolve 1.0 mm holes vertically and horizontally. UL mm Slice 5 Set WW & WL to min, then raise WL until 1/2 water is dark (mean) Set WW to mean and WL to 1/2(mean) 99 Sag Loc Criteria: ± 2 mm 100 LR 15

16 Daily Tests - Low Contrast Detectability Daily Tests - Assessment of Artifacts Count and record the number of spokes in the slice determined by the Medical Physicist or MR Scientist. (Typically slice 11for low field and slice 8 or 9 for high field.) Action criteria: Change of more than 3 spokes (or as determined by QC procedure). 101 Look at all slices from the localizer and axial T1 series. Modify window width and level to look for ghosting artifacts and radiofrequency interference artifacts. Note any change in image quality relative to baseline scans. 102 Technologist s QC Log - Daily Tests Weekly Tests - Processor QC Weekly Tests SMPTE Pattern Gray Level Ring Weekly Tests - Processor QC Weekly Tests - Processor QC Weekly Hard Copy QC Tests: Display SMPTE test pattern. Visually examine the SMPTE pattern (0/5% and 95/100% patches). Measure the optical density (OD) of the 0, 10, 40, and 90% gray level patches with a densitometer. Plot OD values on the Laser Film QC Chart. Inspect film for streaks, uneven densities, and other artifacts

17 Weekly Tests - Visual Inspection RF Shielded Room Door At least weekly visual inspection tests: Check patient table, patient communication, patient panic buttons, transport, alignment, and system indicator lights Check RF room integrity (particularly RF doors) Check that emergency cart, safety lights, signage, and patient monitors (and supplies) are present and in working order Check that all RF coils are present and in apparent good working condition (no frayed cables, etc.) The RF door fingers provide good electrical contact of the shielded door and the rest of the Faraday cage shield. If the fingers are damaged, as they will inevitably be, the effectiveness of the shield decreases and will ultimately give rise to RF interference artifacts (or cause them on an adjacent scanner!). RF Coil Weekly Checks Be sure to check all cables on RF coils, particularly high use and/or flexible coils. Any suspicious coils, cables, or connector boxes should be reported immediately to your service organization and/or vendor s service engineer. 110 Technologist s QC Summary Technologist runs QC runs on a daily (weekly) basis, and records the results in the QC logbook. Some Details of the Medical Physicist s / MR Scientist s Responsibilities If any test result exceeds the appropriate action limit (established by Medical Physicist/MR Scientist), repeat QC test. If still fails, notify service (and log service call). Action criteria are usually set based on 10 or more repeated measurements

18 Medical Physicist/MR Scientist Responsibilities Performs acceptance tests New systems before first patient scan Following any major hardware or software upgrade Acquires baseline QC data acquisition and establishes action limits Central frequency Transmitter gain / attenuation Geometric accuracy High contrast resolution Low contrast object detectability Artifact analysis 114 Medical Physicist/MR Scientist Responsibilities Laser camera QC Establish operating levels (in consultation with laser film system service engineer) Acquire baseline data (using SMPTE test pattern) Corrective actions Determination of whether problem lies in the camera, processor, and/or MR system 115 Annual Physics Tests Magnetic field homogeneity Slice position accuracy Slice thickness accuracy RF coil checks Signal-to-noise ratio (all coils) Image uniformity (volume coils) Interslice RF interference Phase stability (ghosting) Soft copy displays (monitors) Assessment of MR safety program Medical Physicist/MR Scientist Responsibilities 116 Magnetic Field Homogeneity Ideal Homogeneity Good Homogeneity Poor Homogeneity FWHM o o o Denotes a totally uniform magnetic field. All signal is at resonant frequency, o. Fourier transform of signal produces a Lorentzian peak in well-shimmed magnet 117 FWHM Magnet field homogeneity can be characterized using FWHM of resonance peak Magnetic Field Homogeneity Magnetic Field Homogeneity One vendor s head equivalent phantom. Insert sphere can be used for homogeneity test. (Remove sphere from cylindrical loader first. Place at isocenter in head coil.) With sphere in head coil, use manual prescan. Adjust center frequency twice to determine the full width at half maximum of the spectrum

19 Magnetic Field Homogeneity Magnetic Field Homogeneity Phase images from GRE sequences with 10ms difference in TE s Phase and Unwrapped Phase Images The change in phase across the phantom is proportional to the inhomogeneity of the magnetic field. Harmonic Coefficients given for Z1, Z2, Z3, Z4, Z5, Z6, X, Y, ZX, ZY, X2-Y2, XY, Z2X, Z2Y, ZXY, etc. LVshim Report Exam 50196, Series 2, Image 1 (Fri Jan 24 20:35: ) Scan Bandwidth d = 200 Hz Field of View = 50 cm Sampling Diameter = 22 cm Inhomogeneity 3.19 Hz (0.050 ppm) Magnetic Field Homogeneity Slice Position Accuracy Either the FWHM technique (on a given spherical phantom) or the phase difference technique can be used to assess homogeneity if possible at a given site. Slice Position Slice Spacing Alternative: Use the service engineer s report on homogeneity for your site records of homogeneity. SLICE #1 SLICE #11 Crossed wedges should be of equal length if position and spacing are accurate (and phantom is not tilted!) Measurements: lower level to ½ average set window at minimum measure lengths of top and bottom ramps calculate slice thickness Slice Thickness Site & Equipment Data B o Homogeneity Slice Position Accuracy - MRI Equipment Performance Evaluation Site: Date: MRAP Number: Serial Number: Equipment: MRI System Manuafacturer: Model : Processor Manufacturer : Model: PACS Manufacturer: Model: ACR MRAP Phantom Number used: 1. Magnetic Field Homogeneity Method Used (check one): Spectral Peak Phase Difference Other (describe) Measured Homogeneity: Diameter of Spherical Homogeneity Volume (cm) (ppm) 2. Slice Position Accuracy From Slice Positionss #1 and #11 of the ACR Phantom: Wedge (mm) =+ = - =+ = Slice Location #1 Slice Location #11 Slice Thickness Accuracy 3. Slice Thickness Accuracy From Slice Position #1 of the ACR Phantom: Slice Thickness Top Calculated slice (fwhm in mm) Thickness (mm) Bottom 124 Duplicate these forms so they will be available for repeated use. 19

20 Volume RF Coil Measurements Volume Coils - SNR, Uniformity, and Ghosting 126 Must assess SNR, uniformity, and ghosting ratio for every volume coil. ACR Phantom Slice #7 Uniformity performance criteria: PIU 90% percent integral uniformity = ( high low ) ( high low) SNR (no fixed criteria) (Mean Signal ROI) / (SD of Noise ROI) Percent Signal Ghosting Left Right Top Bottom Mean Signal 127 Phased-Array Coils Phased-Array Coils Breast Phased Array Wrist Phased Array Torso Phased Array Example of a particular vendor s C-T-L spine phased array coil QC phantom Head-Neck-Spine Phased Array Surface RF Coil Measurements % Image Uniformity Signal-to-Noise Percent Signal Ghosting Volume Coil Data Max Signal Min Signal Mean Signal SD of Background Signal Ghost Signal Mean Signal Background Signal Maximum Signal-to-Noise Surface Coil Data Maximum signal SD of Background Signal

21 -2 MR Accreditation Programs - E. Jackson Volume Coil Calculated Values: Uniformity SNR Ghosting 4. RF Coil Performance Evaluation A. VOLUME RF COIL - RF Coil Description: Date: Phantom Description: Pulse Sequence: Type: TR: TE: flip angle degrees FOV: cm 2 Matrix: BW: khz ; NSA Slice thickness mm; spacing mm TX attenuation (or gain) Data Collected: Mean Maximum Minimum Background Noise Ghost Signal Signal Signal Signal Standard Signal Deviation Calculated Values: Signal-to-Noise Percent Percent Ratio Image Uniformity Signal Ghosting Requires precision luminance meter Soft Copy Displays Surface Coil Calculated Value: Maximum SNR - B. RF SURFACE COIL - RF Coil Description: Date: Phantom Description: Pulse Sequence: Type: TR: TE: FOV: cm 2 Matrix: BW: khz ; NSA Slice thickness mm; spacing mm TX attenuation (or gain) Maximum Noise Standard Maximum Signal-to- Signal Deviation Noise Ratio Image uniformity distribution OK? Image ghosting OK? HARD COPY IMAGE: Window width Window level Four tests: Maximum and minimum luminance Luminance uniformity Resolution (SMPTE) Spatial accuracy (SMPTE) Several copies of this page may be required to report on all RF coils. 133 Max luminance (WL/WW min): 90 Cd/m 2 Min luminance: <1.2 Cd/m 2 Luminance uniformity: Each of the luminance values obtained at the four corners of the screen should be within 30% of the maximum value measured at the center (WL/WW min). Resolution: Use SMPTE 100% contrast patterns (see QC manual, p. 117). Spatial accuracy: Use SMPTE grid pattern (see QC manual, p. 117). 134 Soft Copy Displays RF Slice Interference Soft ftcopy Displays Review of Routine QC Program - 90 % 80 % 5. Interslice RF Interference Phantom Description: Pulse Sequence: Type: TR: TE: FOV: cm 2 Matrix: BW: khz ; NSA Number of slices 100% S eries S lice S igna l- Number Gap to-noise (m m ) Ratio 1 2 Measured SNR % 0% 25% 50% 75% 100% Inte r-slice Gap (perce nt of slice thickne ss) 6. Soft Copy Displays Monitor Description: Maximum Luminance: Cd m 2. Minimum Luminance: Cd m -2. Luminance Uniformity: Average of values obtained in four corners of screen: Cd m -2. Luminance measured in center of screen: Cd m -2. Percent difference: % (Center Average Corners)/(Center) x 100% < 30% 7. Evaluation of Site s Technologist QC Program Set up and positioning accuracy: (daily) 4) 5) Center Frequency: (daily) 6) Transmitter Attenuation or Gain: (daily) 7) Geometric Accuracy Measurements: (daily) 8) Spatial Resolution Measurements: (daily) 9) Low Contrast Detectability: (daily) 10) Film Quality Control (weekly) Visual Checklist: (weekly) Summary Medical Sheet MRI Equipment Evaluation Summary Site Report Date: System MRAP # Survey Date: MRI System Manufacturer Model: Physicist/MRI Scientist: Signature: Equipment Evaluation Tests Pass / Fail 1. Magnetic Field Homogeneity: 2. Slice Position Accuracy 3. Slice Thickness Accuracy 4. RF Coils Performance Coils Signal-to-Noise Ratio a. Volume b. Volume Coils Image Uniformity c. Volume Coils Ghosting Ratios d. Surface Coils Signal-to-Noise Ratio 5. Inter-slice RF Interference 6. Soft copy displays M di l Physicist s i or MRI Scientist s t Recommendations for Quality Improvement: ACR MRI QC Program Summary Technologist Performs daily (weekly) tests to assess image quality using the ACR phantom Performs weekly tests of hard copy output Miti Maintains QC notebook!! tb Medical Physicist / MR Scientist Runs baseline tests of system performance Sets action limits for daily ACR phantom tests Performs annual system performance tests Reviews all QC program data annually

22 ACR MRI QC Program Summary Radiologist Ultimately responsible for all QA for the facility All measurements, problems reported, and actions required to resolve the problems must be recorded for review, as must all preventive maintenance and repair records from the vendor or service organization