Basic planning principles
For most routine procedures, such as percutaneous biopsy or abscess drainage, complex multistep imaging is generally not required. To obtain adequate anatomical information and establish safe access, a noncontrast imaging study (noncontrast imaging) is sufficient for the physician. In some cases, venous phase scanning (venous phase) becomes the optimal choice, clearly demonstrating the structure of parenchymal organs and the borders of fluid collections.
High-risk interventions
When planning procedures in close proximity to major blood vessels, safety becomes the priority. To prevent accidental injury to arteries and other vital structures by the operator, performing CT angiography (CTA) is strongly recommended. This method allows for detailed mapping of the vascular bed and helps avoid fatal hemorrhages during access.
Specifics of tumor ablation planning
Neoplasm destruction procedures (e.g., tumor ablation) require a highly detailed anatomical picture. Unlike simple fluid drainage, performing a multiphase imaging study (multiphase imaging) is critically important here.
A classic example is the preparation for biopsy and ablation of focal liver and kidney lesions. Multiphase scanning allows evaluation of the contrast enhancement pattern, precise determination of tumor tissue margins, and its blood supply at different stages (arterial, venous, delayed).
Risks and complications of contrast agents
When using MR navigation and planning with magnetic resonance imaging, the specific risks of contrast agents must be considered.
- Nephrogenic systemic fibrosis (nephrogenic systemic fibrosis): a severe complication developing against the background of gadolinium-based agent administration in patients with reduced renal function.
- Gadolinium deposition (gadolinium deposition): accumulation of the contrast agent in brain structures after a series of contrast-enhanced MRI scans, requiring strict justification of indications for each procedure.
Advanced CT and MRI capabilities in interventions
In addition to parenchymal interventions, tomography is critical for planning vascular and endovascular procedures:
- Neuroradiology: Assessment of the perfusion-diffusion mismatch in stroke, determination of indications for thrombectomy, visualization of cervical artery dissection and subclavian steal syndrome.
- Cardiovascular surgery: Planning of endovascular aneurysm repair (EVAR) for abdominal aortic aneurysms, selection of stent-grafts, assessment of instability predictors, and management of endoleaks.
- Abdominal and thoracic radiology: Identification of sources of acute gastrointestinal bleeding, assessment of acute mesenteric ischemia, and diagnosis of pulmonary embolism (including noncontrast MR angiography and CT angiography during pregnancy).
Briefly: answers to topical questions
What are the types of endoleaks after endovascular abdominal aortic aneurysm repair (EVAR)?
There are 5 described types of endoleaks occurring after endovascular aneurysm repair.
- Type I (Type I) — secondary leakage due to inadequate sealing at the stent-graft fixation site (1A at the proximal end, 1B at the distal end).
- Type II (Type II) — retrograde filling of the aneurysm sac via arterial branches (lumbar, inferior mesenteric).
- Type III (Type III) — mechanical damage to the graft or separation of its modular components.
- Type IV (Type IV) — secondary leakage due to graft material porosity.
- Type V (Type V) — endotension (Endotension), expansion of the aneurysm sac without visible sources of endoleak.
What methods of thermal percutaneous tumor ablation are performed under CT and MRI guidance?
The following thermal tumor ablation methods are performed under image guidance:
- Radiofrequency ablation (radiofrequency ablation) — uses thermal energy to achieve coagulative tissue necrosis.
- Microwave ablation (microwave ablation) — used for thermal destruction of tumors, may be accompanied by a massive outgassing effect.
- Cryoablation (cryoablation) — an ablation method in which hydrodissection can be used to protect adjacent structures.
These technologies aim at complete tumor destruction while preserving the surrounding functioning parenchyma.
What is included in the concept of perfusion-diffusion mismatch when determining indications for thrombectomy?
The concept of diffusion-perfusion mismatch (diffusion-perfusion mismatch) is described in literature as a method for assessing the ratio between:
- core infarct (core infarct) — the zone of irreversibly damaged tissue;
- ischemic penumbra (penumbra) — potentially viable ischemic tissue.
Advanced neuroimaging aims to determine the size of the core infarct, identify viable penumbral tissue, and assess the size and severity of ischemia within the penumbra zone. Perfusion MRI can be used to detect perfusion-diffusion mismatch.
Class and exam questions
Which CT phase is sufficient for planning abscess drainage?
In most cases, a non-contrast study or a scan in the venous phase (venous phase) is sufficient for safe abscess drainage.
Why is CT angiography needed in percutaneous interventions?
CT angiography (CTA) is necessary when working near major blood vessels so that the operator can visualize them and avoid accidental arterial injury.
What scanning protocol is required for kidney and liver tumor ablation?
For detailed planning of ablation and biopsy of focal parenchymal organ lesions, performing a multiphase study (multiphase imaging) is critically important.
What is the main specific risk of MRI contrast agents?
The main risks are associated with the use of gadolinium: the development of nephrogenic systemic fibrosis in patients with renal pathology and gadolinium deposition in brain structures.
What else to study on this topic
- Principles of dual-source CT in procedure planning.
- Modern capabilities of contrast-enhanced MR angiography.
- Assessment of perfusion-diffusion mismatch in stroke and indications for thrombectomy.
- Diagnosis and management of endoleaks after endovascular treatment of abdominal aortic aneurysms (EVAR).
- CT semiotics of acute mesenteric ischemia and ischemic colitis.
- Diagnosis of pulmonary embolism during pregnancy: CT angiography compared with perfusion scanning.
Master the entire topic in the "Diagnostic Radiology" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Planning of percutaneous interventions under CT and MRI guidance" and 2,199 more pages on the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 10 video lessons on the subject
Other topics in the "Interventional radiology" section
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.