QUALITY ASSURANCE IN MRI TO MAINTAIN THE EFFICIENCY OF MRI MACHINE AND OPTIMUM IMAGE QUALITY

Quality control plays a pivot role to maintain optimum image quality as well as to increase life of the imaging modality. Hence there is a need to do quality control check ups periodically.

1. MRI QC

2. CONTENT

* ARRT Requirement
* General MRI QC Check
* MRI QC Phantom
* Daily/Weekly MRI QC
- Setup & Table Position Accuracy
- Central Frequency
- Transmitter Gain
- Geometric Accuracy
- High-Contrast Spatial Resolution
- Low-Contrast Detectability
- Artifact Evaluation
* Annually MRI QC
* MRI QC Form

3. ARRT Requirement

MAGNETIC RESONANCE IMAGINO ARRT BOARD APPROVED: JANUARY 2019
DIDACTIC ANO CLINICAL COMPETENCY REQUIREMENTS IMPLEMENTATIONDATE: JANUARY 4, 2020

4,24 MRI Quality Control Procodures

Candidates must demonstrate competence in the seven quality control activities listed below.
The first four procedures are performed on a QC phantom.

MRI Quality Control Proceduros

[_ Signal to Noise Ratio

[_ Center Frequency
Transmitter Gain or Attenuation

Equipment Inspection
(eg. Colts, Cables. Door Seats)

Monitor Cryogen Levels

Room Temperature and Humidity

4. GENERAL MRI QC CHECK

5. General MRI QC Check

* Instrument inspections:
(1) Coil
(2) Cables
(3) Door seals
(4) Room temperature
(5) Room humidity
(6) Contrast media injector
(7) Communication tool
(8) Headphone or earplug
(9) Monitor eryogen levels
{10} Ferromagnetic detector

* Visually observation,

* Record when there is defect or any malfunction

6. à
Knowing that many MRI coil failures are
related to the cable

7. MRI Artifacts: Zipper

RF shield at the MRI door. Prevent any external RF entering the scanning room from electronic
devices. Preventing from Zipper artifact.

8. MRI Room Control

Temperature

& Humidity

%

The MRI scan was
performed at room
temperature (20°C-22°C)
with a relative humidity of
35%-40%.

9. Make sure
the contrast
media
injector ina
good
condition.

10. Two-ways intercom
system

11. =

e
Y

Headphone must be
operated well, can hear the
radiographer instructions €

prevent from loud sound
produce by MRI machine.

12. Monitor cryogen levels

* Cryogen = a substance used to produce

Helium fill and cold head
very low temperatures.

* In MRI, cryogen = Helium liquid Outer cold shield
‚Helium vessol
* The main magnet windings are bathed in
liquid helium (4°K or -269°C) in a
structure called a cryostat. The cryostat is
a multi-compartmental structure that
functions like a Thermos bottle.

* Percentage of liquid Helium used by MRI
machine varies. Siemens MRI machine
used up to 3 — 6% per month. Philips
Achieva used 1% per month.

13. Monitor cryogen levels

What to Keep in Mind Regarding Helium Refill in MRI
Machines?

Must > 65% of Helium liquid in the MRI system.

14. Ferromagnetic
Detector

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15. MRI QC PHANTOM

16. MRI QC Phantom

17. Filling with solution of nickel chloride and sodium
chloride. In about 7.26 Kg weight.

MRI ACR Phantom DM

190 mm

N
sr E

‘Marked with retorence points for nose and chin. The Phantom is approved by the American Collage of Radiology and ts compatible withthe ACR Phantom
Cradle listos below (sold separate)

18. NC.

Positioning & Set-up of the ACR MRI Phantom

19. https; y Pv=kil NY

20. 1 sagittal slices & 11 axial
slices of MRI images can
be produced from the
ACR MRI phantom to
perform different QC
tests.

21. DAILY/WEEKLY MRI QC

22. Daily/Weekly & Annually MRI QC
DAILY/WEEKLY

* Setup & Table Position Accuracy
* Central Frequency

* Transmitter Gain

* Geometric Accuracy

* High-Contrast Spatial Resolution
* Low-Contrast Detectability

» Artifact Evaluation

23. Setup & Table Position Accuracy

* Measure in mm unit.
* Button/Console
* Laser

* Accuracy or table movement &
position in mm.

*+5mm

24. Central Frequency (CF)

* Measure in Hz unit.

* Measure the frequency of the hydrogen
in the water during MRI.

* Based on Larmour frequency formula,
W = YB (y = gyromagnetic ratio (42.58 MHz/T) & B = MRI
machine magnet strength (T))

» CF for 1.5 T should be = 63.87 MHz,
whereas CF for 3.0 T = 127.74 MHz

* Optimum CF for 1.5 T = 63870000 Hz. ==
+ + 100 Hz standard deviation

baseline [63630042
allowable variation (+) [100]

25. Transmitter Gain (Tx)

* Measure in Hz or dB unit.
* Also called as attenuation.

* Measure the radio-frequency power
required to achieve certain flip
angle.

* Depend on RF coils.
* +27 Hz

mean

standard deviation

baseline
allowable variation (+/-)

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26. Geometric Accuracy

* Measure in mm unit.

* Measure the size of diameter
(190 mm) and length (148
mm) ACR phantom on MRI
images and compare it with
real physical ACR phantom
size

* This QC measurement is
important to make sure the
MRI accuracy in measuring

the tumor or abnormality size.

*+2mm

27. High-Contrast Spatial Resolution

+ Measure the ability to detect small
structures (holes).

+ On the ACR phantom, it will
evaluate the separation of holes rape ia
arrange in 2 squares at the upper eu
left (UL) and lower right (LR).

+ 3 sets (1.1 mm, 1.0 mm, 0.9 mm)

+ ropeat for LR array (columns)

* Performance standard = 1.0 mm.

“iimm 10mm 09mm

28. Low-Contrast Detectability

* Count or number of spokes (round structure).

* Measure the ability to differentiate objects with subtle difference in
signal intensity.

* On the ACR phantom, the spokes (round structure) will be count.

* +3 spokes

29. Artifact Evaluation

Check the:

* Distortion

* Ghost artifact in phantom
+ Bright or dark spot

* Inappropriate blurring

30. ANNUALLY MRI QC

31. Annually MRI QC
ANNUALLY

* Magnetic Field Homogeneity
+ Slice Thickness Accuracy

* Radiofrequency Coil Checks
* Monitor Check

Perform by medical physicist or company engineer

32. MRI QC FORM

33. RI EQUIPMENT QUALITY CONTROL

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34. Check your understanding!

https://www.wisc-online.com/arcade/games/natural-science/life-
science/10133/basic-mri-quality-assurance

https://www.youtube.com/watch?v=TaESXP7pVfs

https://www.youtube.com/watch?v=YnWRcul-9kk