Coronary CT angiography is an excellent noninvasive imaging modality to visualize stent fractures, even fractures that are not clearly depicted by conventional angiography, according to researchers from South Korea.
They concluded that the improved sensitivity of 64-detector CT enables earlier detection of stent fractures, compared with conventional angiography, thus yielding a higher prevalence of stent fractures and a lower prevalence of in-stent restenosis compared with findings in previous reports.
“However, the versatile image reformation that is possible when viewing curved high-spatial-resolution isotropic MPR images along the long and short axes of the stents also plays an important role,” they wrote in the study published in the December edition of Radiology.
Having three-dimensional data is essential to see stent fractures on CT, particularly the multiplanar reformations (MPRs), co-author Gham Hur, MD, told Cardiovascular Business News. He noted that the advanced visualization techniques do not add any significant time to the diagnosis.
“There are three steps in coronary CTA: acquisition, reconstruction and reformation,” Hur said. “Post-processing, or reformation, is mostly automatic, thanks to the advanced software, but over- and underestimation problems still exist. For manual MPR, such as we use, it takes between 10 and 20 minutes, depending on the degree of motion artifacts.”
Patients were imaged on a Aquilion 64 CT scanner (Toshiba Medical Systems) using the following parameters: a section thickness of 0.5 mm, a pitch of 0.225–0.240, a rotation time of 0.4 second, a field of view of 180 cm, and a tube potential of 120 kV.
Three 0.5-mm-thick axial source images were reconstructed at 0.3-mm intervals and with the data acquisition windows centered at 70 percent, 75 percent and 80 percent of the R-R interval. After the automatic phase-selection software (PhaseXact; Toshiba) became available in September 2007, those phases that involved the least motion were automatically selected.
One to three data sets with the fewest motion artifacts were downloaded onto a three-dimensional workstation (Rapidia, Infinitt) for reformation of two 0.5- and 5.0-mm-thick orthogonal curved MPR images and a varying number of 1.0-mm-thick perpendicular images.
For the study, Han Byeol Lim, MD, and colleagues from the departments of diagnostic radiology and cardiology at Inje University Ilsanpaik Hospital, retrospectively reviewed the CT angiograms of 371 consecutive patients with 545 stents.
They identified 18 fractured stents in 14 patients. Six of these were not detected on conventional angiography at the initial reading.
Researchers also found that six fractured stents showed significant—greater than 50 percent—recurrent in-stent restenosis.
Fractures also were prevalent in overlapping stent placements. Of the 58 arteries with overlapping stent placements, eight had fractures involving 11 stents. Other morphologic factors that may predispose stents to fracture include type (Cypher from Cordis), location (right coronary artery) and extensive length.
“Since the prevalence of coronary heart disease and the use of drug-eluting stents are increasing worldwide, radiologists and cardiologists who interpret coronary CT angiograms obtained in patients with a history of stent implantation should be aware of the findings that suggest fracture,” researchers concluded.
Hur added: “Most fractures so far have been described in conventional angiography, which means many have been missed. Also, indications for catheter angiography are narrower than for CTA. Since CTA is more widely used, it is possible to detect fractures earlier, even before in-stent restenosis occurs.”
Hur said that they currently recommend follow up CT between six months to a year, depending on the degree of associated stenosis,