• Topic ID: id_12374689
  • Version: 1.6
  • Date: Jul 5, 2019 6:08:29 PM

Test T/R Pin Diode for Noise (Head or Body)

Prerequisites

Table 1 Personnel requirements
Required persons Preliminary requirements Procedure Finalization
1 Not Applicable 15 minutes 20 minutes

Overview

The Pin Diode Test identifies if the T/R Diode is creating excess noise. It takes two noise scans with and without T/R enabled. This procedure will not assist in diagnosing T/R faults.

Procedure

  1. Start a new study.
  2. Select either the Head or Body Coil.
    1. If testing the head coil, place it on the cradle, landmark on the coil, and advance to scan.
    2. If testing the body coil, landmark on a valid cradle position and advance to scan. Do not install or use a phantom.
  3. Set up to scan using the following protocol:
    1. Axial
    2. 2D
    3. GRE
    4. TE: 34 (OK to use a different value to please scanner)
    5. TR: 20 (OK to use a different value to please scanner)
    6. Flip angle: 10 (OK to use a different value to please scanner)
    7. Bandwidth: 15.63 (15 to16 KHz OK)
    8. FOV: 24
    9. Slice thickness: 10 mm
    10. Space: 1.5 mm (OK to use a different value to please scanner)
    11. Start: 0
    12. Stop: 0
    13. Yres: 256
    14. Xres: 256
    15. NEX: 1
  4. Download series.
  5. Click arrow next to the SCAN option, select Research, then Display CVs.
  6. Modify CV “rawmode”, setting the value to 1, then select Accept.
  7. Click the arrow next to Scan button and select Research Options and select Download.
  8. Disable Exciter RF Output by moving the RF ENB switch to the down position. See Figure 1.

    Figure 1. Exciter RF ENB Switch

  9. note:

    The RF ENB switch on the Exciter RF has to be up to Enable RF Output and pushed down to Disable RF Output.

    Enter manual prescan and set R1 and R2 to max, and TG to 0, then exit manual prescan.
  10. Scan and record Study/Series/Image numbers in A column. See Table 2.
  11. Remove TR input going to RF power amplifier.
    1. Remove J3 on RF Amplifier for Head mode.
    2. Remove J2 on RF Amplifier for Body mode.
    3. Remove J13 RF In cable from RF amplifier.

      Figure 2. J2 and J3 on SRFD Amplifier

  12. Turn the TR fault detection switch, on the driver module, to the disable position (down).
  13. Scan and record Study/Series/Image numbers in the B column. See Table 2.
  14. Display the first image from Step 10 and verify there is no coherent noise seen (patterns such as solid or dashed lines, or pattern of dots). Record if coherent noise exists in the A column. See Table 2.
  15. Place an ROI (Region Of Interest) centered on the image and covers 60 to 80 percent of the image.
  16. Record the mean and standard deviation in the A column. See Table 2.
  17. Display the first image from Step 13 and verify there is no coherent noise seen (patterns such as solid or dashed lines, or pattern of dots). Record if coherent noise exists in the B column. See Table 2.
  18. Place an ROI (Region Of Interest) centered on the image and covers 60 to 80 percent of the image.
  19. Record the mean and standard deviation in the B column. See Table 2.
    Table 2 Data Entry and Analysis
    A B
    Study
    Series
    Image
    Mean
    Standard Deviation (STD)
    Coherent noise exists? Yes/No
  20. Analyze the results from Table 2:

    • If coherent noise exists, then the Pin Diode Test is invalid, and this indicates a problem. See Table 3 for potential coherent noise issues.

    • If coherent noise does not exist, perform the following calculation: C=100*(STD_A-STD_B)/STD_A

    • If C is less than ±1.5%, Pin Diodes may be faulty.

    Table 3 Potential Causes of Defective Pin Diodes
    Possible Causes
    Coherent Noise only on A Noise from TR driver getting through bias T in RF power amplifier
    Coherent Noise only on B TR diodes turning on/off by noise
    Coherent Noise on both Noise received from coil from noise in magnet room, or generated by the coil or TR electronics

Finalization

  1. Reconnect any cables that you removed during this procedure.
  2. Place Driver Module TR fault detection switch in Enabled (up) position.
  3. Place RF ENB Switch on Exciter in Enabled (up) position.