https://orcid.org/0000-0001-7979-6803
Abstract
We herein report the first use, to our knowledge, of computed tomography-ultrasound (US) fusion technique to follow-up Crohn’s disease complications. This novel technique employs real-time reconstructed fusion of previously obtained tomographic images onto the US image software, allowing accurate bedside spatial resolution, localization, and lesion characterization by US.
Introduction
Abdominal imaging has a crucial role in Crohn’s disease (CD) diagnosis and management.1, 2 Although guidelines favor the use of non-radiating imaging techniques, computed tomography (CT) is still often used, mainly in acute settings of suspected CD complications. The use of CT carries a high risk of radiation exposure, mainly if repeated exams are warranted. An imaging modality that permits repeated and precise imaging without radiation is required. Real-time integration and reconstruction of previously performed CT studies with ultrasound images (US-CT fusion) has recently emerged as a novel technology integrated in high-end modern US machines.3 It comprises a field generator emitting a weak magnetic field, which creates the tracking volume. The system is then able to track the location of the US transducers when they are placed inside the tracking volume by inducing a small current in the sensor coils that are embedded in the transducers. The system enables correlation of different scan sets by performing spatial mapping from distinct image spaces. US-CT fusion allows widening the limited acoustic window of US by the extended view field of CT and increasing the spatial resolution by use of US.4
We herein report our first proof-of-concept experience with 4 CD patients in the use of fusion of real-time bowel US with CT scan images performed for the follow-up of CD and its complications.
Case Reports
CT scans were performed on a Philips scanner. US-CT fusion was performed using a Philips Epiq 7G with an electromagnetic transmitter and electromagnetic sensors on the US probe. Matching (co-registration) of the CT and US datasets was performed using the aortic bifurcation, which is an easily defined anatomical landmark. Phillps-PercuNav system was used for transforming the CT images into dynamic representations fused with US.
Patient 1: A 20-year-old previously healthy male was admitted due to severe abdominal pain and fever (38.5 °C). Abdominal CT demonstrated increased bowel thickness of the distal and terminal ileum and an inflammatory mass measuring 3 cm in the right pelvis. A partial response to antibiotic therapy prompted a loco-directed US fusion study that did not demonstrate a reduction in the size of the inflammatory mass. The antibiotic treatment regimen was changed, resulting in significant clinical improvement. Two weeks later, the patient was readmitted due to recurrence of right abdominal pain. Repeated fusion study demonstrated enlargement of the same inflammatory mass to a diameter of 4 cm with demonstration of gas bubbles (Figure 1A). Antibiotic treatment was restarted, with little improvement. Repeat fusion study did not demonstrate any improvement. A repeat abdominal CT confirmed the fused imaging findings. The patient underwent laparoscopic resection of the terminal ileum and cecum and made uneventful recovery. The histology specimen confirmed the diagnosis of CD.
Computed tomography-ultrasound (CT-US) fusion images. Abbreviations: CT, the CT image; Fusion, the fused image; Transducer, spatial location of the US transducer; US, real-time US image. A, Patient 1: the arrow (white and black) marks the abscess on US and CT. B, Patient 2: the arrow (white and black) marks the abscess on US and CT. C, Patient 3: the arrow (white and black) marks the thickened bowel walls of the involved terminal ileum loop on US and CT. D, Patient 4: the arrow (white and black) marks the abscess on US and CT. Note the significant reduction in the size of the abscess after the drainage as demonstrated in the US image.
Patient 2: A 32-year-old male with ileocolonic CD treated with ustekinumab presented with right lower abdominal pain and fever (38.3 °C). Abdominal CT on admission demonstrated a thickened bowel wall of a long distal ileum segment and an adjacent abscess with a measured diameter of 3 cm. Antibiotic therapy was started. Fusion US performed 2 days later demonstrated similar findings. The patient improved slowly, and during the next 6 weeks underwent 4 additional US fusion examinations facilitated by exact localization of the abscess through the fused CT imaging (Figure 1B). These sequential studies demonstrated slight reduction of the abscess diameter to 2 cm with minimal change in the bowel wall thickness. Due to fusion evidence for nonresolution of the abscess precluding optimization of immune-modulating biologic therapy, the patient was referred to laparoscopic resection of the terminal ileum and cecum and made uneventful recovery.
Patient 3: A 29-year-old previously healthy female presented with severe abdominal pain and vomiting. Abdominal CT on admission demonstrated thickening and narrowing of the distal ileum, with a critical stricture in the distal terminal ileum and prestenotic dilatation. The patient was treated with antibiotics and steroids. Fusion US study performed 1 month later demonstrated significant reduction of bowel wall thickness and resolution of the bowel loop dilatations (Figure 1C). CD was diagnosed by endoscopy, and the patient started adalimumab therapy.
Patient 4: A 32-year-old male with CD underwent resection of the ileum and cecum due to penetrating disease. On the fifth postoperative day, he developed lower abdominal pain and fever (38.5 °C). A large abdominal collection was demonstrated on abdominal CT. Following a CT-guided drainage, the patient’s condition stabilized, and he was discharged with antibiotic therapy. One month later, he was readmitted due to worsening of abdominal pain. The patient refused to undergo another CT exam. A loco-directed fusion US study demonstrated a significant reduction in the size of the collection (Figure 1D). Antibiotic therapy was restarted, and the patient was discharged.
Discussion
This pilot case-series reports for the first time, to our knowledge, the use of fusion CT and US imaging for follow-up of CD patients presenting with intraluminal and extraluminal complications. In all 4 cases, US-CT fusion proved helpful to our decision-making process. A need for repeat imaging of the abdomen is common in CD, mainly for the diagnosis and follow-up of luminal and extraluminal complications. CT scan is still the most common imaging modality used in acute settings,5 and a substantial subset of CD patients are exposed to high radiation cumulative doses.6 The main breakthrough advantage of the fusion technique is to allow the reproduction of the US image on a previous CT image, in the exact location and plane, enabling accurate follow-up with exact measurements and comparison with previous findings. In turn, this obviated the need for repeated CT scans, thereby reducing patients’ radiation exposure, and the need for repeated magnetic resonance imaging with associated non-negligible costs and lower accessibility.
In conclusion, we describe for the first time, to our knowledge, the use of fusion of bowel US-CT images for the follow-up of CD and CD-related complications. This technique appears promising, enabling precise follow-up of CD patients without the need for repeated CT scans. Further prospective studies are needed to examine the impact of this technique on diagnosis and follow-up of CD.
Conflict of Interest
Dan Carter: Consulting fees from Takeda, Abbvie, Taro, and Lapidot; speaker fees and/or research support from Takeda, Abbvie, Janssen, and Lapidot.
Shomron Ben Horin: Consulting and advisory board fees and/or research support from AbbVie, MSD, Janssen, Takeda, and CellTrion; speaker fees from Abbvie, Janssen, and Takeda; research support from Takeda and Janssen; consulting fees from Takeda and CTS.
Nir Horesh: Nothing to declare.
Olga Saukhat: Nothing to declare.
REFERENCES
