In about a week, at the upcoming 94th Scientific Assembly and Annual Meeting of the Radiological Society of North America (RSNA), Siemens will roll out the Somatom Definition Flash, a new dual source, dual detector CT scanner. The machine is so fast that patients don’t have to hold their breath during chest scans, and the bed moves through the scanner at about twice the speed of conventional models, likely eliminating claustrophobia in most patients.
Some technical info about the scanner from Siemens’ press release:
The fastest scanning speed in CT (43 cm/s) and a temporal resolution of 75 ms, enable for example complete scans of the entire chest region in just 0.6 seconds. Thus, patients are no longer required to hold their breath during the exam the way they had in the past. At the same time, the Somatom Definition Flash operates at an extremely reduced radiation dose. For example, a spiral heart scan can be performed with less than 1 millisievert (mSv), whereas the average effective dose required for this purpose usually ranges from 8 mSv to 40 mSv. The new CT scanner will be available for sale in the first quarter of 2009.
The gantry (i.e., the X-ray detector system surrounding the bore) rotates about its own axis in just 0.28 s. It is this extraordinary rotational speed that enables a scan speed never before attained in CT (i.e., up to 43 cm per second) and temporal resolution of 75 milliseconds. The patient is moved through the CT tube more than twice as fast as with any conventional system. At the same time, scans acquired with the Somatom Definition Flash require a much lower radiation dose than conventional scans. While the average effective dose for a heart CT scanner ranges from 8 mSv to 40 mSv, the new Siemens CT scanner gets by with less than 1 mSv. In comparison: The X-ray radiation that everyone is exposed to each year from natural sources amounts to 2 mSv to 5 mSv. The dose values of the new Siemens CT scanner, thus lie far below those of an intracardiac catheter examination, thus opening up possibilities for using CT scanners for routine cardiological examinations.
Due to the high scanning speed, it is now possible to acquire scans of the thorax, the heart or both at the same time in fractions of a second. For example, thorax examinations now only require a scan time of 0.6 seconds. As a result, patients no longer have to hold their breath during the scan. This offers considerable advantages, especially in cases involving the elderly, children, emergency, and ICU patients.
It is also possible to perform whole-body scans extremely fast: For example, a person with a height of 6 feet 6 inches can be scanned in less than 5 seconds. Until now, such whole-body examinations took more than 10 minutes to perform from patient preparation to diagnosis. With the Somatom Definition Flash, this process is completed in just a few minutes. This represents an advantage, especially for emergency medicine since, until now, physicians often had to forego this examination method due to time pressure. Furthermore, it is no longer necessary to sedate children prior to the examination, since they no longer have to remain still. The high scanning speed also makes it possible to cover large areas measuring up to 48 cm with 4D imaging (3D plus time). The areas scannable using conventional systems are limited to a maximum of 16 cm due to the detector size involved.
A scan of the entire heart can be performed in only 250 milliseconds, which is less than half a heart beat. In addition, it is possible for physicians to reliably display a heart with a fast pulse or an irregular heart beat without using beta blockers, thus simplifying the workflow and yielding clinical and financial advantages. Owing to its high scanning speed, the Somatom Definition Flash also features new possibilities for performing CT examinations of the heart in the sub-mSv range. This represents a much lower radiation dose than is obtainable with conventional systems, which require doses ranging from 8 mSv to more than 40 mSv. For the first time ever, the heart can thus be examined at a radiation exposure level that is three times lower than the background radiation a person naturally absorbs in a year.
The second generation of Dual Energy imaging will introduce a new imaging quality. The contrast in CT scans will be increased without having to apply the higher radiation dose previously required. This is achieved via a new, selective photon shield which blocks unnecessary parts of the energy spectrum. It thereby provides improved separation of the two simultaneous scans with low and high photon energy, without causing a higher radiation exposure than would result from an individual, conventional CT examination with only one energy source. Thus, the Somatom Definition Flash can always provide a double contrast which, for the first time ever, can also be used to classify the chemical composition of tissues via a CT scan in routine daily work. Subsequently, It could also be used to reconstruct unenhanced CT images without contrast media not having to perform an additional examination.
Gene Ostrovsky, one of our editors, joined Dr Val Jones of Better Health in a conversation with Dr. André Hartung of Siemens about the new machine. You can read the interview or listen to the podcast at Better Health…
Press release: Flash Speed. Lowest Dose (.pdf)…