Spectral Imaging

The first quantitative dual energy CT on the market. Gemstone* Spectral Imaging (GSI), an innovative technology that uses fast kV switching dual energy acquisition technology coupled with a fast sampling, low afterglow and high light output scintillator detector to produce near perfectly registered dual energy. This data enables projection based material density image generation and the derivation of beam hardening reduced monochromatic spectral images.


Gemstone Spectral Imaging (GSI) improves image quality over conventional imaging techniques due to higher contrast to noise ratio (CNR), reduced beam hardening artifacts, enhanced material separation, and quantitative material information all at a full 50cm field of view.

GSI provides information about the chemical composition of body materials, allowing the user to separate calcium, iodine and water to aid in the characterisation of pathology. 

A new spectrum of information and abilities across areas of clinical diagnosis including:

  • Quantitative lesion characterisation 
  • Beam hardening reduction
  • Enhancing contrast quality with monochromatic spectral image
  • Virtual non contrast like images
  • Enhanced coronary visualisation in the presence of calcification
  • Beam hardening reduced myocardial perfusion assessment

GSI is a unique dual energy technique that uses rapid kV switching and Gemstone Detector technology to acquire and generate material density data. Both high and low energy data sets are acquired simultaneously for near perfect anatomical registration throughout the full 50cm field of view.

This data can be used to separate materials and derive monochromatic spectral images using a projection-space reconstruction algorithm.

GSI provides information about the chemical composition of body materials. This capability enables the user to easily separate calcium, iodine and water to aid in the characterisation of pathology.

Gemstone Spectral Imaging can subtract iodine from images to generate a virtual non
contrast-like image.

GSI Cardiac

Built on the unique Gemstone Spectral Imaging technology, enabled by ultra-fast kV switching, GSI Cardiac provides enhanced visual assessment of coronary vessels. The ability to alternate two kVp energies at 0.25msec leads to unprecedented temporal registration (over 165 times faster than other Dual Energy technology) vital for coronary vessel imaging.

Generating material density and monochromatic data allows for both separating materials like calcium and iodine and interactively changing monochromatic energies, which enables physicians with the ability to enhance the visual assessment of of coronary vessel patency in the presence of calcification.

Featuring GSI Cardiac, the Discovery CT750 HD FREEdom Edition* will allow you to go beyond today's clinical information with plaque material composition assessment and accurate perfusion calculations.

A common IQ artifacts in CT myocardial perfusion imaging is a beam hardening shadow that appears in the lateral Ventricular wall. Using GSI Cardiac, beam hardening artifact can be reduced and iodine concentration can be quantified in the myocardium which is important for accurate perfusion calculations in rest or in stress conditions.

GSI Cardiac may also provide information to assist with plaque material composition assessments via the HU Spectral Curves.

Dose Neutral

Designed for dose neutrality the FREEdom Edition* brings together two of it's key technologies GSI and ASiR*.  The new FREEdom Edition presets and flexible GSI ASiR settings achieve dose neutrality between GSI and SECT.

Also when compared to SECT at similar dose levels GSI produces better contrast to noise ratio which may improve your diagnostic confidence.


1.Obtained by ICRP using a chest factor of 0.014DLP.


Exclusive to the Discovery CT750 HD, the spectral image is created as though it comes from a single energy (keV) source. Individual spectral images can be derived from 101 user-selectable energy levels. This approach enables image contrast optimization, accurate CT numbers and up to a 50% reduction in common beam hardening artifacts - features that together allow physicians to diagnosis confidently and quickly. 

Utilising lower energy spectral images allows for better contrast differentiation, thereby accentuating subtle contrast differences.

Clinical Images



Renal Stone Using GSI- June 2011

  • Date Created: 7/3/2012
  • Document ID: DOC0982416

GSI Kidney Stone Cases Study

  • Date Created: 7/9/2012
  • Document ID: D0C0893003

GSI Lesion Characterization Case Study

  • Date Created: 7/9/2012
  • Document ID: D0C0892988

GSI Pulmonary Embolism Case Study

  • Date Created: 7/9/2012
  • Document ID: D0C0893007

GSI Metal Artifact Reduction Case Study

  • Date Created: 7/9/2012
  • Document ID: D0C0892994

Emergency Applications in Musculoskeletal

  • Date Created: 7/3/2012
  • Document ID: DOC0982416

Value of GSI

  • Date Created: 7/3/2012
  • Document ID: DOC0982416

Musculoskeletal Imaging

  • Date Created: 7/3/2012
  • Document ID: DOC1062022