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]

We sought to determine the agreement for the quantification of cardiac chamber dimensions, volumes, and myocardial mass between dual-source computed tomography (DSCT) and echocardiography.

Material and methods

One-hundred patients underwent DSCT and transthoracal echocardiography within 1 week. Measurements of dimensions were obtained in standardized planes in end-systole and end-diastole and included the anterior-posterior diameter of the left atrium, septal and posterior wall thickness, and inner diameter of the left ventricle. Global left ventricular (LV) functional parameters [end-systolic volume (ESV), end-diastolic volume (EDV), ejection fraction, and LV myocardial mass (LVMM)] were computed using semiautomated software. ESV, EDV, and LVMM were normalized to the body-surface-area (BSA). Intraobserver and interobserver agreement of DSCT analysis was assessed. Correlation between DSCT and echocardiography was tested through linear regression and Bland-Altman analysis.

Results

DSCT measurements had an excellent inter- and intraobserver agreement with close limits of agreement (R = 0.85-0.99, P < 0.001). All measurements obtained with DSCT showed a significant correlation with echocardiography, with close limits of agreement between modalities for all parameters. Significant differences of the mean difference from zero were only found for septal and posterior wall thickness (P < 0.001) (with a homogenous underestimation) and for EDV/BSA (P < 0.05) (showing an overestimation) in DSCT compared with echocardiography. No significant directional measurement bias was found for any parameter except for LVMM/BSA (R = 0.24, P < 0.05).

Conclusion

Our results indicate that DSCT provides reliable measurements of LV dimensions, volumes, and myocardial mass with similar values as compared with echocardiography.

Authors

Stolzmann P, Scheffel H, Trindade PT, Plass AR, Husmann L, Leschka S, Genoni M, Marincek B, Kaufmann PA, Alkadhi H.
Full text: Invest Radiol. 2008 May;43(5):284-9.

Materials and methods: Sixty-two patients were included for neck imaging with DSCT. MPRs from an axial dataset and an additional short spiral parallel to the mouth floor were acquired. Leading anatomical structures were then evaluated with respect to the extent to which they were affected by dental artifacts using a visual scale, ranging from 1 (least artifacts) to 4 (most artifacts).

Results: In MPR, 87.1 % of anatomical structures had significant artifacts (3.12 +/- 0.86), while in angulated slices leading anatomical structures of the oropharynx showed negligible artifacts (1.28 +/- 0.46). The diagnostic growth due to primarily angulated slices concerning artifact severity was significant (p < 0.01).

Conclusion: MPRs are not capable of reducing dental artifacts sufficiently. In patients with dental artifacts overlying the anatomical structures of the oropharynx, an additional short angulated spiral parallel to the floor of the mouth is recommended and should be applied for daily routine. As a result of the static gantry design of DSCT, the use of a flexible head holder is essential.

Authors: Ketelsen D, Werner MK, Thomas C, Tsiflikas I, Koitschev A, Reimann A, Claussen CD, Heuschmid M.

Full text: Rofo. 2009; 181: 54-9

Full text: Eur Radiol. 2009 Feb 4.

Authors:
Paul Stolzmann, Joseph Knight, Lotus Desbiolles, Willibald Maier, Hans Scheffel, André Plass, Vartan Kurtcuoglu, Sebastian Leschka, Dimos Poulikakos, Borut Marincek, Hatem Alkadhi