Vertical Bore Imaging

Vertical Bore Imaging




3-Axis Gradient Probes

NB and WB MRI Probes (with gradients and RF)

Our MRI probes are designed for high-field magnets with 40 to 72 mm inside the RT shims. The MRI probe includes the 26-40 gradient coil and 1H or1H/X, rf Litz coils. The probe permits highest gradients at highest fields.

The MRI probe is normally provided with conventional top “NMR-tube” access.

5 mm to 12 mm Imaging Probes

  • Highest S/N
  • 350 G/cm at 2.3% duty cycle, water cooled
  • Quick, convenient, multi-X tuning
  • For magnets up to 900 MHz
  • 5, 8, 10, or 12 mm RF Coils
ASU-Kidney_VB-MRI-A

High resolution images from a healthy rat kidney were acquired at 800 MHz, without contrast (NF), and with contrast (CF). The plot below each image shows the percent change in signal intensity (from mean) versus length, along the yellow line. Each spike on the plot under the contrasted kidney represents a single kidney glomerulus (100-150 µm diameter). Images courtesy of Scott Beeman, Dr. Brian Cherry, Dr. Jeff Yarger, and Dr. Kevin Bennett, Arizona State University.

3-Axis Gradient Coils

comp-3-axis-coils

Partially assembled three-axis gradient coils

3 Axis Gradient Coils

Parameter

Model

26-40

Units

Cooling
method

Water

Diameter
di
for
4%
local deviation

14

mm

Lengthzi for 4%
local deviation

17
mm

Diameter
di
for
10%
local deviation

18
mm

Lengthzi for 10%
local deviation

22

mm

Nearest Gradient
Null point

15.4

mm

Outside
diameter, do

39.6

mm

Coil
half-length, h1

36.1

mm

RF
shield diameter,dS

26

mm

Clear
bore, di

23.6

mm

Max
inductance, L

37

μH

Max
DC resistance, RE

1.4

Ω

Min
gradient gain,
&#945

48

mT/Am

Max
shielding error at
1.5 d0

0.4

%

Min
slew rate, GS =
&#945V/L,
at
1 V

1,189

T/m/s

Continuous
current, IRMS

11

A

Continuous
gradient, GC

53

G/cm

Peak
Voltage

120

V

Approx.
EPI Acoustic Noise, 7 T

70

dBa

Rise
time to GC
for
100 V

4.6

μs

Total
mass

0.4

kg

The performance for the X and Y axis are each as indicated in the table above, however, the Z axis is typically better in slew rate, continuous gradient, and volume of linear region than the above table indicates.

Local deviation (or differential linearity) is defined as the rms deviation from the mean gradient over the specified diameter, di, and length, zi, of the cylindrical sample region. The half-length h1 is the distance from the center to the closer of the two external end surfaces. Eddy currents from the internal RF shield are negligible. The gradient slew rate GS is the instantaneous rate of change in gradient when a 1 V step is applied. The continuous current ratings are true continuous ratings for a single axis with no time limit and adequate cooling. Derate the current 30% when all three axis are driven simultaneously.

Additional Specifications

MRI 3-Axis Gradient Coils

    • Active shielding
    • B0 eddy current compensation
    • Maximum Sample Volume
    • Low Noise and Vibration
    • High Continuous Gradients

Advances in hardware for magnetic resonance imaging (MRI) are needed to improve image quality, ease of use and functionality in high-field MRI research using small objects. Doty’s MRI gradient coils fill this need.

Low-amplitude B0 eddies are induced in the magnet radiation shields primarily from minute variations in coil diameters along the axis or from axial registration errors between the gradient and shield coils. Our use of alumina ceramic for both the gradient and shield formers allows higher precision to be maintained, and low-amplitude eddy current to be minimal. Ceramic coil forms, together with heavy Golay windings dramatically reduce vibration and noise, even at the highest fields. Any remaining B0 eddy is compensated by a time-dependent correction applied to a B0 shim coil. Another advantage of the alumina coil form is its very high thermal conductivity, which helps equilibrate hot spots. The cooling requirements are then satisfied with relatively minor constraints on the winding geometry.

Higher-order eddies are minimized by active shielding. Our coil designs often achieve a factor of 2 better shielding of the transverse gradients than alternative designs.

There is a strong benefit from gradient coil construction with an alumina ceramic coil form and multilayer windings. We significantly reduce acoustic noise, vibration and recovery time compared to gradient coils from other microscopy MR vendors.

Parameter

Model
26-40

Units

Cooling method

Water

Diameter di for 4% local deviation

14

mm

Length zi for 4% local deviation

17
mm

Diameter di for 10% local deviation

18
mm

Length zi for 10% local deviation

22

mm

Nearest Gradient Null point

15.4

mm

Outside diameter, do

39.6

mm

Coil half-length, h1

36.1

mm

RF shield diameter,dS

26

mm

Clear bore, di

23.6

mm

Max inductance, L

37

μH

Max DC resistance, RE

1.4

Ω

Min gradient gain, α

48

mT/Am

Max shielding error at 1.5 d0

0.4

%

Min slew rate, GS = αV/L, at 1 V

1,189

T/m/s

Continuous current, IRMS

11

A

Continuous gradient, GC

53

G/cm

Peak Voltage

120

V

Approx. EPI Acoustic Noise, 7 T

70

dBa

Rise time to Gfor 100 V

4.6

μs

Total mass

0.4

kg

The performance for the X and Y axis are each as indicated in the table above, however, the Z axis is typically better in slew rate, continuous gradient, and volume of linear region than the table indicates.

Local deviation (or differential linearity) is defined as the rms deviation from the mean gradient over the specified diameter, di, and length, zi, of the cylindrical sample region.  The half-length h1 is the distance from the center to the closer of the two external end surfaces.  Eddy currents from the internal RF shield are negligible.  The gradient slew rateGS is the instantaneous rate of change in gradient when a 1 V step is applied.  The continuous current ratings are true continuous ratings for a single axis with no time limit and adequate cooling. Derate the current 30% when all three axis are driven simultaneously.

RF Litz Volume Coils For Vertical Bore NB or WB Probes

RF Coil

I.D.

(mm)

Shield

Diameter

(mm)

Tuning

1H

MHz

Mod. Load

τ 90 ( μs)

Heavy Load

τ 90 ( μs)

1H

31 P

1H

31 P

10

26

1H/X

500

9

12

10

14

12

26

1H

500

9

12

10

26

1H/X

600

11

13

12

15

12

26

1H

800

10

16

For the above coils, the length of homogeneous region is 80% of the coil ID.   Coils with a multi-x channel normally tune 31P through 13C simply by changing plug-in capacitors. All coils feature simple tuning, high B1 homogeneity, external rf shield, and susceptibility matching near the sample region.   

Effectiveness of the litzcage coil:
Effectiveness of the litzcage coil can be seen in the 50 micron resolution of the Mouse brain and Baby Atlantic Sharpnose Shark tail below
.

Mouse brain at 750 MHz, 50-micron resolution

Mouse brain at 750 MHz,
50-micron resolution

Baby Atlantic sharpnose shark, 50-micron resolution

Baby Atlantic sharpnose shark,
50-micron resolution

Both images were taken using a 21 mm CP Litzcage rf coil at 750 MHz inside a Doty vertical bore imaging probe. Images courtesy of Dan Plant, University of Florida, Brain Institute.

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