Medical Physics & Bioengineering

Medical Physics and Bioengineering provides scientific and technical services for safe, effective, and innovative patient care. These services vary from as simple as replacing a specialist battery in a piece of equipment, to as complex as commissioning a new radiation therapy machine. Our patient services range from as close to the patient as administration of radioiodine for thyroid cancer, through to computer simulation of patients.

Medical Physics and Bioengineering is based at Christchurch Hospital. We have three groups on the hospital campus: Radiation Oncology Physics in the Oncology Building, Diagnostic Physics on the 2nd Floor of the Clinical Services Block, and Bioengineering on the Lower Ground Floor of the Riverside Block. Additionally, we provide neurosciences and neurotechnology services as part of the NZ Brain Research Institute just off campus.

You can contact the Medical Physics and Bioengineering Department by
Phone +64 (0)3 364 0531 Fax +64 (0)3 364 0851
email mpbe@cdhb.health.nz

Postal address

Medical Physics and Bioengineering,
Christchurch Hospital,
Private Bag 4710,
Christchurch 8140,
New Zealand.​

Physical address

Medical Physics and Bioengineering – Office,
2nd Floor ​Clinical Services Block,
Christchurch Hospital,
Riccarton Avenue,
Christchurch,
New Zealand.

Sentinel is a patient breathing monitor device we originally made for the Intensive Care Unit (ICU) but is also being used in the Sleep Clinic and Paediatric High Dependency Unit (PHDU).

ICU’s Problem..

Intensive Care Unit specialist Geoff Shaw recognised the need for some sort of alarm while working with patients using CPAP (Continuous Positive Airway Pressure) machines in ICU. With these systems, if the mask becomes loose, isn’t fitting properly, or the connecting airway hose falls off while a patient is asleep, there is no obvious sign of a problem until the patient is distressed.

Geoff noticed that there was a real gap in the market because the ventilator masks which do have alarms are for people who are not spontaneously breathing on their own and cost more than $40,000 each. Geoff saw a need for a low cost device connected to the CPAP machine itself and all the parts, like the mask, that are connected to it.

MPBE Solution…

He got together with Medical Physics & Bioengineering and the Sentinel monitor and alarm device was created. The device uses an electronic pressure sensor, graphical touch-screen display and embedded software, all in a compact box. By working closely with Geoff and the ICU team we tailored the functionality and user interface to their exact requirements. Clinical trials followed in ICU and PHDU with patient and family approval.
The devices and software are made completely in-house using a combination of off-the-shelf components and custom made electrical circuits and mechanical fittings.

Sleep Clinic

Paul Kelly from the Sleep Unit heard about the Sentinel device and immediately found a use with his power-dependent patients who use a non-invasive ventilator in their own homes.

In the event of a power failure, it is not only essential to have a backup power source, but also a smart alarm to notify the caregiver of a critical situation. The Sentinel device helps reduce risk in the event of an emergency. Again, we were able to work closely with Paul to tailor the user interface to meet the different requirements of a home user instead of a clinical user.

One of the most important tasks in Medical Physics is ensuring the quality of treatments delivered to cancer patients undergoing radiotherapy. The main piece of treatment equipment we use for this is a medical electron linear accelerator or “linac”. The linac produces electrons that are traveling close to the speed of light and directs them towards a target that converts them into high energy photons. All of this requires that the beam producing and shaping elements in the linac are aligned with millimetre precision. A linac weighs several tons and rotates about a point in space that is called the “isocentre”. One of the tests we make in ensuring high quality treatment delivery is monitoring how well the linac aligns with its isocentre.
With this in mind we tasked the Bioenginnering workshop with creating a device we can mount on the linac to monitor the alignment with isocentre. The device had to be easy to align as a linac can rotate about two axes and we need to translate about the three orthogonal dimensions of space to determine isocentre. Also, the device had to be able to display deviations from isocentre less than a millimetre.

This required the construction of a rigid, tiltable platform that mounts without slop onto the linac. A pole with a ruler inscribed for determining distance to isocentre is mounted on this platform with micrometer screw gauges controlling the translation. The challenge in making this was accuracy – each and every component of the device had to be made to extremely tight tolerances, provide very precise adjustment and yet be as rigid as possible. By using nitride P20 steel, micrometre barrels celebrated to 0.01 mm, and some precise hand fitting we were able to achieve this. The end result allows us to determine isocentre to within 0.5 mm, which means that treatment delivery is as accurate as possible for our patients.

We were approached by the speech and language therapy community team who were dissatisfied with the commercially available range of assistive devices for drinking. None of these solutions catered for the patient with limited ability to administer, suck and/or swallow fluids and they were reliant on carer contact. Clinicians encountered a range of issues due to these difficulties. Mouth ulcers, urinary tract infections, and dehydration were all compounding the challenge these patients faced with their original condition and affected their quality of life.

Our challenge was to produce a device that addressed this need. The solution we developed in consultation with this clinical team was a powered peristaltic pump with a range of programmable parameters. The bolus size and rate are able to be programmed and additional features such as delivery delay and an audible signal can be set up to suit each user. The benefit of using a peristaltic system is that fluid is only passing through silicone tubing, hence reducing the burden and risks posed by cleaning. The unit is also designed to be compatible with the range of switching and support solutions available to assistive technologists and with which they are already familiar.

The unit is currently being trialled with spinal patients at Burwood Hospital with a view to expanding the trial to other patient groups in the community in the near future.​

The Medical Physics & Bioengineering department was approached by Leeanne Yeoman at the Brain Injury Rehabilitation Service (BIRS) at Burwood Hospital, regarding the design of a low-cost video Frenzel system for diagnosing vestibular dysfunction in their patients.

The basic design of a Frenzel Video system consists of a pair of goggles blacked out to create complete darkness, thereby eliminating visual fixation. A video camera attached to one of the lenses and is illuminated by an infrared light source to enable an image to be displayed and recorded on a computer.

Our solution

Our goggles are specially modified to block out all natural light which is not as easy as it sounds! The camera and infrared light source are magnetically attached and so can be easily moved between left and right eyes.
A second camera in the clinic simultaneously captures the movement of the patient and conversation between the patient and clinician. Both of these videos are recorded together as picture-in-picture so the movement of the eye and movement of the patient are always synchronised. The videos and audio are automatically captured and compressed using open-source software.

This device has been successfully trailed at Burwood Hospital and devices are now being used by BIRS and also by Balance Works Physiotherapy

Staff at the Medical Physics and Bioengineering Department have been working in conjunction with Neurosurgeons from the early 1980s to make titanium plates for reconstructing skulls. We have pioneered some world-leading techniques for designing and making the custom-fitting skull plates. Now we make these plates regularly for the CDHB and other hospitals around New Zealand.

Creating the mould

The process starts with a CT scan and a referral from the Neurosurgeon. Then one of our Imaging Scientists uses special software, written by MPBE, which interpolates the CT scan data to determine the best shape for the implant and ensures the curvature matches that of the surrounding skull. This software then creates a programme for our computer controlled machining centre (CNC Mill) to machine a press mould out of solid epoxy.

Pressing the plate

The implants are made from high-quality Grade 2 titanium sheet, typically 0.5mm thick. The flat plate is then slowly pressed in a custom-built high-pressure hydraulic press up to 3000 psi so that it perfectly matches the shape of the mould.

Creating the 3D model

The CT scan data is also converted to make a 3D model of the skull. This is made either in the CNC mill or using one of our 3D printers. The model allows the neurosurgeon to determine the exact size of the implant. We then use the model to trim the implant to the size drawn by the neurosurgeon.

Finishing the plate

Feathers and screw holes are added to the perimeter of the plate, and drainage and sewing holes are added in positions determined by the neurosurgeon. Once any sharp edges are carefully removed the plate is then chemically polished and then annodised to give a golden colour. This colour makes the plate less visible under the scalp.

In September 2008 the Canterbury Dental Service (CDS) introduced digital radiography for its patients. This replaced conventional radiographs (a wet film taken at the clinic which is then sent to a dark room for processing) which had been used since the 1920s.
The new digital image can be entered into a new electronic oral health record (Titanium) which was also introduced in 2008.
CDS provides oral care for approximately 77,000 Canterbury children. The new digital imaging system is now very much a part of the daily oral health care for these children. Therefore it is essential to ensure that the diagnostic x-ray facilities are providing consistent, high quality images with a minimum of exposure to patients and staff. This is the clinical motivation for quality control checks on equipment, but in New Zealand this is also backed-up with regulatory requirements for all human radiographic imaging to be part of a regular quality assurance programme.
CDHB Clinical Director, School & Community Dental Service Martin Lee and Public Health Dentist Tule Fanakava Misa approached the Medical Physics Bioengineering (MPBE) team for their help in developing systems to test the three components involved in the new digital imaging system. These components are the x-ray generator, plate and scanner, and computer/monitor on which the images are displayed.
Tule teamed up with Nick Cook, MPBE Imaging Scientist to find a solution. He developed a quality assurance programme which monitors performance and function of these components on a regular basis. Central to this new quality assurance programme was a special device, the Quality Assurance Phantom (QA Phantom) that could simulate the demanding aspects of dental x-ray imaging and test the true performance of equipment for clinical imaging. Although the final phantom was simple in design and low cost compared to commercial products, it required precision machining in the MPBE Bioengineering workshop to achieve the required performance.
The phantom consists of a small block of Perspex (PMMA) with a series of different size and depth holes. The Perspex box is placed over an aluminium plate to mimic a tooth with subtle density changes. MPBE also constructed a special protective carry case for the phantoms.
The QA Phantom is located inside a Perspex cylinder that achieves reproducible positioning for repeated x-ray measurements. The x-ray image of the phantom is checked on a calibrated monitor to see how many of the holes are visible and this allows close monitoring of the performance of the machines to correct any problems before they affect patient images.
Each dental clinic and mobile dental facility now has a QA Phantom device so that trained staff can perform monthly checks of the equipment. These checks ensure that the digital dental images are accurate and achieve the performance require to catch any dental problems before they lead to bigger issues. They have been used since beginning of the third school term 2014. Staff have been trained to use the device and do their own checks monthly.
The QA Phantom is used in Christchurch Hospital and community dental clinics but has not been adopted elsewhere in New Zealand as yet because not all dental clinics have switched to digital images.

A partnership between two CDHB specialists and the Medical Physics Bio-engineering (MPBE) team has resulted in fewer return trips to the theatre for patients and savings of around $100,000.
Up until 2013 eye socket implants (to repair fractures caused by injury) were sourced from external engineering companies. The models were made locally and each one cost around $800. There was also a delay for the models to be made and returned to CDHB. Then the pre-bent socket plates were ordered from Europe. This cost an additional $1,000 per patient.
Jason Erasmus (Oral and Maxillofacial Surgeon) and Chris Lim (OMS Registrar) resolved to find a more economical and efficient way to meet this need. On hearing that the University of Canterbury had a 3D printer that could potentially make the custom models they requested funds to purchase a 3D printer for their department.
Then they discovered that our MPBE team already had one.
Jason and his team began working with Steven Muir from MPBE in early 2013 to produce their own custom models. Now the process is all in-house.
Images are taken of a person’s eye fracture and software used to produce a model via the MPBE 3D printer. The model is then used to customise a locally manufactured titanium orbital plate.
Jason and Chris are also using inter-operative CT scanning to decrease theatre time and drastically cut the readmission of patients for fine-tuning of their implant.
Traditionally, and still if the patient is being operated on at Christchurch Hospital, the patient receives eye socket surgery then gets a CT scan the following day to see if the implant was fitted correctly. If it wasn’t, the patient has to go back into theatre to have the implant adjusted.
Now, if the patient is operated on at Burwood Hospital (which has an in-theatre CT scanner), patients are scanned on the operating table as soon as the implant is fitted. If it is not fitting properly it can be adjusted there and then, before the patient goes into recovery.
“If you add up the savings in production costs and calculate the savings in theatre time the average cost for each patient is reduced by $2,500 – $3,000. We’ve done forty operations over the last 18 months at Burwood Hospital using these new technologies. None of these patients have had to return to surgery for adjustment. We estimate we’ve saved more than $100,000 and saved our patients time, risk of another anaesthetic, inconvenience and extended recovery time,” says Jason.

Page last updated: 20 October 2018

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