3-D Rotational Angiography in the Cardiac Cath Lab
Advanced imaging modalities are accelerating the knowledge and understanding of cardiovascular diseases at a rapid rate, and new imaging modalities are no longer in the domain of the noninvasive cardiologist, as these new techniques also apply to imaging in the cardiac catheterization laboratory.
In particular, 3-dimensional (3-D) rotational angio-graphy is a novel and exciting modality finding rapid application in the catheterization laboratory. This article reviews the basics of 3-D rotational angiography, methods of image acquisition, 3-D image reconstruction and then looks into early results of the technique.
Basics of Rotational Angiography
Traditional diagnostic coronary angiography is performed over 1.1 million times per year in the United States.1 Technical improvements have been limited to methods of image acquisition and display, and the procedure has remained fundamentally unchanged since Mason Sones selectively injected a coronary artery in the late 1950s.2 It is now clear from studies using intravascular ultrasound,3 infrared spectroscopy,4 fractional flow reserve5,6 and noninvasive coronary computed tomography studies,7,8 that coronary artery disease and its therapy are more complex than what is shown by traditional angiographic 2D projection lumenography.
Rotational angiography is based on tomographic (3-D) reconstruction of cath lab-acquired images. It was first described in 19989 and sought to increase diagnostic accuracy over standard, fixed-view angiography with the additional benefits of reducing contrast and radiation dose. This technique avoids gaps in information that arise from deviation in angles of orthogonal views as typically occur during sequential, fixed-view invasive angiography. With the resultant increase in information available to the operator, the final interpretation of the angiogram is more optimal to assess the severity of coronary lesions and to better understand the 3-dimensionality of coronary artery size, stenosis and spatial course.
The premise of rotational angiography is to obtain all projections of each coronary artery system in a single, longer injection of contrast in one cine angiogram acquisition using 3-D volumetric reconstruction of angiographic images.
Rotational Angiography Methods
Image acquisition in rotational angiography is initially the same as conventional coronary angiography. The patient is prepared in sterile fashion in the angiography suite and standard coronary diagnostic catheters are placed into the coronary artery of interest after routine arterial access. The region of interest is centered on the rotational axis to ensure complete acquisition during the entire rotation. With the C-arm in the posterior-anterior position, the heart is centered under fluoroscopy. With the C-arm in the lateral position, the table height is adjusted, again using fluoroscopy to center the heart. The table position and height should not be adjusted after this point. After centering the region of interest, the C-arm start and stop positions must be determined. The C-arm is positioned manually at the starting and ending positions and confirmed on the acquisition console sequentially. Once these positions are confirmed, images are acquired by depressing the acquisition switch. The gantry rotates about the patient, during which time the patient must remain immobile and must hold his/her breath to assure as motionless a state as possible (Figure 1).
The duration of each image acquisition run is determined by the amount of C-arm rotation desired by the operator and affects the overall dose of radiation and contrast administered to the patient. As some C-arm systems can move at a maximum rate of 30–55 degrees per second, the time required to swing through the entire 180-degree arc of rotation varies from 3–6 seconds. It may take up to 2 additional seconds at the beginning of the rotation for the C-arm to reach that maximum speed and 2 more seconds at the end of the rotation to slow the C-arm down. Since a full 180-degree rotation can take up to 10 seconds, this technique mandates the use of a power injection system. Early safety concerns of prolonged coronary injections have faded with experience, as shown by Garcia et al, who published clinical safety and feasibility of long injections in a 30-patient cohort.10
If a standard vascular power injection system is used, the contrast injection rate and total volume should ensure complete filling of the coronary artery during image acquisition. Contrast injection can be delayed by 1 second as the C-arm ramps up to speed, which ensures complete filling by the time full speed is achieved. If a dedicated coronary injection system is used, contrast flow rate and volume can be adjusted semimanually up to preprogrammed maximums determined by the operator. Contrast dose may vary from 14–22 mL and 14–30 mL for the left and right coronary arteries, respectively.10
3-D Reconstruction of Rotational Angiographic Images
After the acquisition, 120 contrast images are transferred to a computer workstation. Around the isocenter of rotation, a predefined default volume is automatically reconstructed as a 3-D volume much the same as the volumes obtained by cardiac CTA. The reconstructed volume can be viewed interactively with real-time volume rendering, using the same techniques at CTA analysis.11
Each 3-D reconstruction image contains small 3-D cubic data referred to as “voxels” (the 3-D equivalent of a pixel). Three possible resolutions for reconstruction are typically available for volume data, corresponding to the number of voxels along each 3-D axis (x, y, z). These resolutions are 1283, 2563 and 5123. Each doubling of resolution results in an 8-fold volume voxel increase (= 2 x 2 x 2).12 The 3-D volume images are rendered for 3-D display after reconstruction.
Real-World Experience with 3-D Rotational Angiography
3-D rotational angiography may be applied to many clinical problems and questions that include neurointervention and abdominal aortic pathology. This article will review cardiac applications that include coronary arteries (anatomy, course, stenosis, congenital anomalies16) and non-coronary cardiac evaluations that also include the cardiac veins13 and the coronary sinus14,15 as well as in congenital anomalies.
A driving component behind the adoption of 3-D rotational angiography was the ability to limit radiation and contrast exposure. Patients with severe chronic kidney disease were a group that was examined early with this technology. Kuon et al reported excellent image quality and significantly lower contrast doses in renal patients using a gantry rotation of 40 degrees/second and an angle of 120 degrees. The volume of contrast used was 60% lower in the rotational angiography group versus the standard angiography group.17
Similarly, optimizing views to limit error and improve ease of use without sacrificing image quality is key. One step in enhancing ease of use involves automated (computer-based) choosing optimal cardiac phases. Rasche et al described an automated approach in a porcine model where 4D data sets of the region of interest were reconstructed at low spatial resolution. An image quality index first quantified the image quality using just one 3-D volume. The optimal parameters were then applied to 16 data sets from 8 pigs that found a high correlation (> 84%) for high-quality images.18
Optimal coronary artery visualization in three dimensions is achieved by creating models from orthogonal 2D images of the coronary tree, allowing patient-specific optimal viewing maps that limit both vessel foreshortening and overlap. The development and feasibility of this technique was recently shown in a group of 137 patients.19 More recently, Neubauer and colleagues presented 23 patients who underwent rotational angiography with a 7.2-second injection during a 180° rotational run. Image processing was fully automatic, consisting of least motion cardiac phase determination, gated iterative reconstruction and 2D motion compensation within the gating window. No adverse events occurred in these patients, and the rotational images allowed more segments to be visualized in 85% of patients compared with the 2D data, proving the feasibility of fully automated image processing.20 Figure 2 shows the detail and accuracy of 3-D reconstruction compared to conventional angiography.
The most important question regarding the future of 3-D rotational angiography is simply: Is it better than traditional standard angiography, and does it enhance cath lab data? Two studies published in 2008 reviewed these questions. Agostoni and colleagues evaluated quantitative coronary angiography in the “working-view” standard angiographic views with automatically generated 3-D reconstructed views in 36 patients undergoing PCI with a marked guidewire used as the gold-standard reference. Eighty-one segments from the 36 patients were evaluated (12 left anterior descending arteries, 12 left circumflex arteries, 12 right coronary arteries [RCA]), and 3-D reconstruction was feasible in all segments. The correlation between the 3-D segment length and the marker guidewire showed the best agreement, with segment lengths on average 2.3 mm longer on 3-D reconstruction than standard angiography. This significantly improved length measurements over standard angiography, though reference vessel diameter was not different between the groups.21
A second study compared quantitative coronary analysis of standard angiography with 3-D rotational angiography in 100 patients by independent blinded review. Although no difference was seen in the total number of lesions recognized and clinical decisions were not changed, rotational angiography showed superior visualization of several vessel segment (the diagonals, distal RCA, posterolateral and posterior descending branches) over standard angiography. Importantly, contrast volume, radiation exposure, and image acquisition time were all significantly lowered in the rotational angiography group compared to standard angiography.22
3-D rotational angiography is a novel technique that brings 3-D images to the cardiac cath lab. It entails gantry rotation, acquiring sequential projection images from multiple angles and reconstructing them into 3-D data sets very similar to those obtained by cardiac CTA.
3-D rotational angiography has yet to prove its benefit. Experience is growing, and many invasive cardiologists are exploring its applications as systems become more widely available on the commercial market. While 3-dimensionality has intuitive benefits, such efficacy is unproven. Lowering patient contrast and radiation exposure are apparently clearcut benefits, making a strong case for safety in obtaining high-quality images with more data than traditional 2D angiography. As more cardiologists gain experience in this modality, its true application will become clear for clinical use.
From the *Minneapolis Heart Institute Foundation, Minneapolis, Minnesota and the †University of Minnesota Cardiovascular Disease Division, Minneapolis, Minnesota.
The authors report no conflicts of interest regarding the content herein.
Manuscript submitted May 18, 2009 and final version accepted June 8, 2009.
Address for correspondence: Robert S. Schwartz, MD, FACC, Minneapolis Heart Institute Foundation, 920 E. 28th Street, Minneapolis, MN 55414. E-mail: email@example.com
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