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Parametric contrast enhanced ultrasound evaluation of transarterial chemoembolization
Thesis   Open access

Parametric contrast enhanced ultrasound evaluation of transarterial chemoembolization

Minakshi Mohanty
Master of Science (M.S.), Drexel University
01 Jun 2015
DOI:
https://doi.org/10.17918/etd-6503
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Abstract

Contrast-enhanced ultrasound Contrast-enhanced magnetic resonance imaging Biomedical Engineering
This work investigates quantitative contrast enhanced ultrasound (CEUS) derived blood flow parameters for evaluating chemoembolization of hepatocellular carcinoma. Hepatocellular carcinoma (HCC) is the third leading cause of cancer mortality worldwide and is becoming increasingly common. Liver transplant is the only cure with 70 percent 5 year survival rate. However, transplant requires the tumor to fall under the Milan criteria (less than 5cm or up to 3 nodules each less than 1cm) and the technique is limited by the availability of donors. Transarterial chemoembolization (TACE), currently, is a treatment option for non-resectable tumors. It involves the administration of drug eluting beads via catheter into the branch of the hepatic artery that feeds the tumor. These beads occlude the blood supply to the tumor and at the same time release chemotherapy, leading to necrosis of the tumor and reduction in its size. Presently, the effectiveness of TACE procedure is determined one month post embolization through the use of contrast enhanced magnetic resonance imaging (MRI) or computed tomography (CT) scans, by evaluating blood flow within the tumor. Early screening for effective chemoembolization with contrast-enhanced MRI has been proven ineffective due to an inability to adequately visualize the vasculature. An earlier estimation of treatment efficacy would provide clinicians more time and options for re-treatment. Additionally, a number of patients may have morbidities including renal insufficiency. These patients may develop nephrogenic systemic fibrosis, which is the necrosis of skin and the internal organs, on exposure to gadolinium (present in MRI contrast agents). This project proposes the use of contrast enhanced ultrasound (CEUS) for monitoring the effectiveness of transarterial chemoembolization. Ultrasound contrast agents are gas filled microbubbles, which are encapsulated within a thin elastic shell made of lipids. They have a diameter of 1-10[mu]m. Due to their restriction to the vasculature, an absence of contrast within the tumor is expected in cases where complete embolization has been achieved. Earlier studies have shown that lack of detected agents as little as 2 days post procedure correlated with effective procedure. However, currently there is no established standard as to how many days post treatment should the follow up be conducted, or which contrast agent to use. Fourteen patients with 16 lesions scheduled for transarterial chemoembolization (TACE) of HCC using drug eluting beads provided informed consent to undergo CEUS exam prior to treatment, 2 weeks post treatment, and the morning of follow up (contrast enhanced MRI 1 month post TACE). Ultrasound was performed using a Sequoia 512 scanner with 4C1 probe (Siemens Medical Solutions, Mountain View, CA). CEUS data was acquired using Cadence Pulse Sequencing (Siemens) during bolus injection of 0.6-0.7 ml of Definity (Lantheus Medical Imaging, N. Billerica, MA). Motion compensation was performed and time intensity curves were generated on a pixel-by-pixel basis to create parametric images showing maximum signal intensity (MAX), time to peak intensity (TTP), perfusion (PER), and area under curve (AUC). These values were averaged over the tumor and expressed normalized relative to baseline. Results were then grouped by clinical diagnosis (fully treated (n=5), partially treated (n=5) or no change (n=6)) and compared at each time point. Parametric imaging was successfully performed on 10 lesions, while six were excluded due to inability to identify tumor. Significant difference was observed in the time to peak dataset 2 weeks post TACE between complete response and no response group (p=0.018). No significance was observed in maximum intensity, perfusion and area under curve dataset. In the time intensity parameters obtained 4 weeks post TACE, no significant difference was observed. In conclusion, time to peak currently appears to be a good quantitative CEUS parameter for evaluating the effectiveness of TACE treatment 2 weeks post treatment.

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