Computed Tomography
Picture Perfect - Sharper images, less radiation

The four major players in Computed Tomography (CT) – Philips Medical, GE Healthcare, Siemens Medical and Toshiba Medical – have all recently announced key advances to their leading CT products.

Already at an exceptionally advanced stage of development, the top-end CT scanners offer images of the body’s internal organs unrivalled in their detail, quality and clarity.

This is leading to a significant evolution in diagnosis and treatment and is playing a key role in the progress of preventive medicine. The latest, most powerful scanners are enabling new clinical applications.

No longer do they just provide exceptional morphological data, they are now capable of providing functional imaging, such as cardiac and neuro perfusion imaging, similar to positron emission tomography (PET)-CT.

The quality of a CT image depends on the nature of the x-ray source and detectors, the number and speed of the measurements made, and the software applications used to reconstruct, display and interpret the data. As these scanners have progressively got more powerful, producing images with greater detail and clarity, so has the radiation dose increased.

At issue, then is the need to keep improving image quality, but decrease the radiation dose and this is where the major developer-manufacturers have made significant inroads. The competition is fiece.

Middle East Health looks at these advances in Philips’s Brilliance iCT, Siemens’s Somatom Definition AS, GE’s LightSpeed VCT XT and Toshiba’s AquilionONE.

The world’s first adaptive CT scanner installed



Siemens Medical recently installed the world’s first ‘adaptive CT scanner’, the Somatom Definition AS, at the Trauma Center of the University Hospital Erlangen in Germany.

Siemens claims the scanner has several unrivalled new features including computing power and gantry rotation speed. As its name implies – ‘AS’ stands for adaptive scanner – it can be adapted to a wide variety of procedures including trauma imaging, vascular imaging and oncology imaging.

Announcing the installation at Erlangen via an online web conference, Dr Bernd Montag, head of the CT division, Siemens Medical Solutions, said: “The Somatom Definition AS CT is fast, robust and reliable. It will provide an answer at all times.” He said this was the mission when Siemens designed and built Somatom Definition AS.

“We wanted the system to adapt to any patient – children, obese or claustrophobic patients, stroke or cardiac patients.

“The Somatom Definition CT scanner transforms itself into a stroke unit, a noninvasive cath lab, a therapy management tool for cancer patients, or an interventional suite – all according to the need of the individual patient,” said Dr Montag.

“All of these advances work to improve the quality and efficiency of healthcare while keeping the costs down.” Dr Michael Lell, assistant professor of radiology at the Institute of Radiology, University of Erlangen, explained some of the technical details.

“The Somatom Definition AS CT holds the record for gantry speed rotation – 128 slices in 0.3 seconds per rotation with a resolution of 0.33 millimetres,” he said.

Radiation dose

A key issue in CT is radiation dose. All CT vendors fall prey to unnecessary dose both before and after the spiral scan, which is a function of spiral multislice imaging.

As detector size and slice counts grow, this problem becomes more acute, particularly where older gantry designs are simply updated with newer detector designs to save cost for the manufacturer.

Siemens’ unique Adaptive Dose Shield addresses this issue by dynamically blocking the unnecessary dose before and after the spiral scan, ensuring that the only dose applied to the patient is dose that is clinically relevant.

Dr Lell explained: “Using a spiral scan, the scanner can use ECG pulsing to reduce dose to 7-8 millisieverts. Using a sequential scan, which is best at lower heart rates, the dose can be as low as 3.5 millisieverts.”

Full body scan

The Somatom Definition AS is the first scanner to combine dynamic components such as the Adaptive Dose Shield with a scan field of up to 200 cm and the wide 78-cm gantry bore. This enables fast and problem-free full body, head-to-foot scanning, which is especially beneficial for polytrauma patients.

The high temporal resolution of up to 150 ms – combined with extremely fast coverage with up to 128 slices per rotation – makes crystal-clear colour images possible, free of movement artefacts, of even the finest anatomical details. This permits, for example, highly accurate measurement of stenosis or precise planning for stent implantation.

Functional imaging

The Definition AS adapts to each patient’s clinical situation and also opens the door to new applications in CT imaging. Dr Montag pointed out that with its speed and high resolution the Somatom Definition AS “no longer just provides morphological data from its images, but can now start providing functional imaging, similar to PET-CT”.

A special feature of this CT is the Adaptive 4D Spiral which enables the Definition AS to address functional imaging (perfusion images of blood flow over time) specific to the organ being imaged.

This allows Siemens to offer information beyond simple perfusion and into phase contrast CT. In the case of a stroke, physicians can use whole-organ perfusion imaging not only for a small part of the brain, but for all of it. In a stroke situation, for example, the entire brain perfusion can be displayed.

With previous systems, only a portion of the affected organ could be imaged. “We hope we can diagnose stroke earlier with this CT. The earlier we get the patient to therapy, the better,” said Werner A. Bautz, MD, professor and chair of diagnostic radiology and director of the Radiological Institute at the University Erlangen- Nuremberg.

“The system can cover the whole brain in a single scan,” said Dr Lell. “Brain scanning previously had been limited to a few centimetres per scan.” Dr Montag said the computing power, equivalent to 200 high-end PCs, is unparalleled.


“It holds a number of records,” he said. “It can transfer wirelessly 8.5 gigabits of data per second. The spinning gantry produces 38 times the force of gravity. “None of this performance is matched by our competition,” he said. Dr Montag emphasised the adaptive capability of the Somatom Definition AS.

“This system really transforms itself into the gatekeeper in the Emergency Department, but it can be transformed into a non-invasive Cathlab, or for imaging systemic diseases or even a stroke unit.”

He added that it can be used in the minimal invasive therapy suite to provide treatment under CT guidance, where you can merge the 3D image with real-time guidance.

This will enable, for example, biopsies of suspicious tumour tissues to be performed for the first time with the help of 3D image guidance, making accurate needle positioning routine. In addition to its extraordinary performance, the Somatom Definition AS is able to adapt to the space constraints many facilities face.

It requires very little floor space, with an 18-m2 footprint. This allows the Definition AS to fit into rooms that have traditionally been too small for high-end CT scanners. The Definition AS will be available in 40-slice, 64-slice and 128-slice configurations.

● For more information visit: http://healthcare.siemens.com/ct_applications/definition_as/index.html


Brilliance iCT captures entire heart in two beats

Philips unveiled their 256- slice Brilliance iCT scanner at RNSA 2007 in Chicago in November.

This powerful scanner incorporates key improvements to two critical issues with CT, namely speed of image acquisition and radiation dose. The ‘i’ in iCT stands for ‘intelligent’. Philips’s says the Brilliance iCT’s exceptional acquisition speed enables it to capture an image of the entire heart in just two beats.

The machine’s x-ray emitting gantry can rotate four times in a single second, 22% faster than current systems. The detailed images provide 3D views of entire organs, such as heart or brain that can be rotated through any angle.

In addition, Philips says the scanner can reduce radiation dose by up to 80%. At the launch of the scanner Steve Rusckowski, CEO of Philips Medical Systems, said: “Our innovations are perfect demonstrations of Philips’ commitment to enable healthcare providers to devote attention to their patients, not just the technology.

The new Brilliance iCT scanner was designed to make the job of the clinicians easier and improve the experience of the patient.” Brilliance iCT features Philips Essence technology, consisting of new x-ray tubes, detectors and improved design elements.

The Brilliance iCT scanner is also designed to reduce patients' exposure to x-rays. In a retrospective study, the Wisconsin Heart Hospital, in the US, found that it had achieved an 80% dose reduction using the ‘Step & Shoot’ cardiac feature compared to previous exams using helical CT angiography techniques.

Speaking to Middle East Health, Walter van Kuijen, senior vice president Philips Healthcare, general manager Central and Eastern Europe, Nordic, Middle East and Africa, explained the ‘step and shoot’ method.



“The Step and Shoot cardiac acquisition is a prospective axial [as opposed to spiral] acquisition that enables the heart to be scanned in four shots over three steps in the Brilliance CT 64, taking advantage of the 4cm detector coverage in a single rotation,” Van Kuijen said.

“For the Brilliance iCT the same prospective axial acquisition is applicable but now with the wider 8cm coverage of the iCT the whole heart can be captured in two shots and a single step.

“As this is an axial acquisition instead of the conventional spiral acquisition mode of operation there is no overlapping radiation given to the patient meaning the patient dose is typically reduced for coronary artery evaluation by up to 80%.”
 

Toshiba unveils 320-slice CT scanner

At RSNA in November, Toshiba America Medical Systems unveiled their super powerful 320-slice CT scanner – the AquilionONE. The company says it is the first dynamic volume CT scanner due to its ability to capture a large volume – 16 cm – in a single gantry rotation.

“Dynamic volume CT marks an important milestone in the history of computed tomography,” says Doug Ryan, senior director, CT Business Unit, Toshiba America Medical Systems. Also at RSNA the company announced FDA clearance for the system, which they say clears the way for its commercial availability in 2008.

The system has recently been installed at Johns Hopkins University in Baltimore and Brigham and Women's Hospital in Boston in the United States. Worldwide installations also have taken place at Fujita Health University in Japan; Humboldt University, Campus Charité Mitte in Germany; and University Health Network in Canada.

Auntminnie.com reports that Toshiba has made a number of improvements to the Aquilion architecture including the “next generation of its Quantum detector technology, Quantum V, with 0.5-mm detector elements, as well as a new tube, called MegaCool V”.

Toshiba says that for the first time physicians can see not only a three-dimensional depiction of an organ, but can also use it for cardiac and brain perfusion studies as it captures the dynamic blood flow and function of those organs.

The AquilionONE can scan one organ – including the heart, brain and others – in one rotation because it covers up to 16 cm of anatomy using 320 ultra high resolution 0.5mm detector elements.

The company points out that this reduces exam time, as well as radiation and contrast dose, and dramatically increases diagnostic confidence. Auntminnie.com, the website specialising in radiology news, reports that the system produces 80% less radiation dose than a 64- slice model due to the elimination of overlapping CT slices by capturing large image volumes in a single gantry rotation.

This also eliminates stitching artefacts from the image. Toshiba claims that healthcare costs will be reduced because the AquilionONE reduces the need for multiple, duplicate tests and invasive procedures.

Toshiba says the speed and high image resolution of the AquilionONE is its great advantage, particularly with regard to patients with neurological symptoms, specifically related to stroke.

Workflow

Also at RSNA Toshiba showcased the workflow enhancements for the Aquilion CT product line, including:

● SURECardio Prospective gating software application that combines high-speed helical scanning with gated intermittent exposure to further reduce dose during cardiac examinations

● Variable Helical Pitch (vHP) scanning that allows non-stop helical scanning while performing multiple exams

● Optional higher-weightcapacity patient table (up to 295kg) to meet the needs for imaging a wide range of patients, from bariatrics to paediatrics

For patients exhibiting symptoms of heart conditions, diagnosis time can be reduced from days to minutes.

Typically, patients who come to the ER with chest pain are given multiple tests to identify the problem, including an EKG, calcium study, CT angiography (CTA), nuclear test and catheterisation.

Tests of this nature could take days to complete and would expose the patient to significant radiation and contrast dose. With the AquilionONE, a single comprehensive exam can give physicians all of the information they need to diagnose and treat the patient in less than 20 minutes and with significantly less contrast and radiation dose.

Toshiba’s development of the Quantum Detector technology platform made it possible to produce the industry's thinnest detector elements at 0.5mm with the industry’s best low contrast resolution.

In addition, this completely new system is equipped with innovative features such as the coneXact dynamic volume CT reconstruction.

GE looks to ‘go back to the future’

At RSNA in Chicago in November GE Healthcare showcased its new advances in CT under the umbrella of ‘High Definition (HD) CT technologies’. GE says it intends to incorporate these technologies into it next generation of CT scanners.

“HDCT technologies represent a dramatic departure from recent CT industry trends, but one that – at its core – is aligned with the real diagnostic goals that clinicians are demanding for their patients,” said Gene Saragnese, vice president of Molecular Imaging and CT for GE Healthcare.

“We’re reinventing CT to help them clearly see more detail. We’re working with new functional and time-based CT information that might help them know more. And we’re investing to provide them unprecedented diagnostic clarity using considerably less dose.

We believe HDCT technologies are transformational and we’re excited about the clinical possibilities that they may enable.” The new technology will aim to improve visualisation, data processing and reduce radiation dose.

Visualisation

GE says that trying to solve the paradox of a step-function improvement in image clarity while simultaneously reducing patient dose required going “back to the future” and returning to the fundamentals behind spatial resolution, low contrast discrimination and dose efficiency.

Believing that simply adding more slices or x-ray sources does nothing to improve image clarity, GE engineers and scientists are working on completely revamping the entire CT imaging chain – from the x-ray tube through the detector and data acquisition system – even rewriting the way images are reconstructed for the first time since CT was invented.

As a new foundation, GE materials scientists are reformulating new CT detector material for the first time in 20 years. This new scintillator material is, literally, a gem. It’s based on the brilliant garnet gemstone because of its unique optical properties.

When modified to enhance its x-ray-scintillating behaviour, the “GE Gemstone” CT detector is being designed to provide significant improvements to x-ray conversion speed and other properties required to support step-function improvements in spatial resolution.

Data processing

Through the introduction of projection-based dual energy data processing, GE developers have been reconstructing monochromatic CT images that show reduced beam-hardening artifacts, and subsequently more accurate CT numbers.

This potentially fulfils a dream of truly quantitative CT exams “The clinical potential of dual energy CT may finally be unleashed by HDCT technologies’ ability to natively support monochromatic whole body helical exams; potentially providing more quantitative diagnostic content, virtually free of temporal misregistration and beam-hardening effects,” said Saragnese.

“Potential clinical applications may include calcium/iodine separation, accurate auto-bone removal in 3D assessments, material decomposition, and artifactfree images in areas previously rendered less diagnostic by beam- hardening.”

GE engineers are also working to dramatically expand coverage of fastmoving cardiovascular events to whole organs through an innovative volume helical shuttle technique.

This HDCT technology has been under clinical investigation for over a year, and is recently demonstrating 4D coverage of up to 250 mm of thoracic anatomy.

It extends helical scanning with a back-andforth pattern, modulating energy levels during acceleration and deceleration to minimise patient dose.

More critically, this HDCT technology potentially mimics clinically-relevant coverage over a volume that would have required the equivalent of up to a 400-slice detector.

Dose reduction

With the aim of reducing patient radiation dose GE research scientists are working at rewriting the basic way images are reconstructed.

Their approach differs from traditional filtered back-projection techniques in that statistical noise profiles are utilised in an iterative manner to extract additional image clarity and suppress noise.

When coupled with ongoing industry advances in computing power, these Adaptive Statistical Iterative Reconstruction (ASIR) algorithms are showing considerable promise in providing images of higher clarity and at lower patient dose – while still maintaining reasonable diagnostic workflows for the reading physician.