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Temporal resolution optimization in cardiac imaging

White Paper
Philips CT Clinical Science Philips Healthcare

Philips adaptive multicycle reconstruction algorithm adjusts to the patient's varying heart rate to deliver the best temporal resolution (as low as 42 mseconds1) in true 3-D cone beam reconstruction for stable, clear cardiac imaging.

Explanation

Other vendors/scanners require a consistent number of heart cycles to complete an entire reconstruction. When the information is not present or has been interrupted by movement, breathing, arrhythmias, etc. the surrounding data is interpolated or blurred to "fill-in" what is missing. This creates an obvious interruption in the contiguous flow of information and degrades the resulting image (Figure 1).
Figure 1 This image from a competitive system clearly shows the effect of heart rate changes when processed
using single cycle reconstruction.
Figure 1
This image from a competitive system clearly shows the effect of heart rate changes when processed using single cycle reconstruction.

 

Philips uses an adaptive multi-cycle reconstruction technique2,3, information from a varying number of cycles can be used within a single axial slice, and, thus no void in information is present.

 

Of course, the same physiological changes - breathing, movement, and arrhythmia - may occur when scanning on a Brilliance scanner. These effects are mitigated using an adaptive multi-cycle reconstruction technique that reconstructs a more complete volume of information.

 

The resulting image is a true representation of the anatomy and allows for more accurate tracking of the coronary vessels on the MPR, curved MPR and volume rendered images. This reconstruction method greatly reduces the banding - or "stair-step" - artifact that is frequently seen on other systems. Optimizing each and every temporal resolution window of information shows the actual delineation of each voxel. However, a fine line may result where the temporal resolution varies widely from one voxel to the next. Because this technique does not 'blur' the lines between the voxels, or over large areas of voxels, an authentic reconstructed image is displayed (Figures 2 & 3).

 

Removing these windows using the exact same cycles for the entire axial image will give the worst case temporal resolution. Instead, Philips gives each window the best case temporal resolution, sometimes resulting in image blocks caused by this phenomenon.

Figure 2 A fine line may appear if significant patient
movement occurs during the transition from one
heart cycle to the next heart cycle.Figure 3 This MPR image shows the transition
between windows of varying temporal resolution.
Figure 2
Figure 3
A fine line may appear if significant patient movement occurs during the transition from one heart cycle to the next heart cycle.
This MPR image shows the transition between windows of varying temporal resolution.

 

What affects image quality?
  • Voluntary - (Breathing) or Involuntary - (Diaphragmatic flutter) motion
  • Rapid changes in heart rate between two heart cycles (i.e., atrial fibrillation
  • High gradient differences between data from different heart cycles (Example: ECG lead in scan field - Sharp Z gradient may increase variance between temporal resolution optimization windows).

 

How do you achieve a more uniform reconstructed volume?
  • Coach your patient to avoid voluntary patient motion
  • Avoid placing ECG leads within the scan field
  • Try reconstructing a different phase of the cardiac cycle
  • Assess ECG signal for potential arrhythmia and adjust using "arrhythmia editing"

 

Philips users may or may not have noticed a fine line on an image. This is known as temporal resolution optimization. This phenomenon may not be noticeable to the human eye and alternatively; it may be noticeable, but in either case it is not critical to the application.

 

Philips Brilliance CT, featuring proprietary Rate Responsive CVCT technologies, is uniquely designed to adapt to a patient's physiology and overcome the many challenges that unpredictable heart rates and rhythms can present. These exclusive technologies identify any desired physiological state of the heart irrespective of the variations in the heart rate during the scan, ensuring more accurate data is collected and making this an ideal diagnostic tool for most cardiac patients.

 
References

  1. Manzke R, Koken P, Hawkes D and Grass M; "Helical cardiac cone beam CT reconstruction with large area detectors: A simulation study"; Phys. Med. Biol. 50 (2005) 1547-1568.
  2. Manzke R, Grass M, Nielsen T, Shechter G, Hawkes D; "Adaptive temporal resolution optimization in helical cardiac cone beam CT reconstruction"; Med. Phys. 30 (12), 2003: pp.3072-3080.
  3. Vembar, M; Walker, MJ; Johnson, PC; "Cardiac imaging using multislice computed tomography scanners: technical considerations"; Coronary Artery Disease 2006, 17:115-124


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White Paper
Brilliance 16 Power, Brilliance 16-slice, Brilliance 40-channel, Brilliance 64-channel, Brilliance 6-slice / 10-slice
3D, Brilliance v2.0, Brilliance Version 1.2, Cardiac, MPR, pediatric cardiac, prospective, Rate Responsive, resolution, retrospective
 

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