Figure 1.
Top view of the prototype ultrasound probe for use in MRI. Array transducers made of 1-3 piezocomposite materials were embedded in the probe (Kyokutan, Japan Probe Co., Yokohama, Japan). The specifications of the array transducers are shown in
Table 1. MR-visible fiducial markers were attached to the probe to locate the probe position and orientation in a three-dimensional MRI image.
Figure 1.
Top view of the prototype ultrasound probe for use in MRI. Array transducers made of 1-3 piezocomposite materials were embedded in the probe (Kyokutan, Japan Probe Co., Yokohama, Japan). The specifications of the array transducers are shown in
Table 1. MR-visible fiducial markers were attached to the probe to locate the probe position and orientation in a three-dimensional MRI image.
Figure 2.
MR-visible fiducial marker. (POM: polyoxymethylene).
Figure 3.
A simultaneous multimodality imaging system consisting of ultrasound (US) imaging equipment (RSYS0006MRF, Microsonic Co., Tokyo, Japan) and an MRI scanner (Echelon Vega, 1.5T, Hitachi Co., Tokyo, Japan). The probe that was placed in the MRI scanner was connected to the US imaging equipment via a connector that passed through the walls shielding the MRI room and the control room.
Figure 3.
A simultaneous multimodality imaging system consisting of ultrasound (US) imaging equipment (RSYS0006MRF, Microsonic Co., Tokyo, Japan) and an MRI scanner (Echelon Vega, 1.5T, Hitachi Co., Tokyo, Japan). The probe that was placed in the MRI scanner was connected to the US imaging equipment via a connector that passed through the walls shielding the MRI room and the control room.
Figure 4.
Composition of the phantom used in the experiment.
Figure 5.
An example of an MRI image of a human crus. The fat layer corresponds to the upper high-brightness region. The sound velocity in fat was measured in the central fat layer. The sound velocity in muscle was measured in the central muscle region between the bottom of the fat layer and the top of the fascia layer (lower-brightness horizontal stripe region).
Figure 5.
An example of an MRI image of a human crus. The fat layer corresponds to the upper high-brightness region. The sound velocity in fat was measured in the central fat layer. The sound velocity in muscle was measured in the central muscle region between the bottom of the fat layer and the top of the fascia layer (lower-brightness horizontal stripe region).
Figure 6.
Cross section of an MRI image corresponding to that of an ultrasound image.
Figure 7.
Comparison of B-mode images of the phantom obtained using the proposed method of compensation (a) and a conventional approach (b). The three red squares indicate ROIs for calculation of the autocorrelation function for a B-mode image.
Figure 8.
Examples of MR images obtained using the simultaneous multimodality imaging system. Each image corresponds to a cross section, and rows of fiducial marker arrays are indicated by arrows. The probe was equipped with two rows of marker arrays, as shown in
Figure 1.
Figure 9.
The estimated cross section of the MR image corresponding to the cross section of the ultrasound image according to coordinates of MR-visible fiducial markers.
Figure 10.
B-mode images of the neck obtained using the proposed method of compensation (a) and a conventional approach (b). A red square indicates a ROI in part of the thyroid for the autocorrelation function in each B-mode image.
Table 1.
Specifications of the array transducers used in MRI.
Bandwidth (MHz) | Number of Elements | Element Pitch (mm) | Element Size (mm) | Focal Length of Acoustic Lens (mm) |
---|
5–8 | 192 | 0.30 | 8.0 × 0.20 | 20 |
Table 2.
Specifications of US imaging equipment.
Maximum Number of Probe Interface Channels | Number of TX/RX Channels | A/D Resolution (Bits) | Sampling Frequency (Hz) | Memory Capacitance Channel (MB) |
---|
256 | 128 | 12 | 31.25 | 256 |
Table 3.
MRI scan parameters for human crus.
Sequence | TR | TE | Thickness | Slices | Frequency Encoding | Phase Encoding |
---|
SE | 937 ms | 19.7 ms | 2.0 mm | 30 | 256 | 180 |
Table 4.
MRI scan parameters for the abdominal phantom and human neck.
Sequence | TR | TE | Thickness | Slices | Frequency Encoding | Phase Encoding |
---|
SE | 1436 ms | 20 ms | 1.5 mm | 45 | 256 | 180 |
Table 5.
The estimated values of sound velocity obtained by simultaneous US imaging and MRI.
| | Subject 1 | Subject 2 | Subject 3 | Average | References [1] |
---|
Fat layer | Length (mm) | 3.58 ± 0.1 | 4.63 ± 0.1 | 4.24 ± 0.1 | - | - |
Time of flight (μs) | 5.02 ± 0.03 | 6.34 ± 0.03 | 5.86 ± 0.03 | - | - |
Sound velocity (m/s) | 1430 ± 40 | 1460 ± 30 | 1450 ± 40 | 1445 ± 20 | 1459–1479 |
Muscle tissue | Length (mm) | 15.00 ± 0.1 | 14.13 ± 0.1 | 15.7 ± 0.1 | - | - |
Time of flight (μs) | 9.75 ± 0.03 | 17.92 ± 0.03 | 20.0 ± 0.03 | - | - |
Sound Velocity (m/s) | 1540 ± 10 | 1580 ± 10 | 1570 ± 10 | 1562 ± 30 | 1540–1566 |
Table 6.
Comparison of the half-widths of the autocorrelation functions in the lateral direction.
ROIs | The Half-Width of the Autocorrelation Function for a Compensated Image | The Half-Width of the Autocorrelation Function for a Conventional Image | Ratio of the Half-Width Improvement |
---|
Left square | 1.35 mm | 2.55 mm | 0.53 |
Center square | 0.85 mm | 2.60 mm | 0.30 |
Right square | 1.33 mm | 3.02 mm | 0.44 |
Average | 1.18 mm | 2.72 mm | 0.43 |