L.., ------------
t,J~Jre9J!n l~
Tho Prem/or MRI Registry
Study Group
2010
Hardware - QA/QC
The location of the coils installed in the MRI scanner, from the inner point closest
to the patient to the outer most edge, are: RF radiofrequency coils, gradient coils,
shim coils, main magnet
..)
Gradient Coils
Gradient amplitude is defined as the strength of the gradient.
The gradient rise time is defined as the time it takes for the gradient to reach its
full amplitude, measured in microseconds --- mT/m (milliTesla/meter) or G/cm
(Gauss/centimeter). Equally synonymous as the units of gradient strength
measurement -- 10 mT/m = lG/cm
V
Plateau / Peak Gradient Strength
I Trapezoidal
I gradient pulse
' utilized in
Gradient conventional pulse
Amplitude f sequences
..... .....
Time
Rise Fall
T·me Time
The i@dient slew rate]is the ~peed:rate1of ai ce @ or descent of a gradient from
~ero to its maxirfiu m amplitud_g, either positive or negative. Which is the amplitude
divided by the rise time in msec. Measured in mT/m/msec or T/m/sec. The shorter
the rise t ime, the faster the gradients and therefore echo spacing. Gradients "'1ith a
shorter echo spacing will have better resolution capabilities and more available
,r
slices per TR period . The strength of the gradient over a specific distance is
a ~ r way to define the slew rate .
To convert vendor spatial gradient map into manufacturer conditions chart:
1 Tesla/meter= 100 Gauss/ cm
J
MSG given : 3.5 T/m
Move decimal two places to the right - 3.5 x 100
3.5 T/m = 350 Gauss/ centimeter (G/cm)
Example II 2: 5.2 T/m = 520 G/cm
,.I
** Important for every MRI technologist to know Gauss/ cm for every metallic
implant- manufacturer guidelines/ MRlsafety.com •• varies for each system
/
The duty cycl~i s defined as the t ime th e gradi ents are on during a TR period, the
"gradient working time." Parameter changes affecting the pulse duty cycle
include :
1. Increased II slices
2. Employment of fat suppression pulses (SPAIR requires increased TR
compared to SPIR)
3. Utilization of presaturation slabs/bands
4. Increased ETL
The rapid, successive switching of the gradient coils is the primary cause of the
noise in the MR scan room.
t,J~Jre9J!n l~
Tho Prem/or MRI Registry
Study Group
2010
Hardware - QA/QC
The location of the coils installed in the MRI scanner, from the inner point closest
to the patient to the outer most edge, are: RF radiofrequency coils, gradient coils,
shim coils, main magnet
..)
Gradient Coils
Gradient amplitude is defined as the strength of the gradient.
The gradient rise time is defined as the time it takes for the gradient to reach its
full amplitude, measured in microseconds --- mT/m (milliTesla/meter) or G/cm
(Gauss/centimeter). Equally synonymous as the units of gradient strength
measurement -- 10 mT/m = lG/cm
V
Plateau / Peak Gradient Strength
I Trapezoidal
I gradient pulse
' utilized in
Gradient conventional pulse
Amplitude f sequences
..... .....
Time
Rise Fall
T·me Time
The i@dient slew rate]is the ~peed:rate1of ai ce @ or descent of a gradient from
~ero to its maxirfiu m amplitud_g, either positive or negative. Which is the amplitude
divided by the rise time in msec. Measured in mT/m/msec or T/m/sec. The shorter
the rise t ime, the faster the gradients and therefore echo spacing. Gradients "'1ith a
shorter echo spacing will have better resolution capabilities and more available
,r
slices per TR period . The strength of the gradient over a specific distance is
a ~ r way to define the slew rate .
To convert vendor spatial gradient map into manufacturer conditions chart:
1 Tesla/meter= 100 Gauss/ cm
J
MSG given : 3.5 T/m
Move decimal two places to the right - 3.5 x 100
3.5 T/m = 350 Gauss/ centimeter (G/cm)
Example II 2: 5.2 T/m = 520 G/cm
,.I
** Important for every MRI technologist to know Gauss/ cm for every metallic
implant- manufacturer guidelines/ MRlsafety.com •• varies for each system
/
The duty cycl~i s defined as the t ime th e gradi ents are on during a TR period, the
"gradient working time." Parameter changes affecting the pulse duty cycle
include :
1. Increased II slices
2. Employment of fat suppression pulses (SPAIR requires increased TR
compared to SPIR)
3. Utilization of presaturation slabs/bands
4. Increased ETL
The rapid, successive switching of the gradient coils is the primary cause of the
noise in the MR scan room.
