The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
Aalto

Methods for Interventional Magnetic Resonance Imaging

Erkki Vahala

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Electrical and Communications Engineering, for public examination and debate in Auditorium S3 at Helsinki University of Technology (Espoo, Finland) on the 18th of December, 2002, at 12 noon.

Overview in PDF format (ISBN 951-22-6132-4)   [551 KB]
Dissertation is also available in print (ISBN 951-22-6130-8)

Abstract

This thesis has as its central aim to demonstrate, develop, discuss and promote new methods and technology for improving interventional low field magnetic resonance imaging. The work addresses problems related to accurate localization of minimally invasive surgical tools by describing novel devices and improvements to prior art techniques, such as optical tracking. In addition to instrument guidance, ablative treatment of liver tumours is discussed in connection with low field temperature measurement and the work describes suitable sequences for qualitative temperature imaging.

For instrument localization, a method utilising ex vivo Overhauser enhancement of a catheter like structure was demonstrated. An enhancement factor of 10 was achieved, proving that a substantial signal gain is possible through the use of ex vivo-enhanced liquid. Similarly, a method for biopsy needle tip tracking was developed; where the position of the tip was tracked with a signal from a miniaturized electron spin resonance sample and gradient pulses. At an update rate of 10 samples per second, the accuracy was measured to be better than ±2 mm within a homogeneous sphere of 300 mm.

Optical tracking methods concentrated on new indications of use for the developed optical tracking system and associated software: The system was applied to guide the needle 35 times into first sacral root foramina, with a success rate of 97%. It was also used in five bone biopsies, all of which were performed successfully, the samples allowed for a pathologic diagnosis, and the percutaneous procedures could be performed in less than 40 minutes. A new patient tracker device was developed for staged neurosurgical procedures and demonstrated with two patient cases.

In the temperature measurement study, spin echo, gradient echo and completely balanced steady-state free precession sequences were optimized for maximal temperature sensitivity and the optimized sequences compared. The steady-state sequence seemed the most promising for the prediction of ablated volume in liver.

This thesis consists of an overview and of the following 6 publications:

  1. Vahala E, Ylihautala M, Ehnholm G, Etelä N, Young I, Golman K, Leunbach I. A Study of the Use of Overhauser Enhancement to Assist with Needle and Catheter Placement during Interventional MRI. Journal of Magnetic Resonance 157:298-303 (2002). DOI 10.1006/jmre.2002.2595. © 2002 Elsevier Science. By permission.
  2. Ehnholm G, Vahala E, Kinnunen J, Nieminen J, Standertskjöld-Nordenstam CGM, Uusitalo M. Electron Spin Resonance (ESR) Probe for Interventional MRI Instrument Localization. Journal of Magnetic Resonance Imaging 10:216-219 (1999). © 1999 Wiley. By permission.
  3. Ojala R, Vahala E, Karppinen J, Klemola R, Blanco Sequeiros R, Vaara T, Tervonen O. Nerve Root Infiltration of the First Sacral Root With MRI Guidance. Journal of Magnetic Resonance Imaging 12:556-561 (2000). © 2000 Wiley. By permission.
  4. Ojala R, Blanco Sequeiros R, Klemola R, Vahala E, Jyrkinen L, Tervonen O. MR-Guided Bone Biopsy: Preliminary Report of a New Guiding Method. Journal of Magnetic Resonance Imaging 15:82-86 (2002). © 2002 Wiley. By permission.
  5. Vahala E, Ylihautala M, Tuominen J, Schiffbauer H, Katisko J, Yrjänä S, Vaara T, Ehnholm G, Koivukangas J. Registration in Interventional Procedures With Optical Navigator. Journal of Magnetic Resonance Imaging 13:93-98 (2001). © 2001 Wiley. By permission.
  6. Germain D, Vahala E, Ehnholm G, Vaara T, Ylihautala M, Savart M, Laurent A, Tanttu J, Saint-Jalmes H. MR Temperature Measurement in Liver Tissue at 0.23 T With a Steady-State Free Precession Sequence. Magnetic Resonance in Medicine 47:940-947 (2002). DOI 10.1002/mrm.10147. © 2002 Wiley. By permission.

Keywords: interventional MRI, Overhauser, electron spin resonance, optical tracking, thermal ablation

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© 2002 Helsinki University of Technology

Last update 2011-05-26