Tattoo ink may mimic cancer on PET-CT images

Photograph by Paulo Guereta

The hit new crime thriller Blindspot is about a mysterious woman, Jane Doe, who is covered in extensive full-body tattoos. If Jane Doe were a real woman who ever needed medical imaging, she might need to be concerned.

In a case report published recently in the journal Obstetrics & Gynecology, researchers found that extensive tattoos can mimic metastases on images from positron emission tomography (PET) fused with computed tomography (CT). PET-CT imaging is commonly used to detect cancer, determine whether the cancer has spread and guide treatment decisions. A false-positive finding can result in unnecessary or incorrect treatment.

Ramez N. Eskander, MD, assistant professor of obstetrics and gynecology at UC Irvine, and his colleagues describe the case study of a 32-year-old woman with cervical cancer and extensive tattoos. The pre-operative PET-CT scan using fluorine-18-deoxyglucose confirmed that there was a large cervical cancer mass, but the scan also identified two ileac lymph nodes as suspicious for metastatic disease. However, final pathology showed extensive deposition of tattoo ink and no malignant cells in those ileac lymph nodes.

It is believed that carbon particles in the tattoo pigment migrate to the nearby lymph nodes through macrophages, using mechanisms similar to those seen in malignant melanoma. The researchers explain in their case report:

Our literature search yielded case reports describing the migration of tattoo ink to regional lymph nodes in patients with breast cancer, melanoma, testicular seminoma, and vulvar squamous cell carcinoma, making it difficult to differentiate grossly between the pigment and the metastatic disease, resulting in unnecessary treatment.

The authors warn other physicians to be aware of the possible effects of tattoo ink on PET-CT findings when formulating treatment plans, particularly for patients with extensive tattoos.

This is a reposting of my Scope blog story, courtesy of Stanford School of Medicine.

Hope for Alzheimer’s Patients?

PET image of brain using PIB
Courtesy of Dr. Jagust Lab, UC Berkeley

My mother died of Alzheimer’s at the age of 69, so I can personally attest to the horror of this disease. I can think of few things worse than slowly watching your cognitive abilities decline, particularly if you are aware of the progressive deterioration as my mother was. So I’m keeping a close watch on the latest Alzheimer’s research, including the research of my colleague William Jagust who is a neuroscientist at UC Berkeley.

Dr. Jagust is participating in the Alzheimer’s Disease Neuroimaging Initiative (ADNI), which is large multicenter project supported by NIH, private pharmaceutical companies and nonprofit organizations. The primary goal of ADNI is to discover indicators (biomarkers) that can track disease progression and hopefully diagnose Alzheimer’s early on. Basically, they want to help speed up and streamline drug and clinical trials by developing biomarkers that track Alzheimer’s more reliably.

The initial ADNI five-year research project completed last fall. It studied cognition, function, brain structure and biomarkers for 800 subjects (200 elderly controls, 400 subjects with mild cognitive impairment, and 200 subjects with Alzheimer’s). The clinical data from the patients went into a large database, including MRI scans, PET scans, blood tests, neuropsychological tests, and genetic tests. The truly unique thing is that this database can be accessed by the public through a website. Basically the raw data (with patient personal information removed) is made available for everyone to use, in hopes that this will help scientists more rapidly understand and treat Alzheimer’s. This ADNI project just received the second phase of funding, so the studies will be expanded.

Although the cause and progression of Alzheimer’s disease is not fully understood, current research indicates that the disease is associated with the formation of “amyloid plaques” and “neurofibrillary tangles” in the brain that damage nerve cells. What does this mean? Amyloid plaques are protein fragments that the body produces naturally. In a healthy brain, these protein fragments are broken down and eliminated. In a brain with Alzheimer’s, the fragments instead accumulate to form hard, insoluble plaques between nerve cells. This excess amyloid buildup occurs before clinical Alzheimer’s symptoms, so it may be used as a predictor of disease. Neurofibrillary tangles are insoluble twisted fibers found inside the brain’s cells. These  tangles mainly consist of a protein called tau, which helps form microtubules that transport nutrients from one part of the nerve cell to another. In an Alzheimer’s brain, the tau protein is abnormal and the tangles collapse this important transport system.

Dr. Jagust and other researchers are studying this beta-amyloid buildup using medical imaging, including PET imaging with a new drug called [11C]Pittsburg Compound B. This new PET drug binds to beta-amyloid plaques and indicates their size and position. “With PET, we’re able to study the biochemistry of the brain, and with MRI we can study both the anatomy and structure of the brain,” Jagust said. “We can also study some of the function of the brain to see what parts of the brain are active during different cognitive tests. So when you put all this information together, you can get a very detailed picture of how the brain is functioning and how function and structure might change with age.” Last fall Jagust published an article on the relationships between biomarkers in aging and dementia. The group found that the confluence of three factors — beta-amyloid deposition, atrophy of the hippocampus (part of the brain that stores and sorts memories), and episodic memory loss — signals early stage of Alzheimer’s. Hopefully this new understanding will ultimately provide early and more accurate diagnosis.

I don’t have room here to summarize all the results from the Jagust lab, let alone all the other labs doing Alzheimer’s research. But I must say that I’m optimistic given the recent progress they have made in understanding the disease. There are also many clinical trials underway for new Alzheimer’s drugs, including ones that hope to stop cognitive deterioration instead of just reducing symptoms. I’m encouraged but I still tell my friends who are doing the research that they need to find a cure within the next 10 years, because I do not want to suffer through this frightening disease like my mother did.

PET Imaging — Not for Cats or Dogs

PET ring drawingAs a medical imaging researcher, I notice when medical imaging technologies are mentioned by popular news media or medical-themed television shows. Lately I’ve been seeing PET imaging mentioned more frequently, including on TV shows like House and Grey’s Anatomy. This probably just reflects the fact that dramatically increasing numbers of PET scans are being performed in real life in clinics and hospitals. So what is PET imaging? Funny that you ask, because I just happen to do research in this field.

In this context, PET stands for Positron Emission Tomography. During a PET scan, a trace amount of biologically-active, radioactive drug is injected into the patient’s vein. The drug localizes somewhere in the patient, depending on the metabolic properties of the selected drug. The drug then emits a positron (anti-particle of the electron), and the positron annihilates with an electron in the patient’s body. The resulting energy forms gamma ray pairs that pass through the patient and are detected by the PET scanner. These detected gamma ray signals are used to create a 3-D volumetric image or picture of the drug’s concentration in the body.

PET imaging technology is unique because it images a patient’s metabolism, whereas most other medical imaging techniques measure anatomical structure. For example, X-ray CT or MRI scans can be used to identify a tumor because they show the patient’s anatomy in detail. However, PET imaging can identify if the tumor is benign or cancerous, by measuring whether or not the tumor takes up the radioactive drug. In reality, you’d really like to know both though — detailed anatomical structure and metabolic function. Recent work has demonstrated the increased clinical diagnostic value of fusing imaging technologies based on function (e.g., PET, SPECT or functional MRI) with those based on structure (e.g., CT, MRI, or ultrasound). As a result, PET and CT scanners are now typically combined into a single gantry system, so that images can be taken from both devices sequentially during a single procedure.

Since PET measures metabolism instead of anatomical structure, it is mostly used to image organs whose size or shape does not indicate whether they are functioning properly, such as the brain or heart. It is also used to diagnose diseases that exhibit an abnormal metabolism, such as cancer.

Stay tuned this week when I discuss some Alzheimer’s research that utilizes PET imaging.