Overview of vascular imaging modalities

297

Vascular specialists spoke about the use of imaging in carotid, venous, thoracic, abdominal aortic aneurysm and lower limb procedures at the CX Vascular Imaging Course, London, UK.  

Hence JM Verhagen, Erasmus University Medical Center, Rotterdam, The Netherlands, highlighted the importance of technology-based planning in vascular interventions such as EVAR and TEVAR. In the session,‘Getting the most out of CT angiography’ he stated, “Ninety per cent of the ‘battle’ is won or lost before starting the case.” Planning must be based on proper computed tomography angiography using a dedicated workstation.”

 

Verhagen encouraged the use of 3D technology on modern therapy of vascular disease. “3D reconstruction enables morphologic assessment that is not possible using conventional axial imaging. In the highly innovative field of vascular interventions, CTA with dedicated 3D software has to go hand-in-hand with stent technology to get the best possible treatment outcome for our patients,” he commented.

 

To answer the question if CTA is absolutely necessary, he said, “Depends on how you want your results to be, how long you want your procedure to last in theatre, and how much radiation and contrast you want to use on your patient.”

 

Rachel E Clough, London, UK, told CX delegates that magnetic resonance imaging has advantages over computed tomography.

 

“Computed tomography provides a fast and non-invasive method of gathering anatomical information over large fields of view, and in many centres forms the mainstay of both pre and post procedure imaging. MRI, however, is able to provide detailed cellular, molecular, tissue and organ functional and anatomical information in a single non-ionising examination and represents a rapidly expanding area of innovation and technology research,” Clough said.

 


Carotid imaging



Alison Halliday, University of Oxford, UK, stated that for large-scale clinical trials with many patients, duplex is probably enough to give a generalisable answer, however, she also mentioned, “Where carotid endarterectomy is being compared with carotid artery stenting, it will be necessary to use additional computed tomography angiography or magnetic resonance imaging to ensure appropriate patient selection.”

William A Gray, Columbia University, Medical Center, USA, spoke about the use of duplex imaging in carotid disease. Gray said that duplex examination of the native carotid artery is “Easily performed in multiple settings, highly accurate and reproducible in qualified labs.” However, he mentioned, “It does not provide anatomic guidance beyond the cervical carotid.”

 

Gray suggested that duplex examination post carotid endarterectomy and carotid artery stenting require adjustment of interpretation, and can be highly correlated with angiographic findings. “When combined with transcranial Doppler, it can give important physiologic information,” Gray concluded.

 

Klaus Mathias, Dortmund, Germany, said that CT angiography gives “better orientation” before carotid artery stenting. Mathias commented that CT angiography helps to confirm the existence of carotid disease. It shows the degree of stenosis, type of plaque, level of calcification and degree of tortuosity of the artery. It also helps in the selection of the technique to be used, selection of points for carotid artery stenting and gives information on additional vascular pathology, he added.  Mathias recommended no use of CT angiography when the patient presents renal failure.

 

Sumaira Macdonald, Newcastle, UK, told delegates that the remit of carotid imaging is to confirm the degree of stenosis at the carotid bifurcation in order to identify those who would benefit from intervention and exclude alternative sources of emboli which may be implicated in stroke.

 

“A systematic review published in 2006 highlighted that contrast-enhanced magnetic resonance angiography (CEMRA) had the highest sensitivity, specificity and the least heterogeneity of all the non-invasive imaging modalities utilised to assess degree of stenosis. This publication has informed both the National Stroke Strategy and NICE transient ischaemic attack/stroke guidelines which both place great emphasis on CEMRA for first line or confirmatory imaging. As carotid duplex can only directly insonate the cervical portion of the carotid artery, it is an inappropriate tool to exclude alternative sources of emboli.

 

“CEMRA can easily be added to the work-up of patients requiring intervention; UK guidelines favour DWI MRI brain imaging for these patients and an MR angiogram can be added to the imaging paradigm without unnecessary fuss. Such imaging will confirm the degree of stenosis and exclude alternative sources of emboli. Most active stroke units have access to such imaging, and it is no longer feasible to argue that such ‘sophisticated’ tests delay time to intervention,” she said.

 

Ross Naylor, Leicester, UK, said that before using imaging to treat patients with carotid stenosis he needs to be sure that the imaging modality is reliable, accurate and validated. He also needs to be sure that he has the protocols for supplementary investigations as required, patients’ selection for surgery is appropriate, he is not introducing unnecessary delays to treatment and that he can complete any proposed procedure safely.

 

“In reality, I, as a surgeon, rarely need to worry about the status of the aortic arch, the presence of undiagnosed inflow disease, the presence of luminal thrombus, the presence of undiagnosed distal internal carotid artery disease and intracranial stenosis or intracranial aneurysms,” Naylor said.

 


Venous imaging

 


Carsten Arnoldussen, Maastricht, The Netherlands, told delegates how magnetic resonance imaging is becoming the standard for visualisation of the venous system. Arnoldussen said, “Magnetic resonance imaging permits full overview of the deep venous system with visualisation of collateral pathways, high resolution reconstructions in any plane and depiction of surrounding structures in high resolution.” Unlike CT scans, magnetic resonance imaging does not produce radiation, he added. Among the limitations to use magnetic resonance imaging, Arnoldussen mentioned, the presence of contrast nephropathy, non-MRI compatible electronic implants such as pacemakers and recent implantation of metal stent-grafts.

Abdominal aortic aneurysm imaging


 

Jesper Swedenborg, Solna, Sweden, spoke about imaging for rupture risk. Currently, treatment for aneurysm patients is largely based on the maximum diameters measured on the CTA data of the patient although sometimes the surgeon has additional patient information which motivates an earlier intervention. With the reduced risks associated with minimally invasive surgery, the most relevant question is when the operative risk favours the risk of aneurysm rupture, he said. Two new parameters are available to help the decision when to operate. Both the location of the weakest area within the aneurysm and the peak wall rupture risk are parameters which have been included in different studies and are available in the new software A4clinics.

 

Richard McWilliams, Liverpool, UK, spoke on ‘Abdominal radiographs after EVAR for abdominal aortic aneurysms.’ With various examples, McWilliams told delegates how radiographs help to document position of stents after EVAR. Anchor stent changes, stent detachment, barbs engagement or fractures and neck dilatation are possible to detect with radiographs, McWilliams said.

 

Jos C van den Berg, Lugano, Switzerland, spoke about the valuable use of dual-energy computed tomography scan after EVAR. Van den Berg said that conventional CT is limited to one contrast and displays only morphological information, while dual-energy CT is able to identify different tissues. “Dual energy uses tubes at 80 kV and 140 kV for differentiated attenuation of tissue such as calcium and iodine,” he added.

 

Van den Berg said that EVAR follow-up and peripheral CT angiography are part of the main applications of dual-energy CT scan in the vascular field. A reliable detection of endoleaks and the reduction of radiation exposure are the main advantages identified in the use of dual-energy CT for EVAR follow-up. Van den Berg made reference to a study published last year by Sommer et al in the Journal of Vascular and Interventional Radiology which concluded, “Dual-energy CT makes a reliable detection of endoleaks feasible in a single acquisition. This provides a potential dose reduction for patients who have to undergo lifelong follow-up examinations after endovascular aneurysm (44–61%).” This may also allow for reduction of contrast used, due to the better attenuation of contrast at a low energy acquisition, van den Berg added.

 

With regards to peripheral CT angiography, van den Berg said “Dual-energy CT yields high quality peripheral CT angiography, facilitating interpretation of images.”

 

Florian Dick, Bern, Switzerland, spoke on the value of CT scan in the management of ruptured abdominal aortic aneurysm. Dick said that pre-operation CT scan is valuable because it permits to see the aneurysm anatomy, helps in the strategy planning for repair and to choose the correct graft size, and allows to be prepared for the unexpected.

 


Lower limb

 


Patrick Peeters, Imelda Hospital, Bonheiden, Belgium, told delegates that “CT angiography is an accurate diagnostic test in the assesment of arterial disease of the lower extremity.” However, “For very calcified lesions CT angiography is of questionable diagnostic value even with the next generation CT angio scans.”

For the diagnosis in the treatment of lower limb, Peeters favoured the use of CT angiography over angiography alone. He commented, “CT angiography is less invasive, has lower complication rates, it is less expensive, provides less discomfort for the patient and gives more detailed images with the use of 3D visualisation.”

When treating very calcified superficial femoral artery lesions, Peeters commented, the calcification of the vessel wall may lead to false-negative findings of patency and the high-attenuation artifacts or “blooming” caused by calcification may lead to false-positive diagnosis of substantial stenosis, that is why in very calcified cases CT angiography is of  “questionable diagnostic value.”

 

Peeters concluded that the best treatment option for very calcified lessions needs to have several factors including: a blend of visualisation techniques such as duplex, CT angiography, MRA scan, conventional arteriography, the experience of the operator interpretating images and the medical history of the patient.

 

 

Innovation

 

 

Wladyslaw Gedroyc, Imperial College, London, UK, spoke about magnetic resonance-guided focused ultrasound (MRgFUS) and its multiple applications. MRgFUS combines two systems: magnetic resonance imaging  scanner to visualise patient anatomy, map the volume of tissue to be treated, and control the treatment by monitoring the temperature of the tissue after heating and focused beam of ultrasound energy that heats and destroys the tissue using high-intensity sound waves, commented Gedroyc. “This is the first time that MR has been used to monitor tissue temperature.” “The integration of MR imaging to focused ultrasound offers excellent visualisation of adjacent soft tissues so that beam path can be seen and high risk structures such as bowel can be avoided. MR greatly improves accuracy, reliability and safety,” Gedroyc said.

 

According to Gedroyc, MRgFUS has been used to treat uterine fibroids, liver tumours, lumbar facet joint pain, prostate cancer, breast cancer, brain tumours, among others. “Magnetic resonance-guided focused ultrasound has a huge potential. It has already been very successful for uterine fibroids, changing the way how these tumours are treated. Similar changes will happen in other areas of treatment as invasive procedures are converted into closed non-invasive ones and hospital stays may be eliminated or minimised in many areas.”

(Visited 28 times, 1 visits today)