Extravascular (Intracavitary) CEUS Intervention Applications
General Principles:
- Ultrasound contrast agents can be instilled into any physiological or pathological body cavity to assess morphology of the cavity and potential communications with adjacent structures or organs.
- Artefacts have to be avoided: This can be achieved by using low concentration of contrast agent with adequate dilution (e.g.0.1 – 0.5 mL SonoVue® in 100 - 500 mL 0.9% saline).
Novel Clinical Applications:
CEUS Guided Percutaneous Nephrostomy (PCN) and Nephrostogram
Clinical Challenges:
- The major problem with ultrasound-guided PCN is localisation of the fine needle tip,
in particular if obesity is a factor,
or when accessing a non-dilated pelvicalyceal system.
The use of CEUS could simplify fine needle navigation in difficult cases:
Techniques:
1.
The stylet was removed from a 21G Chiba needle and the needle was flushed with a drop of ultrasound contrast agent for improved needle visualisation (Fig. 1) .
2.
On puncturing the renal calyceal system,
the microbubbles clear from the stylet as urine reflux through the needle,
giving an instant visual feedback for a successful puncture (Fig. 2).
3.
Further ultrasound contrast agent can be injected through the needle to verify correct needle positioning (Fig. 3).
Advantages of CEUS - guided Nephrostomy Insertion:
- Improved fine needle visualisation
- Instant visual feedback upon successful puncture on US
Following a successful PCN,
further diagnostic evaluation can obtained with a CEUS Nephrostogram:
Techniques:
Dilute 0.2ml of ultrasound contrast agent with 40 ml of normal saline and introduced into the renal collecting system via the nephrostomy tube.
By introducing contrast in to the collecting system,
the ureters can be followed almost all the way to the level of the bladder (Fig. 4), and drainage through the ureter can be confirmed by the presence of contrast within the bladder (Fig. 5).
Advantages of CEUS Nephrostogram:
- It is a feasible alternative to conventional fluroscopic nephrostograms to:
- Confirm the correct positioning of the nephrostomy tube within the collecting system.
CEUS examination can be performed at bedside for unstable patients.
- Image the ureters and determine if there is satisfactory drainage into the bladder.
CEUS Percutaneous Trans-hepatic Cholangiogram
Clinical Challenges:
- Potential logistical issues in transferring patient with sepsis for a conventional fluoroscopic cholangiogram.
- For patients with contraindications to iodinated contrast agents
- In children where irradiation is undesirable
Techniques:
Dilute 0.2ml of ultrasound contrast agent with 40 ml of normal saline and introduced into the biliary system via the internal-external biliary drainage tube.
Special Note: When introduced through the drainage tube,
ultrasound contrast agent should stay within the targeted compartment (in this case,
the biliary system).
If enhancement were seen elsewhere,
its distribution should be described and abnormal communication,
or mal-position of the drainage tube should be considered (Fig. 6, Fig. 7).
Advantages of CEUS Cholangiogram:
- CEUS could be performed at bedside and could simply the logistical issues in patient transfer for imaging.
The biliary drain position and external drainage for biliary obstruction in patients with severe cholangio-sepsis can be performed in the intensive care unit without X-ray guidance.
CEUS-Guided Abscess Drainage
Clinical Challenges:
- Intra-abdominal collections are a common cause of sepsis.
Abscesses demonstrate variable and sometime confusion B-mode images,
changing over time,
and is sometimes difficult to recognise.
- In addition,
these patients often require follow-up to ensure resolution.
This is usually performed with B-mode ultrasound and/or CT.
Advantages of CEUS application:
- CEUS potentially allows more accurate assessments of intra-abdominal collections compared to B-mode USS,
giving a better depiction of internal septation,
and indication of collection magnitude (Fig. 8).
- Identification of potentially necrotic or liquid collection adjacent to enhancing organs allows for a more accurate and safer drain insertion (Fig. 9, Fig. 10).
- Depiction of non-perfused areas might be relevant prior to any US-guided drainage in order to better identify target (Fig. 11).
CEUS tubograms following drain insertion allow assessment of drain patency,
position and residual cavity size.
Techniques:
0.2 ml of ultrasound contrast agent diluted in 40 ml of normal saline can be administered via the drain.
In addition,
through intravenous injection of ultrasound contrast agent,
the non-enhancing necrotic abscess or intra-parenchymal fluid collection could be dipicted and assessed (Fig. 12).
Advantages of CEUS Application:
- Follow-up of intra-abdominal collections with CEUS is radiation free,
low cost,
and can be performed at bedside in unstable patients.
CEUS Guided Tumour Ablation
Clinical Challenges:
- Certain tumours are poorly demonstrated on the baseline US scan and may only exhibit transient enhancement thus difficult to visualise on late or unenhanced CT images for precise targetiing for ablation.
Advantages of CEUS application:
- Real-time enhancement information improves the ability to differentiate between normal and abnormal tissue (Fig. 13).
- CEUS could aid lesion targeting during percutaneous ablation therapy (e.g.
hepatocellular carcinoma,
renal cell carcinoma),
particularly when the lesions are endophytic.
Vascular CEUS Applications
General Principles:
- Conventional US techniques are limited in demonstrating slow flow,
especially in flow in critical stenoses.
Aliasing and blooming artefacts and angle dependenc all affect Doppler US.
- Real-time,
angiographic information,
which is usually obtained through conventional fluoroscopic angiography,
can be acquired with CEUS without incurring radiation dose.
CEUS in Post Endovascular Aneurysm Repair (EVAR) Endoleak Management
Clinical Challenges:
- Endoleaks represent blood flow outside the stent graft lumen but within the aneurysm sac,
and are conventionally detected by CT angiography.
CT however,
does not always allow detection of some types of endoleaks.
- Most patients will be placed on life-long surveillance following aortic stent graft insertion,
with CT most commonly used which results in significant radiation burden and cost.
Advantages of CEUS application:
- Detection of endoleaks without radiation (Fig. 14).
- Because of its ability to image real-time with dynamic evaluation,
CEUS may identify and characterise endoleaks better than CT angiography,
with analysis of velocity and flow direction (Fig. 15, Fig. 16).
- The ability of CEUS in providing angiographic information allows for unique minimally-invasive percutaneous treatment option – Novel application: CEUS – Guided percutaneous percutaneous thrombin injection for type II endoleak (Fig. 17, Fig. 18).
What Lies Beneath - Arterial Puncture Site
Clinical Challenges:
- Assessment of arterial puncture site extravasation can be difficult using conventional colour Doppler US.
Frequently CT angiograms are performed to exclude puncture site complication.
Advantages of CEUS application:
- Contrast extravasation can be readily detected at bedside (Fig. 19),
allowing prompt haemostatic measures.
- CEUS may also help to image flow in false aneurysms with greater precision than colour Doppler US.
CEUS Guided Arteriovenous Fistula Angioplasty
Clinical Challenges:
- For patients with renal insufficiency not yet on dialysis,
iodinated contrast or gadolinium-based MRI contrast exposure could be detrimental
- Those with severe allergy to iodinated contrast medium in whom there is a lack of alternative angiographic contrast medium
Advantages of CEUS application:
- The novel CEUS Fistuloplasty provides real-time, ‘sonographic angiography’ (Fig. 20) while averts the detrimental effect of iodinated contrast medium.