Computed tomography [CT] is a medical imaging method employing tomography. Digital geometry processing is used to generate a three-dimensional image of the inside of an object from a large series of two-dimensional X-ray images taken around a single axis of rotation. The word "tomography" is derived from the Greek tomos (slice) and graphein (to write).

Toshiba CT Scanner

Computed tomography was originally known as an "EMI scan" because it was developed at a research branch of EMI, a company best known today for its music and recording business. It was later known as computed axial tomography (CAT or CT scan) and body section roentgenography. CT produces a volume of data which can be manipulated, through a process known as windowing, in order to demonstrate various structures based on their ability to block the X-ray beam. Although historically (see below) the images generated were in the axial or transverse plane (orthogonal to the long axis of the body), modern scanners allow this volume of data to be reformatted in various planes or even as volumetric (3D) representations of structures. Although most common in healthcare, CT is also used in other fields, for example nondestructive materials testing. Another example is the DigiMorph project at the University of Texas at Austin which uses a CT scanner to study biological and paleontological specimens. The latest CT scanners create detailed 3-D movies of entire organs in real time. The new scanners promise fast and accurate diagnoses in emergencies like strokes and heart attacks, offering patients the best treatment options.

 

Next Generation dynamic volume CT

Ten years and £300 million in the making, the Aquilion ONE (Toshiba) has been installed in a few hospitals globally with one in Edinburgh, Scotland (Partly sponsored by The Royal Bank of Scotland). Current CT scanners have 64 channels, each capturing a single cross-section slice of the body. The Aquilon One CT scanner has 320 channels, streaming 10 GB of information per second. Its gantry, the 2 meter tall cylinder housing the imaging sensors, spins so fast it generates 27 Gs, and takes just .35 seconds per rotation.

CT Brain Scan Above: Rendered in less than a minute by the dynamic volume CT, the red and green areas on the left side of the image show increased blood flow in and around a hyper aggressive brain tumor.

This type of CT can scan an entire organ in one swoop of the gantry. Doctors can see the heart pumping, or blood working through the brain after a heartbeat. This scanner's speed will significantly boost diagnosis time and treatment options.

Currently, doctors may perform a battery of diagnostic tests to confirm a heart attack i.e. - an ECG, a calcium study, CT angiography, nuclear testing and catheterization.

Diagnostic Tests can take from hours to days. Confirming a stroke requires similar evaluations, but the stakes are even higher: Not only is the window for treatment just a few hours long, the clot-busting drugs that could be used can also cause massive hemorrhaging if there's a misdiagnosis.

In 20 minutes, this next generation of CT is able to not only accurately diagnose a stroke or heart attack, but also gauge just how badly the tissue has been damaged.

A conventional CT scanner has a viewing window of just a couple of centimeters. To view a fist-sized organ like the heart, the machine's sensors must take a series of images that are then built into a single, often-distorted image. (Think of trying to snap a panorama of the Grand Canyon on your camera phone, then stitching the pictures together.) Dynamic images, like one of a heart completing a single beat, aren't possible, because it takes 12 to 15 seconds to complete a whole-organ scan.

We can now see areas of the brain that aren't getting enough blood and oxygen and are at risk for stroke. Since we can see what we couldn't see before, we can think of new treatments to prevent a stroke from happening.

The heartFuture applications of these scanners might reach even further: such as being used to determine the efficacy of cancer treatments. Today, anti-angiogenesis drugs, which halt the blood flow to a tumor, are the most advanced weapons in the cancer-fighting arsenal. But no one drug is universal because human anatomy is so nuanced, responses vary from patient to patient.

These latest generation CT scanners can scan and render a real-time image of your heart in the time it takes the organ to beat once. They can show how a widely spread cancer in the liver or pancreas, for example -is responding to a drug. From there, doctors will be able to create tailored treatments based on patient response.

Current CT scanners can provide some insight into whether a drug is working to shrink a tumor's blood supply, but their limited views may create uncertainty.

The introduction of dynamic volume CT marks an important milestone in the history of computed tomography. This is the culmination of a decade of dedicated research and establishes a new frontier in CT imaging, offering advanced applications that can significantly enhance patient care while reducing the cost of healthcare worldwide.

 

Imaging the heart, brain or pancreas in a single rotation

The wish of medical professionals for the ability to scan an entire organ in one rotation and hence in a fraction of a second, has now become a reality. The dynamic volume CT boasts an anatomical coverage of 16cm in one rotation, thanks to its array of 320 ultra high resolution 0.5mm detector elements. This innovation means it is now possible to image an entire human organ such as the heart, brain or pancreas in a single rotation. Currently, it takes an average of 7 to 10 rotations to image a human heart, and 7 rotations for the brain.

This ability to carry out a complete examination in just 350 milliseconds eliminates the need to reconstruct data from several points in time, significantly enhancing accuracy and diagnostic confidence. In the case of a cardiac scan, medical professionals using this scanner will see clearer images with perfect time registration.

 

Real-time 3D information of organ function

The dynamic volume CT technology enables medical professionals to view crucial information such as blood flow (arterial and venous) and function in the heart, brain, joints and other parts of the body.

The resulting functional images of the scanned area is in effect similar to a real-time video of the organ(s). Real-time whole organ dynamic volume analysis was previously unavailable in any modality (CT, MRI, Ultrasound), and is a quantum leap in imaging accuracy.

This reduces the need for additional (sometimes duplicative) tests and invasive procedures Patients exhibiting symptoms of heart conditions may be given an ECG, calcium study, CT angiography (CTA), nuclear test and catheterisation before a diagnosis is made. This process typically takes a few days. Patients exhibiting symptoms of stroke may be given a CT scan and MRI (if the former proves inconclusive). The time-to-diagnosis may take a few hours.

With this technology, we may soon be able to not only assess the coronary arteries, the most common site of cardiac disease but also acquire additional information about other aspects of cardiac anatomy and function.

There is also a possibility that we will be able to evaluate and assess plaque and help determine the groups of patients which could be at highest risk for a cardiac event using this latest generation of CT technology.

 

Sources:
www.wired.com/gadgets/miscellaneous/news/2008/04/Toshiba_CTScanner
en.wikipedia.org/wiki/Computed_tomography
www.medical.toshiba.com/Products/CT/DynamicVolume/DynamicVolumeCTCoverage.aspx
news.bbc.co.uk/1/hi/scotland/edinburgh_and_east/7416732.stm

 

Compiled and Edited by John Sandham IEng MIET MIHEEM
May 2008

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