Improving Rotation Speed of CT Scanners

The newest generation of CT scanners performs routine very-low-dose cardiac scans, use more sensitive detectors, faster gantry speed rotation, and the latest generation of iterative and model-based image reconstruction software.

The advancement of CT technology has traveled largely predictable paths over the last two decades; from single-slice, to dual, to 4-, 8-, and 16-slice, doubling slice counts every few years into the current stratosphere of 320 or 640 slices per rotation. In spite of all the upward mobility in detector capabilities and reconstruction software algorithms, the 16-slice scanner has remained the most commonly used scanner for studies outside the cardiac space. Now, however, with greater availability on the secondary market and, consequently, lower pricing than ever, 64-slice scanners have become heir apparent to the title of industry standard.

The newest generation of CT scanners marketed today can perform routine, very-low-dose cardiac scans of 3 mSv or less. They use more sensitive detectors, faster gantry speed rotation, and the latest generation of iterative and model-based image reconstruction software. These technologies combine to enable low-dose scans to be made at diagnostic quality at dose levels that would not have been possible just a few years ago. These technologies are the industry’s response to years of criticism by physicians and the general public over the high X-ray doses previously needed for CT scanning. Plus, now with some emerging technologies, manufacturers are able to reduce the contrast volume dosage, which reduces the risk of complications with the patient’s kidneys. New CT scanners offer the ability to improve consistency of the outcomes of CT studies. Primarily, automation technologies are standardizing the way CT is performed in terms of the scan range and reconstruction, and automation is driving the increased standardization of CT outcomes, reducing the variability within those outcomes as well.

Technological Advances
New technologies such as fractional flow reserve (FFR)-CT, coronary plaque assessment, and CT perfusion imaging take CT beyond anatomic assessment to now allow physiologic assessment without the need for nuclear perfusion scans or invasive diagnostic angiography. Coronary plaque assessment can be laborious to do manually, but as advanced visualization software becomes more automated, it is believed that it will see greater usage.

FFR-CT. Among the most talked about advances is FFR-CT, which unlike invasive catheter-based FFR offers a completely noninvasive FFR assessment of not just a coronary segment, but the entire coronary tree. The technology currently takes several hours to return a result, but as that processing time is reduced, FFR-CT is widely expected to see increased usage in the coming years.

Tablet-based CT workflow platform. The new scanners can be operated via a tablet that can be used to control all routine and advanced examinations. The platform with a 128-slice can perform whole-body scans of up to 200 cm with a scan speed of up to 175 mm per second, and with the 64-slice can cover scan ranges of up to 100 mm in one second. A new X-ray tube in the platform allows users to adjust the tube voltage in 10-kV increments while keeping the tube current high.

Advanced spectral CT. Latest configuration of the spectral CT has faster reconstruction speeds and better visualization of bone marrow pathology. These faster reconstruction speeds have been shown to enable the imaging of up to 200 CT patients per day. The scanner’s ability to estimate electron density enhances tissue characterization, while a new radiation therapy planning couch and bariatric table permit larger patients to be scanned with increased positioning controls.

Ultra-high resolution. The CT scanner capable of resolving anatomy as small as 150 microns can provide CT images with resolution typically seen only in cath labs. The newly designed detector provides more than twice the resolution of current technology.

Liquid bearing X-ray tube technology. This new technology delivers 2× longer life. The CT system enables visualization of fine anatomic detail with 25 percent lower electronic noise. Scans can deliver tissue characterization, contrast dose reduction, metal artifact reduction, and quantitative information about chemical composition. Plus, they enable dose-neutral GSI and routine HD anatomic detail.

Rotation speed. Significant improvements have been made in the rotation speed of the gantry, which translates into faster temporal resolution to reduce motion blur, important for the heart and areas near the lungs. Rotational speed in some of the newer scanners is under 300 milliseconds, compared to 400–500 milliseconds with older-generation systems.

Mobile CT scanner. The new portable scanners feature directional wheels, maximizing mobility and allowing easier and quieter movement in small spaces. The latest advanced data acquisition system delivers a 50 percent increase in CNR versus other portable CT technologies. A small footprint is ideal for mobile use yet it has a 40 cm gantry opening for improved coverage of adult head and neck, and full-body pediatric scanning. The system also features an internal drive system, making portability less strenuous, while also offering smart-sensing collision avoidance software to maximize control and patient safety.

Metal artifact reduction software. The new software offers optional artifact reduction that can be adjusted and optimized according to the amount of metal present. It uses information from the original scan to eliminate additional imaging studies. An intuitive touch screen interface allows technologists to adjust for either moderate or complex metal content. The metal artifact reduction software can be activated prior to the scan or it can be applied after the original reconstruction is complete. Both the original and corrected images are always available to view and compare.

Improved resolution with smart photons. CT systems are limited by cross-talk based on their use of reflectors. In direct conversion photon-counting detectors, each photon creates a number of charge carriers in the semiconductor in proportion to the energy deposited. Charge carriers produced in the semiconductor follow electric field lines to prevent cross-talk, as a result of which, these detectors avoid the geometric inefficiencies in scintillator-photodiode detectors currently used in commercial systems and help achieve better spatial resolution.

Way Forward
Trends continue to show that physicians want a definitive diagnosis with the first scan. If they choose CT as the imaging modality, they want that modality to be able to tell them what the next steps in the patient’s treatment should be. The difficulty comes when there are indeterminate findings. If manufacturers can continue to reduce indeterminate findings and make CT the first and final imaging modality needed, it can help reduce costs while facilitating improved outcomes and greater patient satisfaction. The market will see continuous improvements in CT reconstruction techniques, which will continually improve image quality at low doses. Future trends will adhere to making spectral results a standard of care.

The biggest advances in CT scanners over the past few years have been the introduction of new dose-lowering technologies, easily upgradeable scanners to allow conversion to high-slice systems, and faster gantry speeds to freeze cardiac motion. Additionally, the concept of slices a scanner can image at once is less important today than the total anatomical coverage the scanner can image in one rotation. There are new procedures and new technology coming out faster than ever. Some specialties and areas of study will benefit greatly from high-end technology beyond even 64-slices, especially as more robotics is involved. No one knows what the next disruptor will be which will accelerate the circle of life in CT, but one can be sure it is coming.