Dr. Siegel is System Chief, Interventional Radiology
Services, North Shore LIJ Health System, and Associate Professor of
Radiology, Hofstra North Shore LIJ School of Medicine, New Hyde Park,
NY.
Interventional radiology has evolved rapidly over the
last two to three decades, primarily due to refinements in catheters and
catheter-based devices. These technological advances have allowed for
the development of new techniques and applications of interventional
therapy in territories previously not reachable. While image quality has
improved and digital technology has been used to its full advantage
over time in the evolution of angiography and interventional radiology
suites, until recently little had really changed with respect to the way
imaging has been utilized to guide these interventional procedures.
Cone-beam
computed tomography (CT), developed several years ago, has
revolutionized the way we guide procedures by allowing for soft-tissue
imaging in the angiography suite that can be used with fluoroscopy.
While rotating C-arms and 3-dimensional (3D) acquisition techniques were
developed nearly 20 years ago, current technology adds the ability to
image soft tissue with CT, along with improvements in fluoroscopic and
angiographic imaging of contrast-filled vessels and other structures.
Techniques for software reconstruction, manipulation, and analysis
continue to be refined, and they now aid the interventional radiologist
in guiding both vascular and nonvascular procedures in ways unimaginable
as recently as 5 to 7 years ago.
At the forefront of the
development of this technology is Philips Healthcare, whose flagship
interventional suite is the Allura Xper FD 20 system. Besides providing
the high-quality fluoroscopy and digital x-ray acquisition systems now
customary in modern interventional suites, the ceilingsuspended C-arm of
the Allura Xper FD 20 system can perform high-speed rotational scanning
with or without simultaneous contrast injection, depending on the
situation. This digital image dataset is then processed in seconds;
depending on the technique utilized, the dataset provides
interventionalists with a 3D vascular or soft-tissue image for diagnosis
and 3D road mapping. Using the dedicated XperGuide software, this
dataset also can be used to guide percutaneous interventions with the
aid of interactive needle-path planning and guidance software. This
sophisticated software overlays a preplanned needle path, which the
operator designs at an integrated workstation. Previously acquired CT
scans and images from other modalities, such as magnetic resonance
imaging (MRI) and MR angiography, can also be imported and superimposed
on a fluoroscopic image.
This article reviews the different
abilities of the 3D tools available in newer interventional suites and
provides an overview of their various clinical applications.
3D rotational angiography and road mapping
Rotational angiography takes advantage of the C-arm’s ability to
rotate rapidly around the patient and acquire angiographic images at
numerous oblique projections around its arch. Contrast injection volume
and duration must be coordinated with the rotation speed and the desired
images. Angiographers understand that the ability to see a vessel’s
origination or the exact point and angle of branching is essential to
planning procedures that require selective catheterization and precise
endovascular therapy. The 3D reconstructed angiogram can also be used
for 3D road mapping. The 3D image can be superimposed on the live
fluoroscopic image and manipulated together with the live fluoroscopic
image. Oblique angles can be obtained, the patient can be moved, and the
image can be magnified during endovascular manipulations and
interventions. Previously, numerous stationary oblique “runs” were
required, using trial and error; once the appropriate projection was
determined, it was then employed for treatment planning and guidance.
With
practice, interventionalists gain an understanding of when the added
time, contrast, and radiation of these rotational acquisitions will
ultimately lead to lower cumulative procedural time, contrast use, and
exposure.
Cone-beam CT
Cone-beam CT employs image
acquisition similar to that of rotational angiography. Computer software
then performs a sophisticated 3D reconstruction, resulting in images
that can be viewed as a multiplanar reconstruction. These images can be
manipulated, rotated and zoomed; adjustments in window and level also
can be made. Imaging soft tissue simultaneously with opacified vessels
can be essential to appreciating the relationship of these structures
and understanding the blood supply and drainage of various organs. In
interventional oncological procedures, when caustic chemotherapeutic
preparations or radioactive particles are to be introduced into the
liver vessels, confining the materials within the liver is essential, as
non-target embolization can be catastrophic, especially when it
involves the GI tract. If a vessel is opacified during such a procedure
and its vascular territory is uncertain, XperCT can be performed during
contrast injection, and the vascular distribution identified on that
soft-tissue imaging. These techniques can be utilized outside the liver,
as well. We often utilize cone-beam CT before embolization to evaluate
the potential distribution of the embolic. Following embolization
procedures, XperCT can assess the precise territory embolized, making it
clear whether further embolization is necessary.1
Understanding
the relationship of vessels to surrounding structures can be essential
to diagnosing different vascular conditions. Paget-Schroetter syndrome,
or thoracic outlet syndrome, is a condition where the subclavian vessels
are crushed between the first rib and the clavicle and confined by the
scalene muscles between those bony structures. This generally occurs
when the affected arm is abducted and extended. Figure 1 is a cone-beam
CT image that demonstrates Paget-Schroetter syndrome. On this image,
compression of the subclavian artery by the surrounding structures is
beautifully depicted.
XperCT can also be employed during
interventional procedures to locate and evaluate devices. We have used
cone-beam CT imaging to guide filter placement in patients with severe
contrast allergies or renal failure, to guide fenestration of aortic
dissections by locating the appropriate point for flap puncture, and to
evaluate the course of catheters or guide wires when it is unclear if
the true lumen of an occluded vessel was traversed or if a collateral
vessel that would be dangerous to dilate was catheterized. The
applications for this technology continue to expand.
Interventional tools for needle guidance
The 3D image dataset obtained by the cone-beam CT acquisition of the
Philips FD20 Allura Xper unit can be used with the dedicated needle-
guidance software to plan a needle path and then to aid the operator in
precisely placing the needle during a variety of interventional
procedures. The 3D CT image is first used to design the course of a
needle or multiple needles that do not traverse any significant vascular
or other dangerous structures. The unit will then assume the necessary
compound oblique positions based on calculated coordinates. Initially,
the C-arm will assume a “down the barrel” projection, or target view,
and superimpose a circle on the fluoroscopic field where the needle
should be placed. After fluoroscopically guided placement of the needle,
so that only a point is seen, the C-arm is then turned to an orthogonal
view to monitor progress of the advancing needle. When the unit is
turned to this orthogonal view, or to any position, the 3D soft-tissue
image and needle path remain superimposed on the fluoroscopic image.
Biopsies and other procedures requiring needle access can be performed
more accurately and reliably, translating into fewer needle passes and
lower complication rates, especially when related to bleeding and
post-procedure discomfort. Figure 2 is a target view for a biopsy of a
19-year-old man with a benign cartilaginous lesion of the iliac bone. Radiation dose
Radiation
exposure to the patient is certainly a factor in deciding how and when
cone-beam CT and/or 3D angiography should be utilized in interventional
practice. While rotational C-arm imaging techniques certainly deliver a
greater radiation dose to the patient than does conventional
fluoroscopy, in many situations, this technology can actually
dramatically decrease the total fluoroscopy time and number of
individual digital acquisitions—therefore decreasing overall radiation
exposure.
When a needle can be advanced under real-time
fluoroscopic guidance after a single cone-beam CT acquisition, the need
for interval CT scanning during manipulations and needle passes is
eliminated. Even with the addition of an extra CT scan to confirm needle
position, cumulative radiation dose to a patient during a complex
biopsy or other procedure requiring CT guidance is usually decreased.
For these situations, the Philips Allura Xper FD20 system allows for a
lower-dose cone-beam CT acquisition. This will produce an image of
somewhat lower quality, but it can be used to determine needle position
accurately. The overall decrease in radiation to patients during biopsy
procedures has been validated in several published studies.2
Complex interventional procedures
We
now use XperGuide in many clinical situations where accurate CT-needle
guidance placement is needed in conjunction with additional vascular or
nonvascular catheter and guide wire-based procedures. The combination of
soft-tissue CT imaging, needle-guidance software, and 3D angiographic
imaging can often simplify what would be relatively complex or
cumbersome procedures; at times, it eliminates the need to move a
patient from one suite to another where these different modalities are
available. There are several reports of translumbar endoleak
embolization utilizing cone-beam CT guidance for sac puncture.3 Figure 3 demonstrates an example of XperCT following endoleak embolization using coils, a vascular plug, and tissue acrylic.
We
regularly perform nephrostomy placement, biliary drainage, and complex
fluid collection drainage with Xper guide. Needle placement can be
guided with the accuracy of CT imaging in an environment where
subsequent catheter manipulations and exchanges can be performed with
high-quality fluoroscopic guidance. Needle guidance has significantly
expanded our interventional armamentarium. For example, we have
performed puncture and intubation of the pancreatic duct for stenting of
a persistent leak. Utilizing overlay of an MR image for targeting the
cisterna chili, we were able to access the thoracic duct and then
embolize a postoperative leak. Figure 4 demonstrates an intraprocedural
XperCT with MR overlay, obtained in a patient with a venous malformation
where recurrent symptoms were related to a deeper, previously untreated
loculation. This deeper portion of the malformation was targeted and
successfully treated with sclerotherapy, resulting in complete symptom
relief.
Conclusion
The availability of 3D
angiographic and CT imaging with needle-guidance software in the
traditional interventional environment brings us one step closer to the
full-service, image-guided procedure suite, where interventional
radiologists can perform all procedures with the required technology at
their disposal. Future developments in this technology should continue
to enhance our precision and expand the role of interventional medicine.
Acknowledgement: The author would like to thank his
colleague, Igor Lobko, MD, for his collaboration in much of the work
discussed in this article.
References
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al. Utility of C-arm CT in patients with hepatocellular carcinoma
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Sicco J, Strijen van Marco JL, Es van Hendrik W, et al. Effective dose
during needle interventions: Cone-beam CT guidance compared with
conventional CT guidance. J Vasc Interv Radiol. 2011;22:455-461.
- Bindsbergen
van Lars, Braak Sicco J, Strijen van Marco JL, de Vries Jean-Paul PM.
Type II endoleak embolization after endovascular abdominal aortic
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