The value of dual-energy bone removal in maximum intensity projections of lower extremity CT angiography
OBJECTIVE
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
In my experience bone extraction of distal third tibia is poor with both DEBR or manually. how do you deal with it. please guide for the same
Dear Dr. Mahshwari,
thanks for your question. Indeed, the extremely narrow residual lumen in distal crural arteries can pose a challenge for DEBR if these are very dense calcified plaques, especially in severe smokers’ PAOD. As the individual voxel in the image dataset mostly contains more calcium than iodine, DEBR has physically no chance to provide an accurate depiction of the residual patent lumen.
We deal with this in the first place by using a rather long injection scheme and scanning rather late in order to avoid overtaking the bolus. In cases of critical ischemia, we additionally perform a dynamic multi-phase acquisition (‘adaptive 4D spiral’) with a small, short contrast bolus. Then, we see the bolus passing through the arteries, making it possible to differentiate patent and occluded vessels even in very small residual diameters in presence of dense circular calcified plaques. Like that, we have the complete information about large and small arteries, about bypass patency, about plaque distribution and composition, and about perfusion dynamics and severe ischemia. As renal insufficiency is also extremely common in these patients, we sometimes only acquire this latter dynamic dataset with only 40 ml of contrast material, just to clarify whether there is any residual blood supply or not.
Kind regards,
Thorsten Johnson