Gradient Polarity Checks

Prerequisites

Table 3. Safety

warning

POISON HAZARD!
1.5T and 1.0T Phantoms CONTAINS NICKEL, A SUSPECT CARCINOGEN.
DO NOT INGEST. DISPOSE OF AS A HAZARDOUS WASTE ACCORDING TO STATE AND FEDERAL REGULATIONS.

Reversal of the polarity of a single gradient causes the right/left or top/bottom reversal of the images from two axes, and reversal of the offsets for one axis. Incorrect polarity of all of the gradients causes the images from all planes to be upside down and backward, and causes the system to scan offset images in the opposite direction from those commanded for all axes.

note:

The values mentioned in this procedure are related to the physical x, y, and z gradient amplifiers, respectively. The values for setting x-, y-, and z-gradient to obtain 1 gauss/cm, respectfully, are in the system configuration file.

Procedure

Place the DQA-III phantom and loader in the head coil. Position it with the fill plugs up, and toward rear of magnet (see Figure 1).

Figure 1. DQA PHANTOM POSITIONING
Landmark in the sagittal and axial planes (DQA-III coronal plane is not at isocenter).
At front enclosure on scanner, press LANDMARK, then MOVE TO SCAN.

At the Operator Workspace, prepare the system for a “Geometry Verification, Coronal” scan using the scan protocol found in

Table 4. Coronal Scan Protocol
SCAN OPTION	INPUT
Patient Register	New Pt
PATIENT INFORMATION
Patient ID	geservice
Patient Name	gradient polarity
Weight (LB)	111
	Landmark
Landmark	[>]Nasion
PATIENT PROTOCOLS
Patient Position	[>]Supine
Patient Entry	[>]Head First
Coil	[>]Head Accept
IMAGING PARAMETERS
Plane	[>]Coronal
Mode	[>]2D
Pulse Seq	[>]Spin Echo Accept
Imaging Options	none (Default)
PSD Name	none
Protocol	no entry
SCAN TIMING
# of Echoes	1 Default
TE	20
TR	300
Bandwidth	15.63
SCANNING RANGE
FOV	24
Sice Thickness	10
Spacing	1.5
A/P Start	0
A/P End	0
# of Slices	1 Default
S/I	0 Default
R/L	0 Default
Table Delta	0.00 Default
ACQUISITION TIMMING
Freq	256
Phase	256
NEX	1
Phase FOV	`1:00` Default
Freq Dir	[>]S/I
Auto Center Freq	[>]Peak

Move To Lowest Window	Save Series

note: The Exam Description name must be exact because it is used by the automated analysis tool (Daily Quality).

Click on Scan (system auto prescans first).
On the scan desktop, click on Autoview. When the image displays, verify that the CS appears in the upper right-hand corner (see Figure 2).

Figure 2. DQA-III PHANTOM GEOMETRY

note:
Top/bottom reversal is caused by improper z-gradient polarity (wires crossed between output of Gradient Amplifier and input of Gradient Coil). Left/right reversal is caused by improper y-gradient polarity.
At the Operator Workspace, click on New Series.

At the Operator Workspace, prepare the system for a “Geometry Verification, Axial” scan using the scan protocol shown in Table 5

Table 5. Axial scan Protocol
SCAN OPTION	INPUT
Patient Register	New Pt
PATIENT INFORMATION
Patient ID	geservice
Patient Name	gradient polarity
Weight (LB)	111
	Landmark
Landmark	[>]Nasion
PATIENT PROTOCOLS
Patient Position	[>]Supine
Patient Entry	[>]Head First
Coil	[>]Head Accept
IMAGING PARAMETERS
Plane	[>]Axial
Mode	[>]2D
Pulse Seq	[>]Spin Echo Accept
Imaging Options	none (Default)
PSD Name	none
Protocol	no entry
SCAN TIMING
# of Echoes	1 Default
TE	20
TR	300
Bandwidth	15.63
SCANNING RANGE
FOV	24
Sice Thickness	10
Spacing	1.5
A/P Start	0
A/P End	0
# of Slices	1 Default
S/I	0 Default
R/L	0 Default
Table Delta	0.00 Default
ACQUISITION TIMMING
Freq	256
Phase	256
NEX	1
Phase FOV	`1:00` Default
Freq Dir	[>]S/I
Auto Center Freq	[>]Peak

Move To Lowest Window	Save Series

note: The Exam Description name must be exact because it is used by the automated analysis tool (Daily Quality).

Click on Scan (system Auto Prescans first).
When the axial image displays, verify that the A appears in the lower-middle of the image. The image should have the GE logo in the upper right-hand corner (see Figure 2).

note:
Left/right reversal is caused by incorrect polarity of the X gradient. Top/bottom reversal is caused by improper Y gradient polarity.
Click on End and select End Exam to exit.

Finalization

Put away any phantoms and any other tools used for the test.