Dual-energy computed tomography (CT) makes it possible to remove bones and intraluminal plaques from angiography datasets on the basis of spectral differentiation separating iodine from calcium. The objective of this study was to evaluate the feasibility and efficiency of this technique by comparing maximum intensity projections (MIP) created with different bone removal techniques: (a) dual-energy bone removal (DEBR); (b) purely software-based bone removal without manual corrections (SBBR – MC); and (c) manually corrected software-based bone removal (SBBR + MC). A further aim was to evaluate the dual-energy-based plaque removal tool.

MATERIALS AND METHODS

Fifty-one patients underwent dual-energy CT angiography of the lower-extremity arteries on a dual-source CT scanner. CT parameters were tube potentials, 140 and 80 kVp; exposure, 80 and 340 mAs/rot; and collimation, 14 x 1.2 mm. Bolus tracking was used in the descending aorta for timing (Ultravist 370). Bones were removed from the datasets using the 3 techniques and MIP datasets were generated. Two experienced radiologists assessed image quality ((1) correct removal of bones and preservation of vessels without artificial truncation, stenoses or occlusions of arteries; (2) minor errors with residual bone in the dataset or removal of side branches; (3) significant errors impeding diagnostic evaluation), number of vessel segmentation errors, and number of nonremoved bones. Additionally, time for MIP-generation was measured. The plaque removal tool was applied to DEBR MIPs and the outcome was rated as positive, neutral, or negative.

RESULTS

DEBR showed better image quality than SBBR (p < 0.05; median image quality DEBR: 1; SBBR – MC: 3; SBBR + MC: 2). Less vessel segmentation errors occurred in DEBR (p < 0.05; median DEBR: 0; SBBR – MC: 5; SBBR + MC: 1). The number of nonremoved bones was not significantly different between DEBR and SBBR + MC, but significantly higher in SBBR – MC (median DEBR: 1; SBBR – MC: 2; SBBR + MC: 0). Time for generation of MIPs was lowest for SBBR – MC (p < 0.05), but also DEBR was significantly faster than manually corrected SBBR (DEBR: 160 +/- 16 seconds; SBBR – MC: 95 +/- 12 seconds; SBBR + MC: 373 +/- 69 seconds). The plaque removal tool lead to an improvement of image quality of the MIPs and a better depiction of the residual lumen in 43 %.

CONCLUSION

DEBR provides significant advantages, even over manually corrected SBBR. As it works completely automatically, it can effectively help to cope with the data load of CT angiography exams. Furthermore, it enables the removal of intraluminal plaques, which provides a benefit for the estimation of the residual lumen.

Authors: Sommer WH, Johnson TR, Becker CR, Arnoldi E, Kramer H, Reiser MF, Nikolaou K.

Full text: Invest Radiol. 2009 May;44(5):285-92

A total of 256 CT examinations were evaluated (Siemens, Sensation 16: n = 90; Siemens Sensation 64: n = 91; Siemens Definition: n = 75). Mean Hounsfield units (HU) were measured in the cavum of the left ventricle (LV), the ascending aorta (Ao), the left ventricular myocardium (My) and the proximal part of the left main (LM), the left anterior descending artery (LAD), the right coronary artery (RCA) and the circumflex artery (CX). Moreover, the ratio of intraluminal attenuation (HU) to myocardial attenuation was assessed for all coronary arteries. Clinical data [body mass index (BMI), gender, heart rate] were accessible for all patients.

Mean attenuation (CA) of the coronary arteries was significantly higher for DSCT in comparison to 64- and 16-slice MSCT within the RCA [347 +/- 13 vs. 254 +/- 14 (64-MSCT) vs. 233 +/- 11 (16-MSCT) HU], LM (362 +/- 11/275 +/- 12/262 +/- 9), LAD (332 +/- 17/248 +/- 19/219 +/- 14) and LCX (310 +/- 12/210 +/- 13/221 +/- 10, all p < 0.05), whereas there was no significant difference between DSCT and 64-MSCT for the LV, the Ao and My. Heart rate had a significant impact on CA ratio in 16-slice and 64-slice CT only (p < 0.05). BMI had no impact on the CA ratio in DSCT only (p < 0.001). Improved spatial and temporal resolution of dual-source CT is associated with better opacification of the coronary arteries and a better contrast with the myocardium, which is independent of heart rate. In comparison to MSCT, opacification of the coronary arteries at DSCT is not affected by BMI. The main advantage of DSCT lies with the heart rate independency, which might have a positive impact on the diagnostic accuracy.

Authors: Burgstahler C, Reimann A, Brodoefel H, Daferner U, Herberts T, Tsiflikas I, Thomas C, Drosch T, Schroeder S, Heuschmid M.

Full text: Eur Radiol. 2009 Mar;19(3):584-90. Epub 2008 Oct 25

METHODS
In a larger scale study patients scheduled for conventional coronary angiography (CA) were additionally examined with DSCT. Based on a 13-segment model 30 CT scans of this study population were analyzed for significant stenosis using conventional 3D charts (3D) as well as a specialized cardiac analysis tool (CAT). Diagnostic accuracy and time to diagnosis was recorded for each vessel separately as well as the three readers’ confidence.

RESULTS
With severe coronary artery calcifications, 53 false interpretations of segments were found for the total of 390 coronary segments analyzed. 3D and CAT analysis showed a Sensitivity, Specificity, PPV and NPV of 0.59, 0.91, 0.57, 0.92 and 0.57, 0.92, 0.56, 0.92, respectively. No significant differences in diagnostic accuracy could be found between 3D and CAT (p = 0.1667). 3D took a mean of 5.2 min (3–10 min). With CAT a mean time of 8.2 min (4–12 min) was needed. No significant inter-reader time differences (p = 0.4954) and no significant confidence level differences were found between readers and analyzes.

CONCLUSION
CAT of the coronary tree shows comparable accuracy to manual 3D analysis but needs improvements concerning coronary tree segmentation times.

Authors: Reimann AJ, Tsiflikas I, Brodoefel H, Scheuering M, Rinck D, Kopp AF, Claussen CD, Heuschmid M.
Full text:  Int J Cardiovasc Imaging. 2009; 25: 195-203

Comment: Int J Cardiovasc Imaging. 2009 Feb;25(2):205-8

Methods
Twelve different coronary stents placed in a non-moving cardiac/chest phantom were examined by 128-slice dual-source CT using three CT protocols [high-pitch spiral (HPS), sequential (SEQ) and conventional spiral (SPIR)]. Artificial in-stent lumen narrowing (ALN), visible inner stent area (VIA), artificial in-stent lumen attenuation (ALA) in percent, image noise inside/outside the stent and CTDIvol were measured.

Results
Mean ALN was 46% for HPS, 44% for SEQ and 47% for SPIR without significant difference. Mean VIA was similar with 31% for HPS, 30% for SEQ and 33% for SPIR. Mean ALA was, at 5% for HPS, significantly lower compared with -11% for SPIR (p = 0.024), but not different from SEQ with -1%. Mean image noise was significantly higher for HPS compared with SEQ and SPIR inside and outside the stent (p < 0.001). CTDIvol was lower for HPS (5.17 mGy), compared with SEQ (9.02 mGy) and SPIR (55.97 mGy), respectively.

Conclusion
The HPS mode of 128-slice dual-source CT yields fewer artefacts inside the stent lumen compared with SPIR and SEQ, but image noise is higher. ALN is still too high for routine stent evaluation in clinical practice. Radiation dose of the HPS mode is markedly (less than about tenfold) reduced.

Authors: Wolf F, Leschka S, Loewe C, Homolka P, Plank C, Schernthaner R, Bercaczy D, Goetti R, Lammer J, Friedrich G, Marincek B, Alkadhi H, Feuchtner G.
Full text: Eur Radiol. 2010 Apr 16. [Epub ahead of print]

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

We have the pleasure to welcome Ronald Booij in our Dual Source CT community. He is Radiology technologist at the Erasmus MC in Rotterdam and is in charge of Research an Innovation unit CT.
Read more about Ronald Booij or ask him questions about DSCT.