Clinical applications
Hybrid operating rooms are currently used mainly in cardiac, vascular and neurosurgery, but could be suitable for a number of other surgical disciplines.Cardiovascular surgery
The repair of diseased heart valves and the surgical treatment of rhythm disturbances and aortic aneurysms can benefit from the imaging capabilities of a hybrid OR. Hybrid Cardiac Surgery is a widespread treatment for these diseases. The shift towards endovascular treatment of abdominal aortic aneurysms also pushed the spread of angiographic systems in vascular operating room environments. Particularly for complex endografts, a hybrid operating theater should be a basic requirement. Also, it is well-suited for emergency treatment. Some surgeons not only verify the placement of complex endografts intraoperatively, they also use their angiography system and the applications it offers for planning the procedure. As anatomy changes between a preoperative CT and intraoperativeNeurosurgery
In Neurosurgery, applications for hybrid ORs are for example spinal fusion and intracranial aneurysm coiling. In both cases, they have been rated promising to improve outcomes. For spinal fusion procedures, an integration with a navigation system can further improve the workflow. Intraoperative acquisition of a cone beam computed tomography image can also be used to reconstruct three dimensional CT-like images. This may be useful for the applications above and also for confirmation of targeting for placement of ventricular catheters, biopsies, or deep brain stimulation electrodes. Intra-operative MRI is used to guide brain tumor surgery as well as placement of deep brain stimulation electrodes and interstitial laser thermal therapy.Thoracic surgery and endobronchial procedures
Procedures to diagnose and treat small pulmonary nodules have also recently been performed in hybrid operating rooms. Interventional image guidance thereby offers the advantage of precisely knowing the position of the nodules, particularly in small or ground-glass opaque tumors, metastases, and/or patients with reduced pulmonary function. This allows for a precise navigation in biopsies, and resection inBiopsy
Small lung nodules identified on a thorax CT need to be examined for malignancy, thus a small portion of sample tissue is taken out in a needle procedure. The needle is advanced through the bronchial tree, or trans-thoracically, towards the position of the nodule. To make sure tissue is captured from the nodule as opposed to accidentally taking healthy lung tissue, imaging modalities such as mobile C-Arms, ultrasound, or bronchoscopes are used. The yield rate of biopsies in small nodules is reported to be between 33 and 50% in tumors smaller than 3 cm. To increase the yield rate, advanced interventional imaging with angiographic C-arms has proven to be beneficial. The advantage of intra-procedural imaging is that the patient and the diaphragm are in exactly the same position during 2D/3D imaging and the actual biopsy. Hence the accuracy is usually much higher than using pre-operative data. Rotational angiography visualizes the bronchial tree in 3D during the procedure. The air thereby serves as a ‘natural’ contrast agent, thus the nodules are well visible. On this 3D image, using dedicated software, the nodules can be marked, along with a planned needle path for the biopsy (endobronchially or trans-thoracically). These images can then be overlaid on live fluoroscopy. This gives the pulmonologist improved guidance towards the nodules. Yield rates of 90% in nodules of 1–2 cm, and 100% in nodules > 2 cm have been reported with this approach.Surgery
Video-assisted thoracoscopic surgery is a minimally-invasive technique to resect lung nodules that saves the patient the trauma of a thoracotomy. Thereby, small ports are used to access the pulmonary lobes and introduce a camera on a thoracoscope, along with the necessary instruments. While this procedure speeds up recovery and potentially reduces complications, the loss of natural vision and tactile sensing makes it difficult for the surgeon to locate the nodules, especially in cases of non-superficial, ground-glass opaque, and small lesions. The yield rate for nodules < 1 cm can be below 40% as studies show. As a consequence sometimes more healthy tissue is resected than actually necessary in order to avoid missing (parts of) the lesion. Using advanced intra-operative imaging in the operating rooms helps to precisely locate and resect the lesion in a potentially tissue-sparing and quick fashion. In order to be able to use image guidance during video-assisted thoracoscopic surgery, rotational angiography has to be performed before the introduction of ports, thus before the lobe in question deflates. This way the lesion is visible through the natural contrast of air. In a second step, hook wires, thread needles, or contrast agent (lipiodol, iopamidol) are introduced into or next to the lesion to ensure visibility on the angiogram after lung deflation. Then, the conventional part of video-assisted thoracoscopic surgery starts with the introduction of thoracoscopes. The imaging system is used in fluoroscopic mode now, where both the inserted instruments and the previously marked lesion are well visible. A precise resection is now possible. In case contrast agent has been used to mark the lesion, it will also drain into the regional lymph nodes, which then can be resected within the same procedure.Orthopedic trauma surgery
Complex fractures like pelvis fractures, calcaneus or tibia head fractures, etc. need an exact placement of screws and other surgical implants to allow quickest possible treatment of the patients. Minimally invasive surgical approaches result in less trauma for the patient and quicker recovery. However, the risk of malpositionins, revisions and nerval damage cannot be underestimated (Malposition and revision rates of different imaging modalities for percutaneous iliosacral screw fixation following pelvic fractures: a systematic review and meta-analysis). The possibility of the use of an angio system with a spatial resolution of 0.1 mm, the large field of view to image the entire pelvis in one image and the high kW rate allows the surgeon high precision images while not impairing hygiene (floor mounted systems) or access to the patient (CT). Degenerative spine surgery, traumatic spinal fractures, oncologic fractures or scoliosis surgery are other types of surgery that can be optimized in a hybrid OR. The large field of view and the high kW rate allow to optimally image even obese patients. Navigations systems or the use of integrated laser guidance can support and improve the workflow.Laparoscopic surgery
As in other minimally invasive surgery, not everybody in the surgical community did not believe in this technology. Today it is the gold standard for many types of surgery. Starting with a simple appendectomy, cholecystectomy, partial kidney resections and partial liver resections, the laparoscopic approach is expanding. The image quality, the possibility of imaging the patient in the surgical position and the guidance of the instruments facilitate this approach.(Efficacy of DynaCT for surgical navigation during complex laparoscopic surgery: an initial experience. Partial resection of the kidney, leaving as much healthy tissue, meaning kidney function to the patient has been described.). The challenges the surgeons face is the loss of natural 3D vision and tactile sensing. Through small ports he/she has to rely on the images provided by the endoscope and is unable to feel the tissue. In a hybrid operating room the anatomy can be updated and imaged in real time. 3D images can be fused and/or overlaid on live fluoroscopy or the endoscope. (Real-time image guidance in laparoscopic liver surgery: first clinical experience with a guidance system based on intraoperative CT imaging.) Crucial anatomy like vessels or a tumor can be avoided and complications reduced. Further investigations are under trial at the moment. (Surgical navigation in urology. European perspective)Emergency care
For the treatment of trauma patients, every minute counts. Patients with severe bleeding after car accidents, explosions, gunshot wounds or aortic dissections, etc. need immediate care due to the life-threatening blood loss. In a hybrid operating room both open and endovascular treatment of the patient can be performed. For example, the tension in the brain due to a severe haemorrhage can be relieved and the aneurysm can be coiled. The concept of placing the emergency patient on an operating table as soon as he/she enters the hospital, if stable perform a trauma scan in the CT or if unstable immediate procedure in the hybrid operating room without having to reposition the patient can save valuable time and reduce risk of further injury.Imaging techniques
Imaging techniques with a fixed C-Arm
Fluoroscopy and data acquisition
Rotational Angiography
Rotational angiography is a technique to acquire CT-like 3D images intraoperatively with a fixed C-Arm. To do that, the C-Arm is rotated around the patient, acquiring a series of projections that will be reconstructed to a 3D data set.Digital subtraction angiography
Digital subtraction angiography (DSA) is a two-dimensional imaging technique for the visualization of blood vessels in the human body (Katzen, 1995). For DSA, the same sequence of a projection is acquired without and then with contrast agent injection through the vessels under investigation. The first image is subtracted from the second to remove background structures such as bones as completely as possible and show the contrast-filled vessels more clearly. As there is a time lag between the acquisition of the first and the second image, motion correction algorithms are necessary to remove movement artifacts. An advanced application of DSA is road mapping. From the acquired DSA sequence, the image frame with maximum vessel opacification is identified and assigned to be the so-called road-map mask. This mask is continuously subtracted from live2D/3D registration
= Fusion imaging and 2D/3D overlay
= Modern angiographic systems are not just used for imaging, but support the surgeon also during the procedure by guiding the intervention based on 3D information acquired either pre-operatively or intra-operatively. Such guidance requires that the 3D information is registered to the patient. This is done using special proprietary software algorithms.= Information flow between workstation and angiographic system
= 3D images are calculated from a set of projections acquired during a rotation of the C-Arm around the patient. The volume reconstruction is performed on a separate workstation. The C-Arm and the workstation are connected a communicate continuously. For example, when the user virtually rotates the volume on the workstation to view the anatomy from a certain perspective, the parameter of this view can be transmitted to the angio system, which then drives the C-arm to exactly the same perspective for= Overlay of 3D information on top of 2D fluoroscopy
= The 3D image itself can be overlaid colour-coded on top of the fluoroscopic image. Any change of the angulations of the C-arm will cause the workstation to re-calculate in real-time the view on the 3D image to match exactly the view of the live 2D fluoroscopy image. Without additional contrast agent injection the surgeon can observe device movements simultaneously with the 3D overlay of the vessel contours in the fluoroscopy image. An alternative way to add information from the workstation to the fluoroscopic image is to overlay, after either manual or automatic segmentation of the anatomical structures of interest in the 3D image, the outline as a contour onto the fluoroscopic image. This provides additional information that is not visible in the fluoroscopic image. Some software available provides landmarks automatically, more can be added manually be the surgeon or a qualified technician. One example is the placement of a fenestrated stentgraft to treat an= Guidance during trans-aortic valve implantation
= Trans-Aortic Valve Implantation requires exact positioning of the valve in the aortic root to prevent complications. A good fluoroscopic view is essential, whereby an exact perpendicular angle to the aortic root is considered to be optimal for the implantation. Recently, applications have been released which support the surgeon in selecting this optimal fluoroscopy angulation or even drive the C-arm automatically into the perpendicular view to the aortic root. Some approaches are based on pre-operative CT images, which are used to segment the aorta and calculate optimal viewing angles for valve implantations. CT images must be registered with C-arm CT or fluoroscopic images to transfer the 3D volume to the actual angiographic system. Errors during the registration process might result in diversification from the optimal angulations of the C-arm and must be manually corrected. Additionally, anatomical variations between the acquisition of the pre-operatively CT image and surgery are not accounted for. Patients are generally imaged with hands-up in a CT scanner while surgery is performed with arms aside the patient, which leads to substantial errors. Algorithms purely based on C-arm CT images acquired in operating rooms by the angiographic system are inherently registered to the patient and show the present anatomy structures. With such an approach, the surgeon does not rely on pre-operative CT images acquired by the radiology department, which simplifies the workflow in the operating room and reduces errors in the process.Functional imaging in the operating room
Improvements of the C-Arm technology nowadays also enable perfusion imaging and can visualize parenchymal blood volume in the OR. To do that, rotational angiography (3D-DSA) is combined with a modified injection protocol and a special reconstruction algorithm. The blood flow can then be visualized in the course of time. This can be useful in the treatments of patients withImaging techniques with a CT
A CT system mounted on rails can be moved into and out of an operating room to support complex surgical procedures, such as brain, spine and trauma surgery with additional information through imaging. The Johns Hopkins Bayview Medical Center in Maryland describes that their intra-operative CT usage has a positive impact on patient outcomes by improving safety, decreasing infections and lowering the risks of complications.Imaging techniques with magnetic resonance tomography
Magnetic resonance imaging is used in neurosurgery: # Before surgery to enable precise planning # During surgery to support decision making and accounting for brain shift # After surgery to evaluate the outcome An magnetic resonance tomography system usually requires a lot of space both in the room and around the patient. It is not possible to perform surgery in a regular magnetic resonance tomography room. Thus for step 2, there are two ways to use magnetic resonance scanners interoperatively. One is a moveable magnetic resonance tomography scanner that can be brought in only when imaging is needed, the other is to transport the patient to a scanner in an adjacent room during surgery.Planning considerations
Location/ Organization
Not only the usage of a hybrid operating room is "hybrid", but also its role within the hospital system. As it holds an imaging modality, the radiology department could take the lead responsibility for the room for expertise in handling, technical, maintenance, and connectivity reasons. From a patient workflow perspective, the room could be run by their surgical department and should rather be situated next to other surgical facilities, to ensure proper patient care and fast transportation.Room size and preparation
Installing a hybrid operating room is a challenge to standard hospital room sizes, as not only the imaging system requires some additional space, but there are also more people in the room as in a normal OR. A team of 8 to 20 people including anesthesiologists, surgeons, nurses, technicians, perfusionists, support staff from device companies etc. can work in such an OR. Depending on the imaging system chosen, a room size of 70 square meters including a control room but excluding a technical room and the preparation areas is recommended. Additional preparations of the room necessary are 2-3mm lead shielding and potentially enforcement of the floor or ceiling to hold the additional weight of the imaging system (approximately 650–1800 kg).Workflow
Planning a hybrid operating room requires to involve a considerable number of stakeholders. To ensure a smooth workflow in the room, all parties working there need to state their requirements, which will impact the room design and determining various resources like space, medical, and imaging equipment. This may require professional project management and several iterations in the planning process with the vendor of the imaging system, as technical interdependencies are complex. The result is always an individual solution tailored to the needs and preferences of the interdisciplinary team and the hospital.Lights, monitors and booms
In general, two different light sources are needed in an operating room: the surgical (operating) lights used for open procedures and the ambient lighting for interventional procedures. Particular attention should be paid to the possibility to dim the lights. This is frequently needed duringImaging systems
The most common imaging modality to be used in hybrid ORs is a C-Arm. Expert consensus rates the performance of mobile C-arms in hybrid ORs as insufficient, because the limited power of the tube impacts image quality, the field of view is smaller for image-intensifier systems than for flat-panel detector systems and the cooling system of mobile C-Arms can lead to overheating after just a few hours, which can be too short for lengthy surgical procedures or for multiple procedures in a row, that would be needed to recover the investment in such a room. Fixed C-Arms do not have these limitations, but require more space in the room. These systems can be mounted either on the floor, the ceiling, or both if a biplane system is chosen. The latter is the system of choice if pediatricOperating room table
The selection of the operating room table depends on the primary use of the system. Interventional tables with floating table tops and tilt and cradle compete with fully integrated flexible operating room tables. Identification of the right table is a compromise between interventional and surgical requirements. Surgical and interventional requirements may be mutually exclusive. Surgeons, especiallyRadiation dose
X-ray radiation is ionizing radiation, thus exposure is potentially harmful. Compared to a mobile C-Arm, which is classically used in surgery, CT scanners and fixed C-Arms work on a much higher energy level, which induces higher dose. Therefore, it is very important to monitor radiation dose applied in a hybrid operating room both for the patient and the medical staff. There are a few simple measures to protect people in the operating room from scatter radiation, thus lower their dose. Awareness is one critical issue, otherwise the available protection tools might be neglected. Among these tools is protective clothing in the form of a protective apron for the trunk, a protective thyroid shield around the neck and protective glasses. The later may be replaced by a ceiling-suspended lead glass panel. Additional lead curtains can be installed at the table side to protect the lower body region. Even more restrictive rules apply to pregnant staff members. A very effective measure of both protection to both the staff and the patient of course is applying less radiation. There is always a trade-off between radiation dose and image quality. A higher x-ray dose leads to a clearer picture. Modern software technology can improve image quality during post-processing, such that the same image quality is reached with a lower dose. Image quality thereby is described by contrast, noise, resolution and artifacts. In general, theReferences
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