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

Dr. Toshihiro Tanaka has taken on many new challenges in expanding the range of clinical applications of interventional radiology (IR), starting from tumor vascular embolisation, to AVM coil embolisation, and then to transcatheter arterial micro-embolisation (TAME) for pain management. He serves as professor of diagnostic and interventional radiology based on his personal philosophy, "Harmony is to be valued." We asked him to discuss the equipment features and functions he has found to be indispensable when performing IR procedures.

Dr. Toshihiro Tanaka,
Professor and Chair, Department of Diagnostic and Interventional Radiology,
Nara Medical University, Nara, Japan

Angio CT simplifies complicated clinical routines

I served as a resident at Aichi Cancre Centre, 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 Centre. 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.

At that time, routine clinical practice at Nara Medical University Hospital was to transfer patients back and forth between the Angiography room and the CT room on stretchers. In patients with liver cancer, Angiography was used to determine the number of tumors and evaluate blood flow dynamics. The patient was first sent to the Angiography room, where catheters were introduced into the superior mesenteric artery and the hepatic artery, and portal venography was performed via the superior mesenteric artery. The patient was then transferred to the CT room, where contrast CT images were acquired via the hepatic artery to visualise the arterial supply. So we made the diagnosis during this phase of the overall process of transarterial chemoembolisation (TACE). After diagnosis, the patient was transferred back to the Angiography room to perform the actual TACE procedure. This clinical routine, in which the patient needed to be transferred between rooms several times, not only placed a severe burden on the patient but also made it difficult to manage the CT room efficiently.
When patients were transferred from the Angiography room, the CT examinations scheduled for all other patients had to be suspended, even when the room was fully booked.

Seamless integration with CT in a wide range of clinical research

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.

4D navigation pioneered by 320-row CT

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 visualise 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).

Future expansion of IR into many new areas

It is my belief that IR is a continually evolving treatment method with a wide range of future applications. For example, transcatheter arterial micro-embolisation (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 recognised. 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 embolisation 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.

But their role has been steadily expanding to include creating the navigation images used for treatment, displaying the images and communicating with the doctors during the procedure, and working together as a team with doctors in treating patients. The doctors operate the catheters during the procedure while constantly communicating with the radiological technologists to set the optimal view angles and navigate to the target vessels.

When visitors from other institutions come to our hospital, they often remark how much they envy us for having such excellent technologists. This is due not only to their outstanding individual skills and capabilities but also, as mentioned before, to the fact that we work in close collaboration, which allows us to inspire each other to achieve even higher levels of professional performance. I place the greatest value on working together as a team and ensuring a positive atmosphere in the workplace.

*Some of the comments and information in this article are the personal opinions and impressions of Dr. Tanaka.

A year in which doctors, technologists, and a manufacturer worked as one team

Dr. Toshihiro Tanaka (TT): We've been working together with Canon Medical to conduct joint research in a variety of areas. Embolisation 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.

Mr. Yoshiyasu Hayashi (YH): We were also very happy when you decided to participate in this joint research because we felt Hi-Def was a very ambitious function and an exciting new challenge. We're very grateful for your participation. Nara Medical University has been taking the lead in IR under the guidance of a number of key opinion leaders (KOLs) in the field, starting with Dr. Tanaka. The university actively participates in international congresses, and we expect that the results of this research will be presented to a global audience. That's the background when we proposed this joint research.

TT: What was the aim of Hi-Def development?

YH: Although some clinical experience had already been gathered for the brain, this was the first attempt to employ Hi-Def in the abdomen. The key advantage of Hi-Def is its extremely small and precise pixel size, which allows the acquired images to be greatly enlarged. To make the best possible use of this advantage, we first needed to develop innovative approaches in all aspects of imaging to fully exploit the performance capabilities of Hi-Def in the abdomen as well.
We developed a dedicated X-ray tube and also optimised image processing techniques to ensure that Hi-Def could perform at its full potential. Our final goal was to ensure that doctors could clearly see the embolic materials, such as coils, as well as minute blood vessels during IR procedures. Various teams in the development department worked closely together to achieve this goal.
Not only the development team but also sales representatives, application specialists, and service engineers were able to receive detailed feedback from doctors, which helped us to improve the quality of Hi-Def when used in the clinical setting. For a full month after system installation, we worked together with the doctors to fine-tune the images and ensure that the system was operating at peak performance.
I'm very pleased and grateful that all the stakeholders were able to work in close collaboration as one team.

TT: Yes, I remember. When I was shown images of cerebral aneurysm coiling in the brain, I expected something like that in the abdomen, and when I actually experienced it in clinical practice, it fully met my expectations. Hi-Def is undoubtedly effective for coil embolisation. One of the unique benefits of Hi-Def is that we can identify the location of the microcatheter in coils. That is, even if a lesion appears to be completely filled with coils, Hi-Def allows us to see any gaps in the coils and identify areas where additional coils can be placed. In addition, when I was studying in Germany, I was involved in research focusing on the embolisation of liver cancers using microspheres, embolic material consisting of tiny spheres with a diameter of only 40 μm. The depiction of minute objects with Hi-Def is an extension of that research, and I have very high hopes for its future development.

YH: Hi-Def has a pixel size 76 μm, and we took on the challenge of applying it to the abdomen after having gained substantial experience in the brain. However, we couldn't apply it to the abdomen in exactly the same way because the abdomen is thicker than the brain. It was very difficult to fine-tune the system and determine the optimal dose settings and image processing parameters. We were finally able to optimize the parameters and achieve the current high level of performance after installation thanks to the suggestions and guidance we received from Dr. Tanaka and the technologists at the hospital.

TT: Yes, parameter setting was difficult at first. To be honest, when I saw it the first time, I had some doubts. I wondered, "Is this going to be usable?" However, we doctors, our technologists, and the staff of Canon Medical worked together as a tight cross-disciplinary team until our efforts paid off. The improvements were remarkable, and I started to have the feeling, "This will really work!"

YH: In what areas do you think Hi-Def can really demonstrate its full potential?

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 embolisation is performed properly, they may recur over the long term. To minimise the risk of recurrence, we try to achieve extremely dense coil embolisation. 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 embolisation and for evaluating the feeding vessels of tumours. 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 normalise the abnormal cancre 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 cathetre. 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 minimise radiation exposure to both patients and medical staff. And finally, we want to maximise 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?

TT: Let me first mention the things I'm really satisfied with. The main thing is the degree of responsiveness. I appreciate your prompt responses and how you carefully consider our requests and try to make improvements. I look forward to working closely with you in the future and developing exciting new technologies. I hope to address not only ease of use in routine clinical practice but also our future visions, including the future evolution of IR, working together with Canon Medical so we can move forward together into a new era.

YH: Thank you very much for taking time from your busy schedule to talk with us today. //

*Some of the comments and information in this article are the personal opinions and impressions of Dr. Tanaka.

* This article was originally published in Alphenix Magazine Vol.3 2022.

Nara Medical University, Nara, Japan

Dr. Tanaka's profile

Dr. Toshihiro Tanaka, professor and chair, Department of Diagnostic and Interventional Radiology, Nara Medical University, Nara, Japan
Specialising in minimally invasive IR treatment of malignant tumors (cancer).
Actively involved in joint research and device development with manufacturers.
Appointed chairman of the Japanese Society of Interventional Radiology in 2020.

Biography
1996: Completed clinical training and graduated from Nara Medical University.
1998: Served as resident at Aichi Cancer Center.
2000: Appointed assistant professor, Department of Radiology, Nara Medical University.
2009: Served as visiting research fellow, Institute of Applied Medical Engineering, Aachen University, Germany.
2010: Named CIRSE Fellow, Department of Radiology, Maastricht University, the Netherlands.
2015: Appointed associate professor, Department of Radiology, Nara Medical University.
2022: Appointed professor and chair, Department of Diagnostic and Interventional Radiology, Nara Medical University.