An MRI quality assurance program includes several facets to ensure high quality images and appropriate clinical results. This includes quality control tests to detect equipment issues, a quality assurance committee to oversee the program, and tests of spatial resolution, low contrast detectability, slice thickness accuracy, and other parameters. Regular phantom scans and testing of center frequency, transmitter gain, and image uniformity allow issues to be identified before affecting patients. The program seeks to produce necessary and safe exams while minimizing risk and cost.

2. Introduction
 Magnetic resonance imaging (MRI) is now a mature and widely used imaging method.
 Achieving the full potential of MRI requires careful attention to quality assurance (QA),
both in regard to equipment performance and to the execution of imaging studies
 An effective QC program will not eliminate all problems but can allow for the
identification of problems before they seriously affect clinical results

3. Quality Assurance
 Quality assurance in MRI is a comprehensive concept that comprises all of the management
practices developed by the MR imaging team
 To ensure that:
 Every imaging procedure is necessary and appropriate to the clinical problem at hand
 The images generated contain information critical to the solution of the problem
 The recorded information is correctly interpreted and made available in a timely fashion
to the patient’s physician
 The examination results in the lowest possible risk, cost, and inconvenience to the patient
consistent with objectives above
 The QA program includes many facets, including efficacy studies, continuing education,
QC, preventive maintenance, safety, and calibration of equipment.

4. Quality assurance committee
 An essential part of the QA program is the QA Committee (QAC).
 This group has responsibility for oversight of the program, setting the goals and direction,
determining policies, and assessing the effectiveness of QA activities.
 The QAC should consist of the following:
 One or more radiologists
 A qualified medical physicist or MRI scientist
 A supervisory MR technologist
 Other radiology department personnel involved in caring for MRI patients, including a
nurse, desk attendant, medical secretary, or others
 Personnel outside the radiology department, including medical and paramedical staff such
as referring physicians. 5

5. Quality control
 Quality control is a series of distinct technical procedures that ensure the production
of a satisfactory product, in this case, high-quality diagnostic images.
 Four steps are involved:
 Acceptance testing to detect defects in equipment that is newly installed or has
undergone major repair
 Establishment of baseline performance of the equipment
 Detection and diagnosis of changes in equipment performance before they
become apparent in images
 Verification that the causes of deterioration in equipment performance have been
corrected

6. Acceptance testing
 Acceptance testing should take place before the first patient is scanned and after major
repairs. Major repairs include replacement or repair of the following subsystem components:
 Gradient amplifiers
 Gradient coils
 Magnet
 Radiofrequency (RF) amplifier
 Digitizer boards
 Signal processing boards
 A baseline check should be carried out on the MRI system as a whole and on additional
subsystems, such as repaired, replaced, or upgraded RF coils. All records should be kept at a
central location near the MRI scanner(s).

7. Phantoms
 The choice of phantom materials for use in quality assurance
phantoms should have:
 chemical and thermal stability,
 the absence of significant chemical shifts
 appropriate T1, T2 and proton density values which are within
the biological range
 At each operating field strength, the chosen MRI material should
exhibit the following characteristics:

8. Phantoms
 MRI phantom agents primarily consist of oils and water solutions of various
paramagnetic ions.

9. Phantoms
 The relaxation times are temperature and field strength dependent.
 The relaxation rates (inverse of relaxation times) are approx. linear with ion conc.
 For all measurements, scan conditions should be carefully recorded.
 All phantoms should be centered at the magnet iso-center unless otherwise
specified.

10. Widely used phantoms
 ACR Phantom (large and small)
 Eurospin Phantom
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11. Phantom problems
 Phantoms generally contain higher signals than humans and have a different
distribution of spatial frequencies, often with many high-contrast edges.
 The phantom geometry and materials may result in susceptibility effects and the
automatic shim may have trouble obtaining convergence.
 The filling materials may have atypical relaxation times with various consequences:
 Greater occurrence of coherence and stimulated echoes due to long T2, and greater
high spatial frequency signals in segmented sequences.

12. Phantom problems
 There are simple practical considerations to remember:
 allow the phantom fluid to settle
 let the phantom fluid reach thermal equilibrium with the environment, if
temperature-dependent
 avoid bubble formation
 minimize mechanical vibration
 It’s also important to remember that patients breathe, pulsate and fidget (the usual
cause of image quality problems) but that phantoms do not.
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13. Quality Control Testing Frequency

14. Setup and Table Position Accuracy
 To determine that the MRI scanner is performing patient setup, data entry, and pre-
scan tasks properly
 Test Procedure :-
 To ensure good reproducibility of the measurements, it is important to place the
phantom in the same position, properly centered and square within the coil, each
time.
 On the anterior side of the ACR large phantom (the side labeled “NOSE”), there is a
black line running in the head-to-foot direction to help align the phantom squarely
and a small positioning cross-line used to center the phantom

16. Scan technique
 The ACR sagittal localizer sequence should use the following parameters:
 For the large phantom: 1 slice, sagittal spin-echo, TR=200 ms, TE=20 ms, slice
thickness=20 mm, FOV=25 cm, matrix=256 × 256, NEX=1, scan time: 51-56
seconds (s).
 For the small phantom: 1 slice, sagittal spin-echo, TR=200 ms, TE=20 ms, slice
thickness=20 mm, FOV=12 cm, matrix=152 × 192, NEX=1, scan time: 32 s. If the
20-mm thick slice causes artifacts, a 10-mm slice may be used.

17. Data Interpretation
 If the positioning laser is properly calibrated
and the table positioning system functions
properly, the superior edge of the grid
structure should be at magnet iso-center
 If the location of the superior edge of the grid
structure is within ±5 mm, Table position
accuracy is OK.

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19. Center Frequency : (Resonance)
 Prior to the performance of any imaging protocol, it is essential that the MRI system is set on
resonance
 Resonance frequency checks are especially important for mobile units and resistive magnet
systems that undergo frequent ramping of the magnetic field
 Changes in the larmor freqeuncy reflect changes in the static B-field.
 Changes in the static B-field freq may be due to
 superconductor “run down” (typically on the order of 1ppm/day), e.g. 60Hz/day at 1.5T,
 changes in current density,
 due to thermal or mechanical effects,
 shim coil changes or
 effects due to external ferromagnetic materials.

20. Center Frequency : (Resonance)
 The effects of off-resonance primarily relate to system sensitivity and manifest as a reduction
in SNR.
 Phantom :The phantom is positioned in the center of the magnet (with all gradient fields
turned off), and the RF frequency is adjusted by controlling the RF synthesizer center
frequency to achieve signal .
 Scan: Display the central, sagittal slice through the ACR phantom acquired in the previous
test to prescribe slice locations of the axial T1-weighted series

21. Center Frequency : (Resonance)
 The recommended sequence for this acquisition for the large phantom is the ACR T1-
weighted axial series: 11 slices, spin echo, TR=500 ms, TE=20 ms, FOV=25 cm, slice
thickness=5 mm, slice gap=5 mm, matrix=256 × 256, NEX=1.
 for the small phantom is the ACR T1-weighted axial series: 7 slices, spin-echo, TR=500 ms,
TE=20 ms, FOV=12 cm, slice thickness=5 mm, slice gap=3 mm, matrix=152 × 192, NEX=1
 During the prescan, the system will automatically check the center frequency and set
the transmitter attenuation or gain.
 Limit:
 The drift rate for modern superconducting magnets should not exceed 1 ppm/day
during acceptance testing. (The value should be significantly less, typically less than
0.25 ppm/day, after 1 to 2 months of operation.)

22. Transmitter Gain or Attenuation
 After establishing the center frequency, the system acquires several signals while
varying the transmitter attenuation (or gain) level so that imaging can proceed using
the proper flip angles.
 Significant fluctuations in the transmitter attenuation (or gain) levels suggest
problems with the RF chain

23. Transmitter Gain or Attenuation
Test procedure
 Determine where the transmitter (TX) attenuation or gain is displayed on the scanner
console.
 Record the value displayed in column 5 on the Data Form for Weekly MRI Equipment
Quality Control
 If the change in decibels (dB) exceeds the action limits, report the problem to the
qualified medical physicist or MRI scientist
 Acceptance Criteria: Manually determined values of transmitter gain should agree to
within 5% with those determined automatically, and manual versus automatic
determinations of center frequency should agree within 10 Hz

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25. Image Uniformity
 It refers to the ability of the MR imaging system to produce a constant signal response
throughout the scanned volume when the object being imaged has homogeneous MR
characteristics
 Factors affecting image uniformity
 Static field inhomogeneity
 RF field non-uniformity
 Eddy currents
 Gradient pulse calibration
 Image processing

26. Method of measurement of Image Uniformity
 Phantom : a homogenous oil or ion-doped water
phantom
 To prevent RF penetration effects, the filler
material should be non-conducting
 Analysis : Pixels should be enclosed within a
centered geometric area which encloses approx
75% of phantom area.
 Percent Image Uniformity
(PIU) = {1 − (max−min) / (max+min) } x 100%
 Integral Uniformity ≥ 80%
PIU = 88.013708%. Close Figure to Continue

27. High-Contrast Spatial Resolution
 The high-contrast spatial resolution test assesses the scanner’s ability to resolve small
objects.
 It is a measure of the capacity of an imaging system to show separation of objects when
there is no significant noise.
 It is typically limited by acquisition matrix pixel size.
 The acq matric pixel size should not be confused with the display matrix pixel size in
which pixel interpolation or replication may have occurred.
 Traditionally, resolution has been quantified by PSF, LSF or MTF.

28. High-Contrast Spatial Resolution
 Required Equipment
 High-contrast resolution is checked with the ACR MRI accreditation phantom using
image slice 1 from the T1-weighted ACR axial series.
 Or any other phantom composed of either bar patterns or hole (or rod) arrays. Array
signal producing elements may be either round or rectangular in cross section.
 The pattern consist of alternating signal producing and non-signal producing areas set
apart from each other by width equal to the bar’s or hole’s width.
 Square bar patterns offer an adv. over round cross-section (hole) patterns in that the
smallest resolvable array element can be related to resolution in terms of lp/mm.

29. High-Contrast Spatial Resolution
 A typical phantom may consist of 5 signal producing elements and 4 spaces
through element sizes of 5, 3, 2, 1.5, 1.00, 0.75 and 0.5mm, although additional
increments may be used.
 The dimension in slice selection dir. (length) should be at least twice slice
thickness, i.e. 20mm length for 10mm ST

30. High-Contrast Spatial Resolution
 SCAN :
 Single or multi-slice acq is required.
 The phantom should be aligned perpendicular to ensure an adequate SNR.
 ANALYSIS : Resolution is expressed as the size of the smallest resolvable array
element or its equivalent in lp/mm when square bar patterns are used
 For the large phantom, the field of view and matrix size for the ACRT1-weighted axial
series are chosen to yield a nominal resolution of 1.0 mm in both directions. For both
directions in the axial T1-weighted ACR series, the measured resolution should be 1.0
mm or better.
 For the small phantom, the field of view and matrix size for the axial ACR series are
chosen to yield a resolution of 0.8 mm in both directions.

31. High-Contrast Spatial Resolution
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Typical appearance of well-resolved holes. Rows 2 through 4 of the UL array are
resolved, and columns 1 through 3 of the LR array are resolved. (Rows and columns
are numbered starting from the upper left corner of each array.)

32. LCD (low contrast detectability)
 The low-contrast detectability (LCD) test assesses the extent to which objects of
low contrast are discernible in the images
 Phantom:-ACR MRI accreditation phantom using image slices 8–11 from the
T1-weighted ACR axial series.

33. LCD (low contrast detectability)
 Test Procedure:
 Procedure to score the number of complete spokes seen in a slice:
 Display the slice to be scored as prescribed by the qualified medical physicist on the
Data Form
 Adjust the display window width and level settings.
 Visibility of the low-contrast objects require a fairly narrow window width and
careful adjustment of the level to best distinguish the objects from the background.
 Count the number of complete spokes seen. Begin counting with the spoke having
the largest diameter holes; this spoke is at 12 o’clock or slightly to the right of 12
o’clock and is referred to as spoke 1.

34. •For the large phantom, count clockwise from spoke 1 until a spoke is reached where one
or more of the holes are not discernible from the background.
•A spoke is complete only if all three of its holes are discernible. Count complete spokes,
not individual holes. Sometimes there will be one or more complete spokes of smaller
object size seen following a spoke that is not complete. Do not count these additional
spokes. Stop counting prior to the first incomplete spoke

35. a) Large phantom LCD insert images. Slice 11 (5.1% contrast) acquired on two different scanners, each
with proper slice positioning. The Right image is from a 1.5T scanner where all 10 spokes (each
spoke consisting of three test objects) are visible. left image is from slice 11 of a 0.3T scanner where
only seven complete spokes are visible.
b) Small phantom LCD insert images. The left image is slice 7 (5.1% contrast) from a 1T scanner, where
all 10 spokes are visible. The right image is also slice 7, but from a 0.3T scanner, where 7 spokes are
visible.
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37. Slice Thickness
 The slice thickness accuracy test assesses the accuracy with which a slice of
specified thickness is achieved.
 The prescribed slice thickness is compared with the measured slice thickness.

38. Slice Thickness
What Measurements Are Made:
 For this test the lengths of two signal ramps in slice 1 are
measured for both axial series.
 The ramps appear in a structure called the slice thickness
insert. For each axial series, the length of the signal ramps in
slice 1 is measured according to the following procedure:
 1. Display slice 1, and magnify the image by a factor of 2 to
4, keeping the slice thickness insert fully visible on the
screen.
 2. Adjust the display level so that the signal ramps are well
visualized. The ramp signal is much lower than that of
surrounding water, so usually it will be necessary to lower the
display level substantially and narrow the window.

39. Slice Thickness
What Measurements Are Made:
 3. Place a rectangular ROI at the middle of each signal
ramp as shown in Figure 11. Note the mean signal
values for each of these 2 ROIs, and then average
those 2 values together. The result is a number
approximating the mean signal in the middle of the
ramps.
 4. Lower the display level to half of the average ramp
signal calculated in step 3. Leave the display window
set to its minimum.

40. Slice Thickness
What Measurements Are Made:
 5. Use the on-screen length measurement tool of the
display station to measure the lengths of the top and
bottom ramps. This is illustrated in Figure 12. Record
these lengths. They are the only measurements
required for this test.

41. Slice Thickness
How the Measurements Are Analyzed
 The slice thickness is calculated using the following
formula:
 slice thickness = 0.2 x (top x bottom)/(top +
bottom)
 where top and bottom are the measured lengths of
the top and bottom signal ramps. For example, if
the top signal ramp were 59.5 mm long and the
bottom ramp were 47.2 mm long, then the
calculated slice thickness would be
 slice thickness = 0.2 x (59.5 x 47.2)/(59.5 + 47.2)
= 5.26 mm.

42. Slice Thickness
Recommended Action Criteria
 For both ACR series the measured slice thickness
should be 5.0 mm ± 0.7 mm. Errors greater than
+/-1.0 mm fail.

43. SLICE POSITION ACCURACY
 The slice position accuracy test assesses the accuracy with which slices can be
prescribed at specific locations utilizing the localizer image for positional
reference.
 A failure of this test means that the actual locations of acquired slices differ
from their prescribed locations by substantially more than is normal for a well-
functioning scanner.

44. SLICE POSITION ACCURACY
What Measurements Are Made
 Measurements are made for slices 1 and 11 of the ACR T1 and ACR T2 series.
 1 Display the slice. Magnify the image by a factor of 2 to 4, keeping the vertical bars of the
crossed wedges within the displayed portion of the magnified image.
 2 Adjust the display window so the ends of the vertical bars are well
 3 Use the on-screen length measurement tool to measure the difference in length between the
left and right bars. The length to measure is indicated by the arrows in Figure 14.

45. SLICE POSITION ACCURACY

46. SLICE POSITION ACCURACY

47. SLICE POSITION ACCURACY
Recommended Action Criteria
 The absolute bar length difference should be 5 mm or less, but up to 7 mm is acceptable.
 A bar length difference of more than 4 mm for slice 11 will adversely affect the low-
contrast object detectability score. So, although 5 mm is acceptable for this test, it is
advisable to keep the bar length difference to 4 mm or less.

48. Geometric Accuracy
 To verify that the image is scaled in a manner reflecting the true dimensions of the
body part under investigation.
 Phantom: ACR phantom
 Measurement:
 Use the scanner’s distance-measuring function to determine the diameter of the signal-
producing circular phantom, measured vertically through the center of the phantom.
 Use the scanner’s distance-measuring function to determine the diameter of the signal-
producing circular phantom, measured horizontally across the center of the phantom.
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49. Geometric Accuracy
 Geometric accuracy measurements on
the ACR MRI accreditation phantom,
when measured over a 25-cm field-of-
view for the large phantom and a 10-
cm field of view for the small phantom
are generally considered acceptable if
they are within ±2 mm of the true
values.
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50. Visual checklist
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51. If QC Test Fails
 Common errors-
 Check for magnetic objects in bore
 Re-seat head coil
 Reposition & landmark phantom
 Make sure scan room door securely closed
 Repeat daily QC scan procedures
 Record results again in QC datasheet

52. Weekly QC data sheet
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53. Action criteria from ACR and AAPM
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54. References
 Quality Control manual for MRI, ACR, 2015
 Quality assurance methods and phantoms for magnetic resonance imaging: Report of
AAPM nuclear magnetic resonance Task Group No. 1, Medical Physics, Vol. 17, No. 2,
Mar/Apr 1990.
 Acceptance Testing and Quality Assurance Procedures for Magnetic Resonance Imaging
Facilities, Report of MR Subcommittee Task Group I, December 2010.
 Concepts of Quality Assurance and Phantom Design for NMR Systems, Medical Physics
Monograph No. 14, NMR in Medicine: The Instrumentation and Clinical Application,
edited by S.R. Thomas and R.L. Dixon, (American Institute of Physics, NY, 1985).

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