Non-invasive Imaging of GI Inflammation Using Microbubble Contrast Enhanced Ultrasonography

GI inflammation may indicate a number of complications or diseases, one of which is
inflammatory bowel disease (IBD), now the second most prevalent inflammatory disorder in the
world. Symptoms of the disease include severe abdominal pain, bloody diarrhea, persistent
fever, weight loss, and significant malnutrition. There is also an increased risk of colon
cancer. If left untreated, the disease is debilitating. Prompt intervention may reduce the
amount of immunosuppressive therapy that is required to control the disease, but by the time
the patient becomes symptomatic, the inflammatory response is difficult to suppress and much
of the damage has already been done. It is therefore important to closely monitor patients
with IBD. The location, extent, and severity of the inflammation are of primary consideration
for correct diagnosis and treatment. However, no inexpensive and non-invasive procedure
exists in protocol for the assessment of these factors of IBD. A non-invasive diagnostic that
can detect the onset of inflammation and measure the extent of inflammatory involvement would
be a valuable tool for the evaluation of patients with IBD.

Endoscopy, barium contrast X-ray studies, computed tomography (CT), magnetic resonance
imaging (MRI), and transabdominal ultrasound (US) are currently the most common procedures
used by gastroenterologists. The preferred manner of investigating GI inflammation includes
endoscopy with biopsy, as only endoscopy can confirm the presence of inflammation. However,
this procedure is highly invasive and limited to areas accessible to the endoscope. There are
also limited but real risks associated with endoscopy. In addition, the cost of such a
procedure may be prohibitive, or a qualified professional inaccessible, for some patients.
Barium contrast X-ray studies remain the best way to visualize stricture and fistulae in the
small intestine, but do not provide insight into the degree and extent of active
inflammation. Repeated X-rays in chronic and younger patients also contribute to risk of
irradiation. CT and MRI are the gold-standard for imaging extra-intestinal inflammatory
disease, but fail in their ability to identify active inflammation. There have recently been
many studies attempting to improve these means of assessing GI inflammation.

Transabdominal US presents a non-invasive means of imaging internal organs that imposes no
significant health risks or undue discomfort upon the patient. The use of abdominal US for
the evaluation of IBD was implemented as early as 1979, where wall thickening of the terminal
ileum and cecum, with accompanying inflammatory changes in the mesentery, yielded
recognizable patterns in both longitudinal and transverse images.11 These initial
ultrasonographic images lacked sufficient resolution to provide a sensitive measure of
disease activity, but technological advances in high frequency US have greatly improved
resolution over the past twenty years. Still, the location and chronicity of certain
conditions may decrease the efficacy of this imaging technique, making endoscopy the
preferred method of investigation of GI problems. At present, there are several research
groups actively investigating the application of US for the management of IBD. The combined
results of these studies, in addition to the relatively wide availability, low cost, and easy
use of US equipment, support the rationale for developing US into a useful tool for the
evaluation of IBD.

Contrast-enhanced ultrasonography (CEU) is the main strategy for improving US quality. One
contrast agent that has been studied in the imaging of inflammation, but which has not yet
been human-tested for improvement of US quality in inflammation due to IBD, is microbubbles
(MB). MB contrast agents are FDA-approved, and are becoming a common clinical tool for the
enhancement of US imaging of cardiovascular hemodynamics around the world. Unlike tissue
signal, which is produced by US reflection, the strong signal generated by MB is produced by
radial oscillation of the MB in the acoustic field. Current MB used for perfusion imaging
have lipid or albumin shells and contain high-molecular weight gases (perfluorocarbons,
sulfur hexafluoride), which contribute to their high intravascular stability by preventing
outward diffusion of gas. MB are generally 2-4µm in size - smaller than average capillary
dimension - and passes unimpeded through the microcirculation. They are also hemodynamically
inert, and behave similar to red blood cells in vivo. In animal models the acoustic
properties of activated Definity® (Perflutren Lipid Microsphere) injectable suspension, were
established at or below a mechanical index of 0.7 (1.8 MHz frequency). In clinical trials,
the majority of the patients were imaged at or below a mechanical index of .08.

There are two ways that microbubbles might contribute to a strong signal in areas of
inflammation in the small intestine or colon. The first is directly through neoangiogenesis
and the increase in blood flow to the site. Defined as the growth of new blood vessels,
neoangiogenesis is important to the pathogenesis of both Crohn's disease and ulcerative
colitis. An expanded microvascular bed in the mucosa and submucosa of IBD patients with
active inflammation has been confirmed, and is consistent with the high levels of integrins
characteristic for proliferating endothelium (e.g. IL-8, bFGF, and VEGF) found in the
microvessels of tissue affected by IBD. The hope is that the increased blood flow in actively
inflamed IBD will be correlated with a stronger US signal from the increased concentration of
MB flowing through the site.

The second way microbubble CEU may be effective at identifying active inflammation is an
indirect effect of new microvasculature. Neoangiogenesis is thought to contribute to
pathogenesis by fostering the recruitment and activation of an increased number of leukocyte
into the inflamed mucosa. It has been observed that both albumin and lipid shell MB used for
echocardiographic studies are phagocytosed intact by activated leukocytes, some of which are
adherent to the inflamed endothelium of small intestine or colon. These phagocytosed MB
retain a percentage of their acoustic properties, enabling US to image inflammation
non-invasively in an in vivo setting. Incorporation of specific lipid moieties into the
microbubble shell increases retention and phagocytosis by activated leukocytes.

An investigation of the efficacy of microbubble contrast agents in imaging GI inflammation is
the first step towards such targeted imaging and tissue-targeted therapy.

Inclusion Criteria:

- Patients with inflammatory bowel disease (IBD), scheduled for diagnostic colonoscopy
or

- Patients scheduled for diagnostic colonoscopy for other indications other than IBD
(e.g. screening, family history of colon cancer).

Exclusion Criteria:

- Ineligibility for colonoscopy

- For control patients: a personal history of IBD or clinical history suspicious for IBD
or other disease associated with intestinal inflammation. To be determined by
investigators at the time of screening.

- Abnormal QT, Tic, or PR intervals during screening ECG

- Life-threatening ventricular arrhythmias during screening ECG

- Abnormally low oxygen saturation (<80%)

- History of the following:

- An intracardial or intrapulmonary shunt

- Unstable coronary artery disease

- Cerebrovascular disease (e.g. stroke or aneurysm)

- Diagnosed and or current signs or symptoms of severe, progressive or uncontrolled
congenital heart failure

- Diagnosed and/or current signs or symptoms of severe, progressive or uncontrolled
emphysema/COPD

- Diagnosed and/or current signs or symptoms of severe, progressive or uncontrolled
pulmonary hypertension (known PA pressures >50mmHg)

- Uncontrolled high blood pressure (>140/90)

- Abnormal kidney function (creatinine > 2.0 mg/dl or GFR > 90)

- Abnormal liver function (Aspartate transaminase (AST), alanine transaminase (ALT), and
alkaline phosphatase levels greater than 2 times the upper limit of normal.)

- Known hypersensitivity to octafluoropropane

- Pregnancy or nursing, confirmed by urine pregnancy test.