Hi-Def Detector and 320-row Area Detector CT Open up New Possibilities in Interventional Radiology

I served as a resident at Aichi Cancer Center, where Dr. Yasuaki Arai was playing a leading role in the field of IR in Japan and was engaged in joint research to develop Angio CT with then Toshiba Medical Systems Corporation (now Canon Medical Systems Corporation). In fact, the world's first Angio CT system was installed at Aichi Cancer Center. This novel system featured an Angiography system and a CT scanner which were installed in the same room and shared a single patient couch. I found the Angio CT system to be extremely convenient when I had a chance to actually use it, and it was my belief that such systems would eventually become the clinical mainstream.

In 2003, a long-awaited Angio CT system with a 16-row CT scanner (Aquilion LB) was finally installed at Nara Medical University Hospital. The system was immediately found to be useful for a wide variety of clinical applications. At that time, one of my research interests was the treatment of pancreatic cancer using a method in which anticancer agent is injected directly into the tumor. Pancreatic cancers also tend to have a large number of feeding vessels, and in order to identify the most effective vessel for injecting anticancer agent, it is necessary to introduce a catheter into each individual vessel, obtain contrast CT images, and then check the pattern of contrast enhancement in the tumor to evaluate the drug distribution. We have found Angio CT to be extremely useful for performing these complex procedures.

In 2019, the system was upgraded by installing Alphenix 4D CT with the latest 320-row Area Detector CT (ADCT) scanner, Aquilion ONE. In a later upgrade, a high-definition detector (Hi-Def Detector) was installed.
Alphenix 4D CT is provided with a variety of new functions for improving workflow. One of these new functions, Semi-Auto Registration, allows 3D CT images to be superimposed on Angiography images. Because the Angiography system and the CT scanner share the same patient couch, there is no need to manually adjust the positions of the two images to achieve precise registration. The 3D CT information is used as a roadmap to confirm the locations of devices such as guidewires during the procedure. Auto Table is another useful function that allows the couch position and the C-arm position and angle to be automatically returned to the same settings as before by simply selecting a previously acquired image. This is extremely helpful for cases in which the working angle needs to be changed repeatedly, and we now consider this function to be indispensable in our daily clinical practice.
The SPOT Fluoro dose-reduction function is also very effective. When X-rays are emitted to cover the entire field view, the exposure dose is increased not only for the patient but also for medical staff due to scattered X-rays. When SPOT Fluoro is used, X-rays are limited to the area of interest while retaining the information for surrounding areas. This makes it possible to perform procedures safely with the lowest possible radiation dose (Figure 1).
We have found 320-row CT to be of great value in both vascular and nonvascular IR. For example, in complicated cases, it can be difficult to clearly understand blood flow dynamics during navigation when vascular IR procedures are performed using Angiography alone.
By performing 4D CTA (i.e., ADCT with temporal information), we can precisely visualize very fast blood flow in 3D images that provide stereoscopic views of blood flow dynamics as well as vascular structures. We use this function in many of our cases. For example, in patients with arterial dissection, 4D CTA allows us to assess the blood flow in the true lumen and that in the false lumen even when the blood flow is separated into two layers due to the dissection.

As another example, in patients with arteriovenous malformations, blood flow from the arteries to the veins is extremely fast. It can therefore be difficult to depict the structure of the shunts using Angiography alone. 4D CTA offers very fast scanning speeds, making it possible to obtain a detailed understanding of blood flow dynamics (Figure 2). Challenging cases like these can be diagnosed thanks to 4D CTA. In nonvascular IR, we have found the volume one-shot puncture technique to be particularly effective. When the conventional method is employed, the needle needs to be introduced perpendicular to the CT cross-sectional slice in order to display the entire course of the needle. With ADCT, on the other hand, a total width of up to 16 cm can be scanned at one time, allowing the course of the needle to be displayed even if it is tilted in the craniocaudal direction (Figure 3).

It is my belief that IR is a continually evolving treatment method with a wide range of future applications. For example, transcatheter arterial micro-embolization (TAME) can be performed as a palliative treatment for bone and joint pain. We have treated a few patients with TAME at Nara Medical University and have found it to be quite effective. Symptomatic treatment is also required in oncology, and the importance of not only curative treatment but also palliative care in cancer patients is now widely recognized. The time has come for IR to take on a larger role in the treatment of such patients. One example would be the management of cancer patients with bone metastases. Patients with low back pain or bone pain may benefit from vascular embolization or radiofrequency ablation. Although such treatments do not cure the cancer itself, they will be performed more frequently because they can help to improve the patient's quality of life (QOL).

I was appointed professor in the Department of Diagnostic and Interventional Radiology in February 2022. Looking at the current situation at our hospital, I feel we have established excellent relationships with doctors in other specialties in terms of clinical care. The next step is to elucidate therapeutic approaches whose mechanisms are currently unknown, including basic research, and to develop new treatment methods and medical devices. With regard to more intangible assets, we enjoy strong relationships with our outstanding radiological technologists and nurses. This is essential for the provision of quality care. To take full advantage of the latest Alphenix 4D CT functions described above, we need to work in close collaboration with our radiological technologists. Traditionally, their main role was to operate the equipment and acquire images.

Dr. Toshihiro Tanaka (TT): We've been working together with Canon Medical to conduct joint research in a variety of areas. Embolization Plan was one research project that focused on accurate identification of the feeding vessels of hepatocellular carcinomas. When I heard about the Hi-Def function currently incorporated into the Alphenix 4D CT, I was very much interested and had high expectations for its clinical value.

TT: As I mentioned before, the first thing that comes to mind is coiling, even in the abdomen. Also, pulmonary arteriovenous malformations are considered to have a high recurrence rate. And even when coil embolization is performed properly, they may recur over the long term. To minimize the risk of recurrence, we try to achieve extremely dense coil embolization. Hi-Def allows us to clearly see any gaps between the coils and fill in the gaps completely (Figure 4). In addition, I think it will prove to be extremely useful for tumor embolization and for evaluating the feeding vessels of tumors. Although it's still in the research phase, a new treatment approach using an angiogenesis inhibitor is being developed. The initial findings of this research have shown that the angiogenesis inhibitor can normalize the abnormal cancer vessels, and this method has already been successfully employed in a number of clinical cases. I expect that this will be an area in which high-definition vascular imaging with Hi-Def will prove to be particularly effective.

YH: I really hope you can apply Hi-Def to a wide range of procedures where it's effective.

TT: With a conventional system, we enlarge the field size to a maximum of 6 inches and manipulate the catheter. We've found this to be workable, but when we need to introduce a microcatheter into a smaller vessel, we use Hi-Def 3-inch enlargement. After that, going back to 6 inches is a disappointment. We feel that information is lost at 6 inches because Hi-Def allows us to see extremely minute structures. It's often the case that we notice things we hadn't noticed before. For example, with regard to musculoskeletal pain, we've used Hi-Def to evaluate vessel size in patients with Moyamoya disease, and abnormal vessels measuring 100-200 μm can be clearly depicted. Compared to 6-inch and 8-inch images, Hi-Def 3-inch images clearly show the differences in the blood vessels (Figure 5).

YH: I'm very happy to hear your positive comments. Our goal is to develop and produce equipment that helps you perform your clinical work. First, we want to ensure that the equipment provides the highest quality images. Also, because the equipment uses X-rays, it's essential to minimize radiation exposure to both patients and medical staff. And finally, we want to maximize operability. We plan to make further improvements in all these areas in the future. At the same time, we'd like to further explore the possibility of multi-modality collaboration to better support your clinical needs. Do you have any requests you'd like to share with us today?