Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Uterine manipulation is integral to obtaining adequate access to the uterus
during a laparoscopic procedure. A variety of mechanical manipulators have
been developed to aid the surgeon with the dissection of the uterus during
laparoscopic hysterectomies. Limitations of existing manipulators are that
they require an additional assistant during surgery, are expensive and may
cause tissue trauma to the vaginal or cervical canal. This study introduces the
novel concept of a magnetic uterine manipulator, intended to overcome existing
devices’ shortcomings and enabling non-invasive uterine manipulation.
The first goal of the study was to investigate the strengths and weaknesses of
existing mechanical manipulators and compare them to those of a magnetic
device. Analysis showed that a magnetic manipulator would not be able to
compete in terms of the range of motion of existing devices. A limited anteriorsagittal
rotation range of 60 was seen in the magnetic manipulator compared
to a range of 140 in mechanical devices. However, the magnetic manipulator
could eliminate the need for an extra assistant, is reusable and thus also more
economical. The second goal was to investigate which type of setup would be
most successful at effective uterine manipulation. Through concept analysis a
cart-on-arch system was deemed most effective. To lift an effective load of 1
N over an air-gap of 150 mm rare-earth N38 Neodymium (NdFeBr) magnets
showed the most promise as magnetic actuators. FEA (Finite Element Analysis)
simulations of the magnetic setup were validated experimentally which
produced an acceptable MAE (mean absolute error) of 0.15 N. Furthermore,
a comparative simulation study of shielded and unshielded magnets was done
which concluded that shielded magnets produce a slightly higher attraction
force and would be safer to use due to less magnetic flux fringing. Thirdly and
lastly, potential safety hazards and risks of using magnetic actuators in surgical environments were identified. The literature research revealed that connections
between magnetic fields and health risks to patients have not been conclusively
proven in clinical studies to date, but nonetheless, great care should be taken
in situations where the patient has a pace-maker or orthopaedic implants, as
these might interact with the magnetic field. Recommendations for future
work include further research into the geometry and scaling effects of magnetic
shielding as well as electromagnetic actuator design. Electromagnetic
actuators could replace rare-earth magnets, if coil and cooling systems are optimized,
resulting in magnets that can be reversed or switched off and which
are therefore easier to control and safer to handle. / AFRIKAANSE OPSOMMING: Ontwikkeling van ’n Magnetiese Intra-Uteriene Manipuleerder
Baarmoedermanipulasie is van uiterste belang om sodoende voldoende toegang
te kry tot die baarmoeder gedurende ’n laparoskopiese prosedure. Daar
is reeds ’n verskeidenheid meganiese manipuleerders ontwikkel as hulpmiddel
vir die chirurg in die ontleding van die uterus tydens laparoskopiese histerektomies.
Beperkings van bestaande manipuleerders is dat ’n bykomende assistent
tydens chirurgie benodig word. Die manipuleerders is ook duur en kan weefseltrauma
veroorsaak aan die vaginale of servikale kanale. Die studie stel ’n nuwe
konsep bekend: ’n magnetiese baarmoedermanipuleerder, gemik daarop om
bestaande toestelle se tekortkominge te oorkom en nie-indringende baarmoedermanipulasie
moontlik te maak. Die eerste doel van die studie was om die
voordele en nadele van bestaande meganiese manipuleerders te ondersoek en
dit te vergelyk met dié van die magnetiese toestel. Analise het getoon dat
’n magnetiese manipuleerder nie met bestaande toestelle sal kan kompeteer
waar dit gaan om beweegruimte nie. Daar is ’n beperkte anterior-sagitale rotasiespeling
van 60 in die magnetiese manipuleerder, terwyl die meganiese
toestel ’n rotasiespeling van 140 het. Die magnetiese manipuleerder kan egter
die nodigheid van ’n bykomende assistant uitskakel, is herbruikbaar en dus
ook meer ekonomies. Die tweede doel van die studie was om die tipe opstelling
wat meer suksesvol sal wees tydens doeltreffende baarmoeder manipulasie te
ondersoek. Konsep-analise het getoon dat ’n "cart-on-arch"stelsel die beste sal
werk. N38 Neodimium (NdFeBr) magnete het die beste vertoon as magnetiese
aandrywer om ’n werklike belasting van 1 N oor ’n lugspasie van 150 mm te
lig. EEA (Eindige Element Analise) simulasies van die magnetiese opstelling is eksperimenteel bekragtig en het ’n aanvaarbare gemene absolute fout (GAF)
van 0.15 N gelewer. ’n Vergelykende simulasie studie het verder gewys dat
beskutte magnete ’n effens hoër aantrekkingskrag oplewer en sal dus veiliger
wees om te gebruik vanweë die verminderde magnetiese stromingsrand. Derdens
en laastens is potensiële veiligheidsrisikos en gevare in die gebruik van
magnetiese drywers in chirurgiese omgewings geïdentifiseer. Literatuurnavorsing
het onthul dat die verband tussen magneetvelde en gesondheidsrisikos
aan pasiënte nog nie voldoende bewys is in kliniese studies tot op datum nie.
Gevalle waar pasiënte ’n pasaangeër of ortopediese inplantings het moet met
groot sorg hanteer word aangesien dit dalk kan reageer met die magneetvelde.
Aanbevelings vir toekomstige werk sluit verdere navorsing in in die rigting
van die geometrie en die afskilferingseffek van magnetiese beskutting en ook
elektromagnetiese drywer ontwerp. Elektromagnetiese drywers kan moontlik
rou aarde magnete vervang indien winding en afkoelstelsels ge-optimeer word
wat kan lei tot magnete wat omgekeer of afgeskakel kan word en dus makliker
beheerbaar is en veiliger om te hanteer.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/19935 |
| Date | 03 1900 |
| Creators | Doll, Stefan |
| Contributors | Scheffer, C., Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 82 p. : ill. |
| Rights | Stellenbosch University |
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