Which scanner: Which is the more advanced and best all around scanner….the GE CT750 or the Siemens Flash? If you could only buy one as your only scanner which would you buy? Are there any “must have” options?

Savvas Nicolaou,  MD, Vancouver General Hospital, University of British Columbia:

Both are great scanners however overall I would purchase the Siemens Flash scanner because of its great versatility. It allows you many more options on scanning many different types of clinical scenarios.

Cardiac: The Flash scanner allows you to scan with and without b blockers given the 75 msec temporal resolution that can be advantageous in patients that you cannot use b blockers ie asthmatics, COPD, extremely high heart rates.
You have the possibility in scanning prospectively without b blockers thus lowering the dose, you can scan in Flash mode if the heart rate is below 65 beats per minute at doses less than 1 msv
You still can scan spiral for unpredictable heart rates
You also now have the possibility in doing perfusion dynamically or utilizing dual energy for assessing ischemia
You can do a Flash triple rule out around 4 to 5 msv where most scanners require 15 to 20 msv

Thorax: You can dual energy imaging for pulmonary embolism assessing for perfusion defects, or you can sue the flash mode that allows you to also visualize the coronary arteries at the same time and limits motion that is useful for critical ill patients that cannot hold there breaths, this mode is also useful for pediatric patients as you do not need to use sedation to limit motion. By using dual energy you can better see aortic leaks for aortic stent graft assessment given the increased sensitivity at the 80 or 100 kv setting in dual energy mode.

Neuro: You can do whole brain perfusion under 5 msv
You can do dual energy imaging that allows you to quickly subtract the bones from the vessels allowing you to expedite your workflow in CTA’s of the head and neck and also this is very useful for arteries that have lots of calcified plaques as it allows you to subtract the calcium from the vessel wall.

Vascular: you quickly do whole body run offs in a matter of seconds with dual energy that allows you to see distal calcified vessels more clearly due to the pure bone vessel subtraction

Abdomen: You can use dual energy to better assess renal , liver pancreatic lesions and you can save dose from the virtual non contrast scan as you do not need a seperate non contrast scan. You can use dual energy to characterize renal stones separate uric acid from calcium stones.

MSK: You can use dual energy to asses for gout arthropathy also can use the Z sharp ultra high resolution mode to better analyze the bony anatomy at a resolution of 0.24 mm.
Bariatric patients: given the 100 kwatts dual generators and dual tubes you can increase your photon flux to obtain high quality images in these type of patients.

DOSE: Dose is always an issue you have 4D care dose to modulate the tube current adaptive collimation to decrease the dose form spiral scans, but you can also use X care dose to limit the amount of radiation anteriorly particularly to the breast and thyroid tissue. And now you have IRIS that can save dose up to 40 percent.

I think based on all of these advantages that have been tested clinically, the Flash scanner is the most versatile scanner on the market at the present time.

thank you
Dr Savvas Nicolaou

CT coronary angio – what is the normal range of calcium score?

Ralf Bauer,  MD, Clinic of the Goethe University, Frankfurt, Germany:

Dear Mr. Singh, thank you for your question!

But actually, it is not easy to answer. First, there is no real “normal” range. The clinical value of the Agatston score depends on a) the patients´s cardiovascular risk profile and b) if the patient is symptomatic or not.
The amount of coronary calcium needs to be seen in context of the patient´s sex and age, and what is “normal” varies with these parameters. There are age- and sex-adapted tables. A CS of >75.
percentile is considered abnormal. There is the old, traditional classification with 4 steps: Agatston Score of 0, 1-100, 101-400 and  >400. Significant coronary artery stenosis is considered to be very unlikely with a CS of 0, where a score of >400 is considered to represent a very high likelihood for significant coronary artery stenosis.
In asympotmatic patients it has been understood that an elevated CS represents an independent risk factor in addition to classic cardiovascular risk factors with incremental prognostic value.
In symptomatic patients, various different managment strategies have been proposed for patients with elevated CS up till now reaching from a combination of CS + invasive cath angio to CS + myocardial perfusion imaging. However, there have also been a couple of studies that showed no relation of elevated CS and the degree of coronary stenosis or the presence of a perfusion defect. This pretty much depends on the level of athereosclerotic risk of the investigated study population.

Most of all, it needs to be understood, that a negative calcium scoring scan does not exclude soft plaques and severe stenosis caused by them.
This is one of the reasons why in our institution we do not perform a stand-alone calcium scoring scan, but always do a coronary CTA, too.

I recommend a recently published excellent review article on coronary calcium scoring by Nucifora G et al in Cardiovascular Therapeutics 2010, doi: 10.1111/j.1755-5922.2010.00172.x

Best regards
Ralf Bauer

Does iterative reconstruction in general and IRIS specifically decreased blooming artifact from calcific plaque in coronary cta and to what extent. Is there a difference between the benefits derived from IRIS between its use with the Definition scanner versus the Flash?

Stephan Achenbach,  MD, University Hospital Erlangen:

IRIS reconstruction mainly reduces noise – in my experience – and may therefore contribute a little towards reducing blooming in the context of sever calcification. You are able to usse thineer slice recons with less penalty as far as noise goes. There should be no difference between the Definition and Flash.

Dear professor,
As I am a new learner of the DECT, I would like to know how the virtual no-contrast images be created? And is there any concrete calculation method?
thank you!

Sandra Halliburton, Cardiac Imaging Scientist, Cleveland, OH (USA):

Virtual non-contrast images can be generated using “Liver VNC” from Dual Energy software (syngo, Siemens).  The default settings of the Liver VNC can be modified to customize dual-energy image post-processing.

1. Measure attenuation (HU) of contrast agent in lumen in both 80 and 140 kVp images and calculate the ratio as HU_80/HU_140.  Replace the default “ratio” (default = 2) in the “Liver VNC” window with this new ratio value.
2. Replace the default maximum threshold value of 3071 (attenuation value above which voxels will excluded from processing) with a lower value (may be like 700 or 800). Ensure that contrast attenuation in 80 kVp is lower than this maximum threshold value.

Advantages of cardiac scanning with DSCT and flash scanning: can you let me know the cardiac scanning advantages of DSCT and Flash over other cardiac techniques like mri, spect, pet, invasive angio

Harald Seifarth, MD, Department of Clinical Radiology, University of Muenster, Germany:

The advantge of DSCT in cardiac imaging is the good temporal resolution. The temporal resolution of the Definition is 83 ms and in the Flash it is even 75 ms, providing good image quality at high heart rates (see paper). The Definition Flash also has a wide detector that allows to acquire the entire heart in only about 4 heart beats (depending on the size of the heart) in the step and shoot mode. The scan time usually is about 5 seconds.
The Flsh mode is a new scan mode that makes it possible to image the entire heart in only one heart beat. The trade off is that this mode can only be used in low heart rates. The big advantage however is that the dose is very low. Depending on the scan length, in some patients the dose is below 1 mSv.

How can we get the images twice faster altough the two tubes have different keVs?

Hello. I’m a radiology resident doctor in South Korea. First of all, sorry for my poor English.

I haven’t understood the basic principle of DSCT. My question is how can we get the images twice faster altough the two tubes have different keVs?

I read some articles that says attenuation, noise and contrast characteristics differ according to different keVs, therefore we can differentiate the contrast materials from bone using DSCT.

But how can we get the images faster, although the two tubes have different keVs (which makes the different HU results, noises and contrasts)? I mean, how is it possible to combine the images from each tubes into ONE set of images of ONE charateristics?

Thank you.

Hyun Woo Goo, M.D., Asan Medical Center, Seoul:

For dual energy CT, gantry rotation speed of 330 ms is used, which is different from cardiac application of dual-source CT. So it is not faster than usual scan mode. However, it is faster than any other CT systems with dual-energy scan mode.

Two x-ray tubes produce two different levels of tube potentials (kV or kVp). KeVs are not appropriate for polychromatic x-ray used in clinical CT systems. Monochromatic x-ray is used in synchrotron CT. To obtain comparable image noises of the two datasets, higher mA is used for a low kV (80 or 100). To produce dual-energy CT images, material decomposition algorithm is used and image-based method is used for combining the two image datasets.

For more information, I recommend a nice review article as follows: Johnson TR, Krauss B, Sedlmair M et al (2007) Material differentiation by dual energy CT: initial experience. Eur Radiol 17:1510-1517

Sincerely yours,

Hyun Woo Goo, M.D.

This question has also been answered by Anja Reimann, M.D. Read the article.

How can we get the images twice faster altough the two tubes have different keVs?

Hello. I’m a radiology resident doctor in South Korea. First of all, sorry for my poor English.

I haven’t understood the basic principle of DSCT. My question is how can we get the images twice faster altough the two tubes have different keVs?

I read some articles that says attenuation, noise and contrast characteristics differ according to different keVs, therefore we can differentiate the contrast materials from bone using DSCT.

But how can we get the images faster, although the two tubes have different keVs (which makes the different HU results, noises and contrasts)? I mean, how is it possible to combine the images from each tubes into ONE set of images of ONE charateristics?

Thank you.

Anja Reimann from the Department for Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Tübingen:

Dear Dr KoYH,

There are two different issues here.

First you can use both tubes at the same keV to reduce time resolution and increase your scan time by reducing the rotation needed to produce a picture from half turn to two simultaneous quarter turns. This reduces the time resolution and in the long run scan time, but as you correctly note this does not work with two different tube voltages.

But with the newest generation DSCT the tubes are not excactly in the same x/y plane so you get an interwoven spiral of data with either a single or two different tube voltages. You can increase the pitch significantly as the gaps are scanned by the other tube simultaneously. Due to the slight shift between the two tubes the full volume is still covered, but with almost double the coverage in z-axis compared to a first generation DSCT; the time resolution will stay at half a turn though. With high end interpolation it is possible to ‘fill in’ the missing data of each keV so you get two gap free sets of data with the effect of a reduced scan time AND at different tube voltages. Actually, its three data sets, as the two (80 and 140keV) are then combined to a virtual 120keV scan, too .

Hope this helps a bit.

Anja Reimann

This question has also been answered by Hyun Woo Goo. Read the article