We present procedures performed with a newly developed echo-navigator (Masmec,
Italy) which enables probe-oriented or needle oriented procedures,
integrating the virtual tracking with fusion imaging (fig.4).
The patient is placed in a prone position on the bed, ready to perform the fusion imaging infiltration.
Step 1 Ultrasound equipment and setting
We used a newly 'ECO-NAV’ fusion imaging system (MASMEC,
Italy), equipped with needle-tip sensors and 3-5 MHz convex probe with integrated electromagnetic position sensors.
The echo-navigator integrates the ultrasound machine with a low-intensity magnetic field generator docked by wire to the ultrasound machine.
MR or CT images are loaded using standard DICOM format on the US machine through CD-ROM device or USB.
The MR protocol used is a volumetric HYCE sequence with TR 10 ms,
TE 5 ms,
ST 1,70 mm,
FOV 220 9 220 mm,
Flip Angle 70°.
ECONav software allowed us to choose the sequences to be merged with the ultrasound image,
before calibration.
For correct superimposition of ultrasound and MR images,
we defined body landmarks with both imaging techniques such as bony contours of: spinous process of the second,
third,
fourth and fifth lumbar vertebra,
posterior superior iliac spine,
first posterior sacral foramen,
and the sacroiliac joint.
Image calibration occurs through two steps.
In the first step,
it is mandatory to find an ultrasound scan consistent with the orientation of the MR or CT; we placed the probe at the level of the spinous process of L5,
upright and with axial orientation.
When the MR/CT scanning plane corresponds to the ultrasound scanning plane and the operator provides the confirmation input,
the software connects the MR/CT image to the ultrasound,
allowing a synchronous motion,
consistent with movements and rotations of the probe.
The second step involves calibrating end of three anatomical landmarks of the two imaging methods.
We have found it convenient to use as landemarks:
- the spinous process of the L5;
- the two facet joints of L5/S1.
Now,
the images are synchronized and image superimposition can be activated check the accuracy of the calibration.
Step 2: fusion imaging injection
We have two procedural modalities:
- probe-oriented procedure: the probe has a biopsy line guide and with a sensor-base needle it's possible to reach the target (facet joints,
sacoiliac joint or foramen) by checking in real time the actual correspondence of MR images with the US images;
- needle-oriented procedure: the sensor-tip needle can be used such as a probe and based on the MR/CT imagines,
we can proceed with the introduction of the needle,
reaching the goal.
The procedures are performed with 21G needles,
90 mm in length,
with a solution of 0.5 ml methylprednisolone acetate 40 mg/ml (Depo-medrol,
Pfizer,
Italy),
diluted with mepivacaine hydrochloride 2% 0.5 ml and 5 ml ozone.