Jan’s Blog

Autoren:

• National Center for 3D Ultrasound in Surgery, Trondheim, Norway
• NTNU – Norwegian Technoloy of Science and Technologie
• SINTEF – Largest independent Research Organisation in Scandinavia

Inhalt:

They described a solution for the integration of intraoperative laparoscopic ultrasound (2D / 3D) navigation technology for guidance of laparoscopic procedures.

• Disturbance of OR equipment for EM-Tracking
  •  Increase of the RMS distance error from 0.3mm to 2.3mm in the center of the measurement volume
  • Surgical Instruments / Ultrasound prove added no further  inaccuracies
• Laparoscopic ultrasound (LUS) was first introduced by Fukuda and coworkers in 1982.
  • Advances in CT and MRI technology decreased the attention of diagnostic LUS
• Renewed enthusiams for LUS in the 1990s with the introduction of laparoscopic cholecystectomy as a standard procedure for cholecystolithiasis and more advanced ultrasound technology
• Drawbacks of LUS:
  • For incexperienced clinicians interpretation and orientation of the image in relation to the patient anatomy can be a challenge (limited depth and width perception)
    • Image quality is operator dependent
  • Size of LUS images is small due to a small tranducer array size (foot print of the probe)
  • Disadvantages compared to CT and MRI:
    • lower Signal-to-Noise ratio in some cases
    • the specular nature of the modality cause:
      • shawdoing
      • multiple reflections artefacts
      • variable contrast
• The four common technologie for tracking medical instruments are (Cinquin et al. (1995) Computer assisted medical inventions,IEEE Eng. Med. Biol. Magazine:
  • Electromagnetic (EM)
  • optical
  • mechanical arm
  • acoustic
• References for tracking accuracy/distortion evaluation (EM, optical)
• Calibration in navigation is the transformation, determining the image position and orientation in relation to the sensor.
• Übersicht anTracking Herstellern
  • NDI: www.ndigital.com
  • Atracsys: atracsys.com
  • Claron Technolog: www.clarontech.com
  • Polhemus: www.polhemus.com
  • Ascencion Technology: www.ascencion-tech.com
• Advantages Ultrasound:
  • inexpensive
  • compact
  • mobile
  • no requirements for special facilities for use in the OR
  • image quality has improved in recent years
  • US contrast agents and new processing technologies will add new possibilities due to improved image quality and structure detection
  • real-time imaging
• Relevant visualization information should not only include anatomical structures for reference and pathological structures to be targeted (CT/MRI/US tissue), but also important structures to be avoided, like blood vessels (CT/MR constrast, ultrasound doppler)
• Overlay of CT + US is computational intensive, but becomes more and more feasible through the employment of GPUs
• Another challenge is shifting anatomy due to surgical manipulations. The most important approach to solve this problem is direct navigation surgery based on intraoperative ultrasound imaging. Another approach is also to correct preoperative data by using intraoperative ultrasound by shifting or morphing of preoperative images.
• Most important factor for influencing the accuracy, besides movement of organs, may be the nature of the tracking system and the ultrasound calibration
• Largest distortion for EM tracking in their setup was the OR table
• For high precision tasks their accuracy was not high enough and only endoscopy and real-time 2D US may be accurate enough
• Probe calibration is perhaps the largest source of error in 3D freehand ultrasound acquisitons
• The overall clinical accuracy in imag-guided surgery is the difference between where a surgical tool is located relative to some structure as indicated in the image information presented to the surgeon, and where the tool is actually located relative to the same structure in the patient
• Registration accuracy prior to surgery adds even more inaccuracy
• Multimodal imaging can help to compensate possible anatomy shifts

Sprache:

Introduction:

• Laparoscopic surgery is performed through small incisions that limit free sight and possibilty to palpate organs. Although endoscopes provide an overview of organs inside the body, information beyond the surface of the organs is missing. Ultrasound can provide real-time essential information of inside organs, which is valuable for increased safety and accuracy in guidance of procedures.
• Compared to open surgery, laparoscopic surgery presents the surgeon with a set of challenges. One of these is the restircted view inside the body cavity through the video laparoscope. Another limitation is the inability to palpate through the rigid laparoscopic instruments. Ultrasound can compensate for some of these limitations intraoperatively by allowing the surgeon to see into tissue, i.e. beyond the surface of the organs. Furthermore, ultrasound can visualize blood vessels, important for avoiding bleeding, and its real-time capabilites provide the surgeons with immediate feedback of changes that occur. The image quality of ultrasound systems has also increased in recent years and the equipment is cheaper and more portable than alternative intraoperative imaging modalities such as CT and MRI.
• Specular nature of the modality = Information is gathered through reflections

Journal: IPF 1,611