A novel Region of Interest (ROI) imaging technique for biplane imaging in interventional suites: high-resolution small field-of-view imaging in the frontal plane and dose-reduced, large field-of-view standard-resolution imaging in the lateral plane

Abstract

Endovascular-Image-Guided-Interventional (EIGI) treatment of neuro-vascular conditions such as aneurysms, stenosed arteries, and vessel thrombosis make use of treatment devices such as stents, coils, and balloons which have very small feature sizes, 10's of microns to a few 100's of microns, and hence demand a high resolution imaging system. The current state-of-the-art flat panel detector (FPD) has about a 200-um pixel size with the Nyquist of 2.5 lp/mm. For higher-resolution imaging a charge-coupled device (CCD) based Micro-Angio -Fluoroscope (MAF-CCD) with a pixel size of 35um (Nyquist of 11 lp/mm) was developed and previously reported. Although the detector addresses the high resolution needs, the Field-Of-View (FOV) is limited to 3.5 cm × 3.5 cm, which is much smaller than current FPDs. During the use of the MAF-CCD for delicate parts of the intervention, it may be desirable to have real-time monitoring outside the MAF FOV with a low dose, and lower, but acceptable, quality image. To address this need, a novel imaging technique for biplane imaging systems has been developed, using an MAF-CCD in the frontal plane and a dose-reduced standard large FOV imager in the lateral plane. The dose reduction is achieved by using a combination of ROI fluoroscopy and spatially different temporal filtering, a technique that has been previously presented. In order to evaluate this technique, a simulation using images acquired during an actual EIGI treatment on a patient, followed by an actual implementation on phantoms is presented.

Figure 1

Schematic of the MAF-CCD detector. The input x-ray photons incident on the CsI phosphor, get converted to light photons. The light photons are amplified by the LII which is coupled to the CCD sensor via a FOT.

Figure 2

Concept of ROI fluoroscopy. The attenuator has differential attenuation regions. For this study a stack of Kodak Lanex screens with a hole in the middle was used as the attenuator.

Figure 3

Image of a head phantom acquired, with the ROI attenuator in the beam.

Figure 4

Processing steps for ROI fluoroscopy images acquired with the attenuator in the beam.

Figure 5

Angiogram of a patient taken with the FPD showing an intracranial aneurysm.

Figure 6

EIGI image acquired using MAF-CCD detector on frontal plane of C-arm.

Figure 7. EIGI image acquired using FPD on lateral plane of C-arm

Figure 8

A functional block diagram showing the different steps involved in generation of ROI fluoroscopy images for simulation.

Figure 9

Different steps involved in the simulation of dose reduction concept on EIGI sequence acquired using the FPD in the lateral C-Arm. The processing demonstrating the steps for ROI fluoroscopy are shown as the interventional sequence is proceeding.

Figure 10. Simulated patient dose reduced EIGI

Figure 11. Bi-plane imaging setup. MAF mounted on the automatic changer on the frontal plane, ROI attenuator mounted on the collimator of the lateral C-arm

Fig 12

Image of the deployed stent obtained using the frontal MAF.

Fig 13

Image of the deployed stent obtained using the frontal FPD for a projection similar to that of the MAF as shown in Fig 12.

Fig 14

Image obtained using FPD in lateral plane. The ring artifact is due to the mask subtraction process used to correct for the brightness mismatch resulting from the ROI attenuator.

Fig 15

DSA Image of an aneurysm model, obtained using the MAF in frontal plane.

Fig 16. Lateral c-arm image of the entire vessel phantom obtained using the FPD with a ROI attenuator. The green circle (diameter approximately the MAF FOV) indicates the region of the phantom imaged by MAF in the frontal plane