Using three-dimensional rotational angiography for sizing of covered stents

Assessment of organ and effective dose when using region-of-interest attenuators in cone-beam CT and interventional fluoroscopy

In some medical-imaging procedures using cone-beam CT (CBCT) and fluoroscopy, only the center of the field of view (FOV) may be needed to be visualized with optimal image quality. To reduce the dose to the patient while maintaining visualization of the entire FOV, a Cu attenuator with a circular aperture for the region of interest (ROI) is used. The potential organ and effective dose reductions of ROI imaging when applied to CBCT and interventional fluoroscopic procedures were determined using EGSnrc Monte Carlo code. The Monte Carlo model was first validated by comparing the surface dose distribution in a solid-water block phantom with measurement by Gafchromic film. The dependence of dose reduction on the ROI attenuator thickness, the opening size of the ROI, the axial beam position, and the location of the different organs for both neuro and thoracic imaging was evaluated. The results showed a reduction in most organ doses of 45% to 70% and in effective dose of 46% to 66% compared to the dose in a CBCT scan and in an interventional procedure without the ROI attenuator. This work provides evidence of a substantial reduction of organ and effective doses when using an ROI attenuator during CBCT and fluoroscopic procedures.

Effect of ROI filtering in 3D cone-beam rotational angiography on organ dose and effective dose in cerebral investigations

The assessment of intracranial aneurysms is increasingly performed using three-dimensional cone-beam rotational angiography (3D CBRA). To reduce the dose to the patient during 3D CBRA procedures, filtered region-of-interest imaging (FROI) is presented in literature to be an effective technique as the dose in regions of low interest is reduced, while high image quality is preserved in the ROI. The purpose of this study was to quantify the benefit of FROI imaging during a typical 3D CBRA procedure in a patient's head region. A cone-beam rotational angiography unit (Infinix) was modeled in GMctdospp, an EGSnrc-based Monte Carlo software, which calculates patient dose distributions in rotational computed tomography. Kodak Lanex, a gadolinium compound, was chosen to be the ROI filter material. The adult female ICRP reference phantom was integrated in GMctdospp to calculate organ and effective doses in simulations of FROI-CBRA examinations. During the Monte Carlo simulations, different parameters as the ROI filter thickness, the ROI opening size, the tube voltage, and the isocenter position were varied. The results showed that the reduction in dose clearly depends on these parameters. Comparing the reduction in organ dose in standard 3D CBRA and FROI-CBRA, a maximum reduction of about 60%-80% could be achieved with a small sized ROI filter and about 40%-70% of the dose could be saved using a ROI filter with a large opening. Further we could show that dose reduction strongly depends on filter thickness, the location of the organ in the radiated area, and the position of the isocenter. As a consequence, dose reduction partially differs from theoretically calculated values by a factor up to 1.6. The effective dose could be reduced to a minimum of about 40%. Due to the fact that standard 3D CBRA is only used for the assessment of aneurysms at present and, thus, most of the patient dose originates from the aneurysm treatment (with 2D techniques) itself, the dose reduction effect of ROI filtering in 3D CBRA tends to be much smaller, if the patient dose of a whole aneurysm treatment procedure is considered.

Update on New Tools for Three-dimensional Navigation in Endovascular Procedures

Three-dimensional (3D) guidance for endovascular procedures has developed over the last decade from 3D rotational angiography to the use of dynamic 3D roadmap techniques. The latest development is image merging. This technique combines real-time feedback of fluoroscopy with optimal soft-tissue contrast of previously performed computed tomography (CT) or magnetic resonance angiography. Merging of CT angiography and cone-beam CT/fluoroscopic images is feasible, and preliminary results look promising. Merging will allow us to further reduce radiation exposure, contrast dose, and procedural time, and its main use and benefit will be in complex endovascular interventions.

Imaging of the thoracic aorta

Three-dimensional vascular imaging techniques offer a significant advantage over traditional imaging techniques. Spatial resolution of current state-of-the-art allows sufficient depiction of anatomical detail. Pre-operative planning of complex endovascular procedures is facilitated by state-of-the-art imaging. Cone-beam CT holds great promise in guiding complex endovascular procedures.

Diagnosis of unruptured intracranial aneurysms: 3T MR angiography versus 64-channel multi-detector row CT angiography

BACKGROUND AND PURPOSE

We compared 3-dimensional time-of-flight magnetic resonance angiography (3D TOF MRA) using a 3-tesla (T) MR unit with 64-channel multi-detector row computed tomographic angiography (64-MDCTA) for detection and characterization of angiographically proven unruptured intracranial aneurysms.

METHODS

Thirty-eight patients with 47 aneurysms and 8 patients without aneurysms underwent 3T, 3D TOF MRA; 64-MDCTA; and intra-arterial angiography. As a first study, 3 radiologists blinded to pertinent clinical information independently reviewed MRA and CTA images. We evaluated diagnostic accuracy using an alternative free-response receiver operating characteristic (AFROC) analysis and evaluated the sensitivity and specificity of each technique. Next, 2 radiologists used volume-rendering images generated from MRA or CTA data to evaluate the morphology of the 47 aneurysms detected, and MRA and CTA results were compared. Three-dimensional digital angiography (DA) images were used as the standard of reference.

RESULTS

On the AFROC analysis, the value of the mean area under the AFROC curve (A(1)) was 0.91 for both modalities. Mean sensitivity of 89% and specificity of 76% for MRA were not significantly different from sensitivity of 87% and specificity of 79% for CTA. Therefore, when used to evaluate aneurysmal morphology, both modalities appear satisfactory for determining these vascular anomalies.

CONCLUSION

Three-tesla, 3D TOF MRA and 64-MDCTA are excellent modalities with high diagnostic accuracy for evaluating unruptured intracranial aneurysms and no significant difference between them in diagnostic performance.

[Three-dimensional renal angiography]

The usefulness of three-dimensional angiography is not fully established except for neurovascular diseases. We report a case of significant renal artery stenosis not shown on conventional angiography because of its orientation along the axial plane, where 3D imaging allowed complete analysis of the lesion leading to endovascular treatment.

Endoluminal AAA repair using intravascular ultrasound for graft planning and deployment: a 2-year community-based experience

PURPOSE

To examine the effectiveness of intravascular ultrasound (IVUS) and digital subtraction angiography (DSA) for preoperative planning and intraoperative deployment of stent-grafts to treat abdominal aortic aneurysms.

METHODS

One hundred seventy patients (143 men; mean age 73.6+/-7.2 years, range 51-89) underwent successful DSA and IVUS to determine suitability for stent-graft repair. Patients subsequently received the AneuRx (n=157) or Ancure (n=13) device; intraprocedural IVUS was used to survey the proximal endograft for proper apposition to the aortic wall.

RESULTS

Reliable preoperative IVUS measurements were obtained in all patients. Plaque morphology was assessed in 140 (82.3%) aortic necks; in 36 (25.7%), preoperative IVUS showed high-grade atherosclerotic plaque in the nonaneurysmal abdominal aortic neck. The procedure was successful in 168 (98.8%) cases (1 [0.6%] acute conversion and 1 access failure). There were 2 (1.2%) periprocedural deaths related to bowel ischemia. Four (2.3%) patients developed graft occlusion/kinking and 2 (1.2%) developed renal failure requiring dialysis within 30 days. Multivariate logistic regression analysis revealed that female gender (p=0.0247), a short nonaneurysmal aortic neck (p=0.0185), and presence of high-grade atherosclerotic plaque (p=0.0185) correlated with major acute complications. Over a mean 10.4-month follow-up (range 1-25), 11 patients died of unrelated causes; there was no known AAA rupture or device failure. The Kaplan-Meier estimate of survival at 1 year was 91.0%+/-2.8%. Sixteen (9.4%) patients underwent 17 secondary procedures for endoleak or graft limb occlusion at a mean 5.4 months after stent-graft repair (freedom from secondary intervention at 1 year 86.5%+/-3.2%).

CONCLUSIONS

Our findings suggest that IVUS may identify patients at increased risk of major adverse complications following endovascular repair. The combination of IVUS and DSA for endoluminal stent-graft planning and placement provides excellent short- and mid-term patient outcomes.

Three-dimensional rotational angiography in peripheral endovascular interventions

PURPOSE

To demonstrate the feasibility and applicability of 3-dimensional rotational angiography (3D-RA) in the assessment of candidates for endovascular treatment of occlusive or aneurysmal arterial disease.

TECHNIQUE

In 3D-RA, a continuous rotation of the fluoroscopic tube around the region of interest is made while intra-arterial contrast is continuously infused. The area of interest is placed in the isocenter in both frontal and lateral planes. Images are acquired at a rate of 12.5 frames per second at a rotation speed of 30 degrees per second. Injection protocols are adjusted according to the anatomical location. The acquisition takes 8 seconds and yields 100 contrast-enhanced cinefluoroscopic images that are automatically reconstructed within 5 minutes to yield a 3D volume that can be rotated and viewed in any direction. Measuring the diameter of the target vessel and length of the lesion can be performed in the same session. An initial evaluation of this technique in 101 patients with known peripheral vascular disease yielded diagnostically adequate images preprocedurally while adding a maximum of only 10 minutes to the endovascular procedure: 5 minutes for reconstruction and another 2 to 5 minutes for measurements, which were made without difficulty in all cases. 3D-RA aided in selection of the optimal fluoroscopic tube angulation for the endovascular procedures and provided assessment of the interventional results comparable to angiography.

CONCLUSIONS

Our preliminary experience suggests that 3D-RA appears to be a valid tool in the pre- and periprocedural assessment of patients treated endovascularly for both aneurysmal and occlusive peripheral arterial diseases.

3D rotational angiography of transplanted kidneys

PURPOSE

To develop a protocol for 3D rotational angiography (3D-RA) of the transplant renal artery.

MATERIAL AND METHODS

3D-RA was consecutively performed in 39 renal transplanted patients with suspicion of renal artery stenosis. A series of images were acquired while the C-arm of the equipment rotated around the region of interest. Contrast media in different concentrations were given through a 1.4 mm catheter with different sites of injection in the ipsilateral iliac artery. The 3D reconstructions were done at a workstation. Suspected stenoses were in most cases verified with pressure measurement, and a systolic pressure gradient of 10 mm Hg or more was regarded as significant.

RESULTS

28 stenoses were found in 24/39 patients (62%); 21/28 (75%) were verified by pressure measurement. The 3D reconstructions gave a better description of the stenoses in 10 patients.

CONCLUSION

3D-RA is a helpful supplement in cases with complicated vascular anatomy, especially when intervention may be indicated. The best results were achieved with the catheter tip in the proximal iliac artery and 70-75 ml of a high concentration contrast medium at a flow rate of 8-10 ml/s.