iRADiX

In broad terms, diagnostic imaging offers the clinical investigator two principal types of information. Most imaging techniques provide information on macrosopic structure, by revealing the anatomy of organs and the morphology of lesions. A second major focus of imaging techniques is the circulatory system, in particular the vascularity of tissues and their perfusion by blood. Future diagnostic imaging modalities, currently used only in research settings, can provide information at the molecular level, such as the concentration of metabolites and the tissue density of proteins (e.g. receptors, enzymes).

Ultrasound (USG) provides information on both macroscopic structure and blood circulation. The capabilities of ultrasound can be improved and expanded by the use of a contrast agent, which does much more than simply improve the signal-to-noise ratio or compensate for inadequate instrumentation!

The role of contrast-enhanced ultrasound (CEUS) in liver imaging is very well established. However, its application in other organs is still controversial.

Herein I will describe a series of clinical examples to illustrate some of the varied uses of contrast-enhanced ultrasound beyond the common application in the study of focal liver lesions.

Lung

A patient was diagnosed at CT with a large abscess in the right lung (Figure 1) and sent to the ultrasound department for placement of a drain. Plain USG did not reveal a fluid collection. CEUS showed a large lesion with intense enhancement of peripheral areas during arterial phase, while the central area of the lesion remained dark; there was no evidence of septa, typically seen in abscesses. A biopsy from the wall revealed a necrotic adenocarcinoma.

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Figure 1 (a-c) : Large lesion in lung misdiagnosed as abscess. (a) CT scan suggested diagnosis of lung abscess. (b) Plain ultrasound showed a ‘solid-looking’ lesion. (c) CEUS showed peripheral enhancement in the arterial phase around a necrotic core suggesting necrotic cancer.

Biliary system

CEUS is increasingly used before ERCP to map the biliary tree. CEUS is also being used in the investigation of intrahepatic gallstones. In our experience, intrahepatic gallstones are better visualized against a background of enhancing liver parenchyma.

The diagnosis of Gall bladder cancer is a challenge. We used CEUS to look for malignant polyps in a few referred cases. When enhancement of the suspected “sludge” is seen, a diagnosis of malignancy is likely (Figure 2).

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Figure 2 (a-d) : Search for Gall bladder malignancy using plain & CEUS. a,c Plain USG images from two patients do not reveal any clues regarding malignancy. b, d CEUS images of the same patients show that (b) lumen remains dark, while the other (d) has enhancement of the contents (arrow), suggesting malignancy.

Kidney

A patient presented with sudden flank pain. At CT scan, an indeterminate abnormality was observed in left kidney. (Figure 3). Conventional USG did not provide diagnostic information, so CEUS was used. This allowed us to identify, along the edge of kidney, a wedge-shaped infarction with clear margins, shown as an area of signal void.

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Figure 3 a, b: Diagnosis of kidney infarction in a patient with sudden left flank pain. CT image identified an indeterminate abnormality (arrow) of the left kidney. CEUS revealed a ‘wedge-shaped’ area of signal void (arrow) suggesting cortical infarct.

A neonate had hematuria 3 days after birth. On plain USG the right kidney was dysmorphic with only a small area having normal morphology. (Figure 4). On color Doppler, no blood flow was seen in the abnormal part of kidney. In order to differentiate between infarction and tumor, we performed CEUS which showed complete lack of contrast enhancement in the left kidney, with the exception of the small area having normal structure, and thereby excluding the possibility of viable tumor. A 2 month follow-up examination showed atrophied kidney, confirming the diagnosis of infarction.

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Figure 4 a, b: Investigation of hematuria in a 3-day-old neonate. Plain USG (a) revealed abnormal structure (arrow) of left kidney. CEUS (b) showed lack of enhancement in this abnormal structure, excluding tumor and confirming infarction.

Spleen

The splenic lesions behave similar to liver lesions on contrast imaging, especially regarding ‘wash-out’ sign. However, the initial enhancement of spleen is heterogenous, requiring the operator to wait 40-50 sec. before imaging. After this wait period, it is possible to detect splenic malignancy and infarction on the basis of the hypoechogenic appearance. (Figure 5).

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Figure 5 a, b: CEUS of spleen. a Spleen enhances heterogeneously in arterial phase. b After 1 minute, it becomes possible to identify infarction (arrows).

Portal vein

We have studied suspected portal vein thrombosis with color Doppler USG. The problem arises when we have to differentiate between bland thrombus and tumor thrombus and color Doppler is not always helpful. CEUS helps in such situations, and also in post-liver transplant patients.

Abdominal trauma

Polytrauma patients with severe injuries should always be subjected to MDCT. But for young and cooperative patients with stable injuries, CEUS can be al appropriate examination.

A 9-year old girl fell down from height in the evening and underwent CT examination in trauma department, which was assessed as “normal” and patient discharged. The next day, patient came back with persistent frank hematuria. Plain USG revealed a small perinephric collection. CEUS showed the tear within the renal parenchyma to be the cause of perinephric collection and hematuria. (Figure 6). Previous CT scan images were reviewed again and renal parenchymal tear diagnosed retrospectively, only to be suggested by CEUS.

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Figure 6 a, b, c: Kidney fracture in a 9-year-old girl who fell. Plain USG (b) revealed
small fluid collection (arrow). CEUS (c) showed the kidney fracture (ROI) similar to that seen with CT scan (arrow) (a).

At the present time, CEUS is more of a ‘problem-solving’ tool than first line investigation modality. It is cost-effective, easy to perform, non-invasive and involves no ionizing radiation.

The role of CEUS in diagnosing and characterizing focal liver lesions is quite well established and is also gaining wide acceptance in post-treatment follow-up, especially after radio-frequency ablation

The future of CEUS looks promising and I am quite certain that CEUS will play a very vital role in body imaging in years to come.