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Evolution of reconstruction performance

White Paper
Philips CT Clinical Science Philips Healthcare

Quantifying performance gains and clinical benefit of Philips CT reconstruction hardware advances

 

The latest evolution in RapidView reconstruction technology is a further proof point in Philips CT's ongoing pursuit of delivering world-class performance to customers. The adaptation of the latest in processing technology, Quad Core processors, and reconstruction algorithm enhancements enable 74% of the Brilliance CT 64-channel scanner's factory protocols to be completely reconstructed in less than 60 seconds. The benefits realized by continual hardware and algorithm advancements include improved department productivity, enhanced image quality, additional flexibility in acquisition techniques, and time to diagnosis.

 

With the evolution of CT technology, some traditional bottlenecks in CT workflow, such as acquiring data, have essentially disappeared. But, as existing bottlenecks disappear, new bottlenecks can emerge to replace them. In many institutions reconstruction time has posed a new constraint on CT productivity. Patients remain on the scanner while department staff verifies the acquisition has the correct coverage, the correct contrast uptake in CTA procedures, and makes sure that the exam does not require a delay phase to help the radiologist determine the proper diagnosis. For these reasons, and more, reconstruction time is tying up the CT department.

 

First, a review of the basic principles affecting reconstruction performance to set the foundation for understanding the true scope of the advancements brought forth by Philips. Namely we will look at total reconstruction time (TRT) verses image per second (IPS), and then explore reconstruction performance from a hardware and software algorithm standpoint.

 

Total reconstruction time

 

Two important components determine total reconstruction time: time to first image (TTFI), and images per second (IPS). Each one of these two metrics is independent of the other and represents opportunities for improvement. To underscore the impact of these two measures, look at a typical scanning scenario.

 

An acquisition is started (X-ray on) at time t1 and the first image is reconstructed at time t2. Images continue to be reconstructed up until time t3 at which time X images have been reconstructed.

 

TTFI is computed by the time difference between t2 and t1 t2 t1.

 

Using the scanning scenario described above IPS would be calculated as:

IPS = X-1/t3 - t2

 

As shown in this formula, the time between t1 and t2 is not taken into consideration when calculating IPS, thus the importance of taking TTFI into consideration when evaluating the reconstruction performance of a system.

 

TTFI becomes increasingly important to the overall reconstruction performance of a system as either the IPS increases or the scan length decreases. For example, the standard pediatric protocols TTFI makes up 31.3% percent of the total reconstruction time. The scan lengths of this type of procedure are inherently shorter than the other procedure types and thus the large contribution of TTFI to the total reconstruction time. Similarly, head exams represent another type of procedure that due to short scan lengths has a higher TTFI contribution of the total reconstruction time at 28.9%.

 

The TTFI chart shown below describes the percentage of the total reconstruction time associated with the TTFI. The average contribution for TTFI for all helical factory protocols is 19.3% of the total reconstruction time. Interestingly, the range of contribution is quite wide. In abdomen protocols, for example, TTFI makes up 10.1% of the total reconstruction time, and for pediatric protocols TTFI makes up 31.3% of the total reconstruction time. It is evident that judging reconstruction performance on IPS alone is not sufficient as it doesn't compensate for TTFI which represents a major percentage of the total reconstruction time. True reconstruction performance should only be measured as a function of total reconstruction time (T3-t1).

 

Reconstruction performance

 

Reconstruction performance is dependent on two components: hardware performance and algorithm performance. This next section will focus on discussing the basics of each component as well as the tradeoffs that were made in using the new found performance.

 

Moore's law

Moore's law describes an observation that the number of transistors that can be placed on an integrated circuit will double approximately every 18 months. This law has been informally translated into saying that the speed of computers will double every 18 months. Moore's law is very important in respect to CT reconstruction technology because the algorithms behind reconstruction are computationally heavy; i.e., the faster the computer the faster the reconstruction.

 

To take advantage of Moore's law, reconstruction hardware must be continually updated. Continuous adaptation of the latest computer technology is a philosophy held by the CT reconstruction development team. This philosophy is exemplified by the technology migration which has occurred in the Brilliance CT 64-channel RapidView reconstruction hardware. When the Brilliance CT 64-channel was introduced it exploited the most advanced processer on the market, a 3.06 GHz processor. As the processor's manufacturer continued to innovate in accordance with Moore's law, the reconstruction platform evolved, adopting a 3.6 GHz processor which brought significant benefits. The latest advancement in processor technology is a Quad Core processor. This has become the foundation of RapidView reconstruction hardware. This continued commitment to adopting the latest processor technology, and making it simple to upgrade existing installed base scanners, sets Philips apart.

 

Reconstruction algorithms

The underlying algorithms for reconstructing images from RAW data are complex and computationally heavy; with the advances in wide area coverage the computational power these algorithms demand has only increased. In the field of reconstruction algorithm development there are always trade-offs to be made when choosing algorithm techniques. Typically these trade-offs exist between final image quality and the time it takes to reconstruct the images. Filtered back projection is the most used technique in the CT industry. This method of reconstruction involves a number of inherent assumptions which simplify the complexity of the reconstruction process, allowing images of high quality to be produced in a reasonable amount of time. There are known algorithms that differ significantly from the ubiquitous filtered back projection method which theoretically would produce improved image quality, but there are tradeoffs when using them. An example of such a technique is iterative reconstruction which is fundamentally insensitive to noise, and has the capability of reconstructing an optimal image from incomplete data. These algorithms have not been adopted by the CT industry because they are so computationally heavy that system performance would no longer be measured in IPS, but in seconds per image, or even minutes per image. Using these algorithms would mean waiting hours, or even days, for a study to be reconstructed. This is completely impractical since that the data acquisition process takes only seconds.

 

Use of processing power

With each evolution of the underlying reconstruction technology new opportunities arise, and selecting the appropriate use of this new found processing power has many challenges. Developers must carefully consider the balance between improving total reconstruction time and performing more complex reconstruction techniques to improve image quality. This careful design balance can be easily seen in the latest generation of RapidView technology. Inspecting the total reconstruction time of the most routine protocols demonstrates how Philips has optimized the processor technology and reconstruction algorithms to deliver performance improvements and improved image quality. Displayed in the table to the right are some of the improvements found in the new generation of RapidView reconstruction. Clearly there are significant differences in the performance improvements realized across the different protocols.

 

Realized clinical benefits

 

Improved system productivity

Many enhancements are realized in the latest generation of RapidView reconstruction. These enhancements significantly add to the clinical value of the Brilliance CT 64-channel scanner. With the improved processing power and algorithm optimization RapidView reconstruction has dramatically improved system productivity. The median total reconstruction time of the factory protocols has improved 37% since the introduction of the Brilliance CT 64-channel scanner. This improvement enables 74% of the factory protocols to be completely reconstructed in less than 60 seconds.

 

Before releasing the patient, it's important for technologists to verify that the acquisition has covered all of the intended anatomy, that they captured the proper contrast enhancement in case of CTA studies, as well as ensuring the patient does not require a delay phase to assist in ruling out specific diseases. The latest generation of reconstruction technology allows the technologist to make these important clinical determinations rapidly. This realized improvement in total reconstruction time enables technologists to quickly verify that the acquisition was successful, and subsequently spend a greater percentage of a total procedure time with the patient, improving the patient experience and improving the productivity of the CT scanner. Shortened exam times quickly reduce backlog and free up capacity for added procedure volumes in the department.

 

As shown in the chart above the total reconstruction time has improved significantly with the introduction of the third generation of Philips RapidView reconstruction technologies. The total reconstruction time for head protocols has, on average, improved by 48% over first generation technology. Looking at all protocols the total reconstruction time has improved by 26% over the first generation of RapidView reconstruction.

 

Enhanced image quality

Image quality is a function of many components. These components can be grouped into three different themes: the patient, the system's user, and the system's technology. The patient has several characteristics that effect image quality: Voluntary patient compliance (patient movement, breath-hold compliance, etc.), involuntary patient compliance (heart rate, arrhythmias, etc.), and patient size. The system's user has significant control over the image quality of the system: Proper coaching of the patient, selecting the appropriate protocol, ensuring the correct parameter selection to match the patient's physiology, matching the injection protocol with the patient's physiology and selected protocol, and insuring the patient is properly centered. The third component to image quality is the CT system's technology. At a sub-system level this means X-ray tube, detector, and reconstruction technologies. All three of these pieces of technology need to function in unison in order to output images with good image quality. In summary, achieving the optimal image is a complex task involving many different aspects. Philips offers many different options to optimize these different components, but in the spirit of this paper we will only delve into the CT scanner's reconstruction technology.

 

The hardware performance gains realized in the new RapidView reconstruction platform are significant enough to give the development organization options on what to do with the performance: produce images with higher image quality, reduce the total reconstruction time, or both. This important design decision has to be made for each procedure type individually. Determining the optimal approach for each procedure type was obtained from careful analysis of the demands of today's clinical environment. This process led to many different approaches to using the gained processing power. Some procedure types were optimized to improve image quality while others received significant improvements in total reconstruction time, while maintaining existing image quality standards.

 

New flexibility

The significantly enhanced performance available in the new RapidView reconstruction with Quad Core processors provides CT departments with additional flexibility when establishing the departmental standard for quality of care. Acquisition parameters (such as pitch) contribute significantly to the resultant total reconstruction time. There are always specific combinations of acquisition parameters that result in improved image quality. The challenge with these ideal combinations of acquisition parameters is that resulting reconstruction time prohibits their use, i.e., the image quality gains do not offset the total reconstruction time penalty.

 

With gained performance of the RapidView reconstruction, CT departments can now optimize their acquisition protocols for image quality with no reconstruction time penalties. Post optimization, CT departments may even experience reduced overall total reconstruction time due to the significant performance improvements realized by the Quad Core processors.

 

The additional flexibility the latest generation of RapidView reconstruction brings to a CT department can be used to improve radiologist productivity, while at the same time improving quality of care. With the added reconstructed performance it is now possible to request additional reconstructions without negatively impacting the scanning operation. The benefit of additional reconstructions is that each reconstruction can use a different filter such as a bone filter or a soft tissue filter. While this produces more data to interpret, it can improve the radiologist's productivity, as each set of data is tailored specifically for their current interpretation need. This simplifies the reading process. The tailored data sets also improve the patient's quality of care as the radiologist is always reviewing the patient's data in its ideal form, reducing the likelihood of missing a critical piece of information.

 

Improved time to diagnosis

Improved processing performance of RapidView reconstruction enhances the workflow in a trauma situation by reducing the time to diagnosis. In trauma situations, where clinicians need information as fast as possible, seconds count. The improved total reconstruction time realized in this generation of reconstruction technology allows clinicians to access the images faster, allowing the diagnosis to be made sooner and ultimately for the treatment to be administered more quickly. Access to the images also enables quicker verification of a successful acquisition, which allows the patient to be moved to the next stage of the trauma treatment procedure.

 

Since images are reconstructed individually, TTFI becomes a very important statistic in emergency situations, as clinicians can begin interpreting results before the entire study is reconstructed. In trauma situations, where seconds count, this ability can go a long way towards saving lives. The newest version of RapidView reconstruction enables significant improvements in TTFI. Inspecting the TTFI improvements graph below clearly demonstrates the significant improvements over previous generations of RapidView reconstruction. Looking at all factory protocols you can see an outstanding improvement of 43% over the first generation of RapidView reconstruction. Even more incredible is the 68% improvement realized by cardiac protocols when compared to the first generation of reconstruction technology. These improvements indicate that physicians can start making their diagnosis earlier, leading to better outcomes for patients who are in time critical situations.

 

Conclusion

 

Philips has made significant improvement to its RapidView reconstruction unit for the Brilliance CT 64-channel scanner.

 

  • 74% of the routine protocols will be reconstructed in less than 60 seconds
  • 37% improvement in the median reconstruction time for routine protocols
  • 43% improvement in TTFI for routine protocols
  • 68% improvement in TTFIs for routine cardiac protocols

 

These improvements translate into improved patient care, improved department productivity, enhanced image quality, additional flexibility in acquisition techniques, and improved time to diagnosis for the clinician.

 

Philips has a well established commitment to practical, affordable technology migration, making sure all customers have easy access to the innovation needed for continuous improvements to departmental productivity and clinical care.



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White Paper
Brilliance 64-channel
abdomen, Body, brain, Brilliance v2.0, Cardiac, chest, emergency, FBP reconstruction, Head, helical, image quality, Neuro, Pelvis, RapidView, reconstruction, trauma, Vascular, workflow
 

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