Spencer Chambers & Nav Sandhu Structures of Biomedical ...€¦ · Spencer Chambers & Nav...

Spencer Chambers & Nav Sandhu Structures of Biomedical Materials 3BA3 2011-2012 1

Medical Imaging Techniques

Image Guided Surgery Application of IGS Future

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X-Rays Fluoroscopy Computed

Topography (CT) Magnetic

Resonance Imaging (MRI)

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Electrodes accelerate towards the cathode, where atomic interactions occur to create 2 types of photons

99% of electron interactions result in no use, only heat is produced

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Much more fun to say than other interaction types

Incident electrons interact with the nucleus of the anode atom (Coulomb's law)

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Occur as the result of electron-electron interactions between incident electrons and those of the anode

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Orbital Carbon (Z=6)

Barium (Z = 56)

Tungsten ( Z=74)

K 0.3 37 69 L 0.1 6 12 M 1.3 2.8 N 0.3 0.6 O 0.04 0.08

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In general, photons above 20keV are desired for an X-ray beam

Energies lower wont penetrate the skin, and may result in undesirable radiation effects

Lower energies are filtered using “Half-Value layers “

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Half-Value Layer For Various Sources (mm)

Source Concrete Steel Lead Tungsten Uranium

Iridium 192

44.5 12.7 4.8 3.3 2.8

Cobalt 60

60.5 21.6 12.5 7.9 6.9

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Collimator

Patient

Casette

Scattering

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An imaging technique to visualize organs during motion

Uses x-rays, and is essentially a “live x-ray video”

Helpful with barium x-rays and cardiac catheterization

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Barium x-rays primarily used for diagnosing abnormalities of the GI tract

Barium sulfate is a metallic chemical that x-rays cannot pass through

Cardiac catheterization allows physician to see the flow of blood to detect arterial blockage

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X-raying a patient and using geometry to construct a “3D” image

Uses Radon Transform to compute geometry

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The human body is largely composed of water and fat, more specifically 63% hydrogen atoms

Protons, electrons, and neutrons possess a fundamental property called magnetic spin

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Without an applied magnetic field, the atoms are all rotating at random

When a magnetic field is applied, the hydrogen atoms align themselves parallel or anti-parallel to the main magnetic field

A 90 degree RF pulse is applied, causing them to orient into xy-plane from z-axis (in direction of magnetic field)

A 180 degree pulse is then applied to get them to dephase

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Signal is collected as protons relax back to the z-axis

T1(spin lattice relaxation time) is the time to reduce the difference between longitudinal magnetization along the z-axis, and the equilibrium value by a factor of e.

T2 (spin-spin relaxation time) is the time to reduce the transverse magnetization by a factor of e

Relaxations occur simultaneously and amount of time you wait to collect signal determines the image you get

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MRI able to determine soft tissue, while CT is better for bones

MRI can image in any plane, including axial, sagittal and coronal

CT can only do axial No ionizing radiation,

such as x-rays, is used

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Image-guided surgery(IGS) a general term used for any procedure in which a surgeon employs tools that can be tracked using various imaging techniques

This type of technology is used to allow for safer surgery with less invasive techniques

IGS employs the use of numerous imaging techniques, for the purpose of this presentation X-Rays, CT scans and MRI imaging will be the focus

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Optical Tracking Electromagnetic

Tracking Tracking Accuracy

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2 Main Approaches :

Optical

Electromagnetic

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Active Tracking ◦ Markers on tool emit infrared signal which is picked up by

sensor which calculates position and orientation of tool

Passive Tracking ◦ Tool has retro-reflective markers adhered to it that reflect

infrared light back to sensor which calculates position and orientation of tool

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Coils are placed within a variable magnetic field. Depending on proximity and orientation relative to this field there is an induced voltage within these sensing coils

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Spinal IGS ◦ CT ◦ C-arm Fluoroscopy ◦ 3D C-arm

Fluoroscopy Sinus IGS ◦ CT Based ◦ Intraoperative MRI

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Prior to surgery, a CT scan of relevant spinal levels is obtained

Data is transferred to computer workstation and reconstructed in 3D

Spine surgically exposed and DRA attached to vertebra

Registration of operative anatomy and image anatomy through “Paired Point Registration”

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A Spinal image-guidance system consists of Electro-optical camera array Surgical reference system (DRA) Customized spinal instruments

LEDs attached to DRA and instruments, and tracked by electro-optical camera array

Optical tracking digitizer directs camera firing and capture of LEDs, and measures 3D position of LEDs

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C-arm fluoroscopy is combined with computer-aided surgical technology to enhance advantages and minimize disadvantages

Fluoroscopic images taken while surgeons stand away from operative field to significantly reduce radiation exposure

The system saves the multiple projections and is moved away from operative field once done

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Drawbacks C-arm

fluoroscopy only able to provide a single planar anatomical position at one time

Occupational radiation exposure still present unlike in CT

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Isocentric C-arm is able to rotate around patient while maintaining spinal anatomy in centre

Can effectively function as a CT scanner Advantages

Image acquisition takes around 2 min No more navigation inaccuracy between

preoperative CT data and intraoperative position

Anatomical registration not necessary No need for preoperative CT scan Postoperative scan can be performed to

ensure accuracy

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Best suited for 3D intraoperative imaging of bones and joints of extremities, entire spine, hip, and maxillofacial applications

Requires only 30-60 seconds for a complete scan

Can combine preoperative CT or MRI images with intraoperative 3D data

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Although it is a low risk surgery, proximity to important structures as well as anatomical anomalies may lead to complications:

◦ Bleeding ◦ CSF Leak ◦ Loss of Vision

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Treatment Sinusitis Removal of Pituitary Tumor Septoplasty (Fixing Nasal Septum) Inferior turbinate submucosal resection

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Intraoperative Fluoroscopy is more effective for bones

Preoperative MRI and CT scans can be different from the intraoperative anatomy

“Brain Shift” Intraoperative MRI helps with soft tissue surgery

such as brain tumour removal

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Prior to undergoing surgery, a patient undergoes a CT/MRI scan which produces a series of images of the effected area

These images are then converted to 3D images showing all relevant details

This 3D map is then synchronized with real time information inputted from cameras within the operating room

If desired, these views are also coupled with an endoscopic camera and displayed on a screen

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Robotic Surgery ◦ Da Vinci Surgical

System

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Robotic Surgery eliminates need for some personnel in a surgery

Doctor operates on patient from a computer console

Telesurgery possible Major drawback is latency

Minimally invasive with less pain, trauma, and bleeding Leads to faster recovery

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http://www.intuitivesurgical.com/products/davinci_surgical_system/overview_video.html

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http://www.entsurgicalillinois.com/services-sinus-surgery-ent-surgical-consultants-otolaryngology-joliet-in.html#septoplasty

[8] V.P.Escabasse, A.Coste.(2010).”Image Guided Sinus Surgery” [Online]. Available : http://www.sciencedirect.com. [9] P.Sprawls.(2000). The Physical Principles of Medical Imaging.(2nd Edition).[Online]. Available:

http://www.sprawls.org/ppmi2/ [10]Binding Energies.(2005) “XPS Spectra”. [Online]. Available :

http://www.casaxps.com/help_manual/manual_updates/xps_spectra.pdf [11] Chris Budd.(2010). “Saving lives: the mathematics of tomography”.[Online]. Available

http://plus.maths.org/content/os/issue47/features/budd/index [12] Non-Destructive Testing Resource Center.(2011). “X-Radiation”.[Online]. Available: http://www.ndt-ed.org/EducationResources/CommunityCollege/Radiography/Physics/xrays.htm [13]T.M.Peters.(2001)”Image Guided Surgery and Therapy: Current Status and Future Directions” University of Western Ontario.

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[14] ARCADIS Orbic 3D. (n.d.). Siemens Healthcare worldwide. Retrieved November 20, 2011, fromhttp://www.medical.siemens.com/webapp/wcs/stores/servlet/ ProductDisplay?storeId=10001&langId=-1&catalogId=1&productId=143790-catTree=0100010,14264

[15] Da Vinci Surgical System. (n.d.). da Vinci Surgery . Retrieved November 20, 2011, from http://www.davincisurgery.com/davinci-surgery/davinci-surgical-system

[16] Fluoroscopy. (2006, June 2). Radiology. Retrieved November 10, 2011, from www.umm.edu/radiology/fluroscopy

[17] Foley, K. T. (1996). Image-Guided Spinal Surgery. Neurosurgery Clinics of North America, 7(2), 64-68. [18]Holly, L. T. (2006). Image-Guided Spinal Surgery. The International Journal of Medical Robotics and

Image Guided Surgery, 2, 7-15. [19] NeuroLove: How does MRI work? . (2010, December 7). NeuroLove. Retrieved November 10, 2011,

from http://neurolove.tumblr.com/post/806853019/how-does-mri-work-the-best-explanation-for-how

[20]Time constants T1 and T2. (n.d.). MRI physics. Retrieved November 10, 2011, from http://www.revisemri.com/questions/basicphysics/time_constants

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