• shortness of breath
• chest pain or tightness
• previous history or family history of cardiac problems
• follow-up on progression of known disease
• establishment of a baseline for newly diagnosed cardiac patients
• arm/jaw/back pain (less likely)
• assessment of damage from myocardial infarction
• cardiac arrhythmias
• cardiomyopathy
• congestive heart failure staging
• pre-operative evaluations

Women in particular have unusual or atypical symptoms of heart disease and heart attacks. This particular imaging test is especially important for women for proactive cardiac evaluation that will lead to an early intervention when indicated.

The test has three basic components – acquisition of resting images, stress portion of the test, and acquisition of stress images.

The specific imaging agent used for stress testing is a technetium/sestamibi combination. As I explained in a previous blog, technetium is the radioactive component of the imaging dose, which provides the detectable energy. Sestamibi, with the trade name of Cardiolite®, delivers the radioisotope to the target organ or system. In this case, sestamibi is taken up by mitochondria, based on two critical factors, both of which are at the heart of the study (pun intended):

• Blood flow to the region
• Cellular viability

There is another agent available, tetrofosmin with the brand name Myoview®, which has very similar chemical properties to sestamibi, and their imaging protocols are interchangeable. In addition, thallium-201 is the original radiotracer that is not used any longer, due to less favorable timing and energy properties.

For those interested in greater technical detail, here is brief additional information about the mechanism of uptake of both sestamibi and tetrofosmin. Sestamibi uptake is a function of plasma and mitochondrial membrane potentials. Accumulation of tetrofosmin is based on similar mechanism of mitochondrial ability to transduce metabolic energy into electronegative membrane potentials. Mitochondria generate cellular energy and are especially numerous in muscle cells due to their high metabolic needs. This is precisely the reason heart muscle uptake of both imaging agents is much greater than background and is the foundation of nuclear cardiac imaging. Once in mitochondria, neither agent leaves in an appreciable amount of time, thus allowing delayed imaging up to several hours.

Since the uptake is proportionate to blood flow to the heart muscle and viability of cells and their mitochondria, the study addresses both questions. The results provide information on regional blood flow patterns and patency, as well as the health of the heart muscle. This information is particularly important for patients with low risk for heart disease, as it determines their cardiac disease status in a non-invasive manner and allows early intervention if indicated.

Nuclear Stress Test

With several million performed each year, the stress test is probably the most common nuclear imaging procedure performed. Patients can be referred for evaluation of chest pain, shortness of breath, previous or family cardiac history, angina, and many other indications or as a part of pre-operative work up.

Preparation

There are several study protocols and different facilities might have slight variations in patient preparation for the nuclear stress test. The following descriptions describe the most commonly used approaches to the preparation and testing.

Patients should not eat for at least 4-6 hours and should refrain from any caffeine intake for a minimum of 12 hours. Even caffeine-free beverages have enough caffeine to potentially affect the test and should be avoided. The same is true for chocolate and certain classes of medication. Most physicians are aware of these contraindications and provide clear patient instructions. It is always a good idea to call the testing center ahead of time to check specific details. Patients can take their medications the morning of the test with few sips of water. This is very important for blood pressure medications. In case of doubt, bring your medicines with you and check with nuclear medicine staff before taking them. And it is always helpful to bring a written list of medications and their dosages and frequency taken with you.

The test itself takes approximately 2.5 – 3 hours. It is best to wear comfortable, loose clothing, and athletic shoes, especially for those patients that will exercise on a treadmill. Women should wear athletic bras or ones without hooks in the front and underwires.

There are several cardiac imaging test studies (nuclear and non-nuclear):

Exercise Stress Test

• Simple treadmill walking test
• Indication: low risk patients with good to excellent exercise capacity correlated with their age with no prior cardiac history and no EKG changes
• Relatively low sensitivity test and specificity

Cardiolite Rest Test

• Patients are injected with Cardiolite nuclear imaging agent at rest and scanned with an hour
• Indications: active chest pain within 4 hours of onset of symptoms, patients with low cardiac event probability
• Contraindications: no active chest pain, ongoing chest pain longer than 4 hours, known abnormal previous nuclear imaging, cardiac history
• Sensitivity and specificity is good for patients with recent ischemic event with no prior cardiac history

Exercise Stress/Rest with Nuclear Imaging

• Patients receive resting dose of Cardiolite nuclear imaging agent, resting scan, than treadmill exercise test with a second, higher dose of Cardiolite during exercise, and second set of images
• Indications: higher risk patients, baseline EKG abnormalities
• Contraindications: inability to exercise up to 85% of target heart rate (220-age), left bundle branch block, active chest pain, rising troponin levels, severe anemia (non-ESRD patients), abnormal potassium levels, TIA or suspected stroke
• Sensitivity and specificity is very high
• Limitations: insufficient exercise capacity

Pharmacological Stress/Rest Test with Nuclear Imaging

Lexiscan is the most commonly used pharmacological stress agent; Adenoscan, Persantine and Dobutamine are rarely used

• Indications: inability to exercise, left bundle branch block
• Contraindications: caffeine within 12 hours, active wheezing, active chest pain, rising troponin levels, severe anemia (non-ESRD patients), abnormal potassium levels, TIA or suspected stroke
• Sensitivity and specificity is quite high

MUGA  (Multiple Gated Acquisition) Scan

• Specialized type of nuclear imaging
• Very accurate and reproducible in determining strength and size of heart beats as ejection fraction
• Used mostly for evaluation of chemotherapy effect on heart function and to evaluate congestive heart failure
• Sensitive and specific for certain indications

Cardiac Echo

• Specialized type of ultrasound imaging
• Excellent for evaluation of heart anatomy, valves
• Not sensitive or specific for coronary artery disease detection

Stress Cardiac Echo

• Baseline cardiac echo is followed by stress echo following an exercise stress test, typical on a stationary bicycle
• Rarely used

Transesophageal Cardiac Echo

• More involved form that requires sedation and extensive preparation
• The ultrasound transducer is passed into esophagus to image very close to the heart
• Not commonly used, indicated for patients with very thick chest or emphysema

Dobutamine Stress Echo

• Cardiac echo performed during stress test with dobutamine
• Heart rate and blood pressure increase in response to the medication
• Sensitive and specific for evaluating anatomy under induced stress conditions

Based on the cardiac imaging and other relevant tests, the attending physician or cardiologist can determine most appropriate course of treatment or intervention.

* PET and PET/CT (a part of Nuclear Medicine) are also beginning to contribute to diagnostic cardiac imaging. We will discuss the various tests and developments in this modality in a following post.

Role of the pharmaceutical

The pharmaceutical part of a dose is taken up by a target organ or system once injected or ingested. It is processed through a normal metabolic pathway that occurs in the body naturally. Since the action in body is part of what normally occurs, there are no side effects due to the pharmaceuticals. They just follow the normal path through body, without having any noticeable effect.

The active part of the dose accumulates in the target area in normal, functional pattern and or amount. Anything different is considered either suspicious and subject to further evaluation or abnormal, subject to treatment or intervention.

Role of the radioisotope

Medical radioactive isotopes are selected for optimal imaging properties. Those include short half-life, low energy, easy availability, and affordable prices.

Each radioisotope emits certain form of energy that is detected by nuclear medicine cameras. The initial signal is digitized and stored in a computer and can be further processed and manipulated to produce the final image, ready for physician interpretation.

Rest of the dose

As with most medications, there are other components that are inert but help to keep the pharmaceutical in solution form, dissolved, pure, and serve many other functions. Their presence does not affect either the imaging or functional properties of radiopharmaceutical and they are subject to the same strict rules as other medications are.

Sterile physiological saline solution is often added to dilute or otherwise prepare individual patient doses.

Radioisotopes are pure forms of certain radioactive elements that do not have pharmaceutical component. They function alone and produce the desired image directly. A great example is radioactive iodine for thyroid imaging.

Nuclear medicine imaging dose, with few exceptions, consist of a pharmaceutical or active component that targets a specific process in the body. This is chemically linked to one of the several radioisotopes to create the radiopharmaceutical dose.

Most doses are injected into a vein of arm or hand, several forms are ingested, and one is inhaled. None of the radioactive tracers cause any side effects. As with any other imaging using ionizing radiation (such as x-rays or CT), there is a very small risk of increased rate of cancers and potentially other diseases. The chance is minimal and well-studied by FDA and medical community. Our goal is to help our patients, not to expose them to excessive harmful radiation.

There is a number of nuclear medicine studies with various protocols that can vary even across different facilities. But in general, once the patient receives the initial dose, there is a delay before imaging begins for the radiotracer to localize in the system or organ of interest.

Nuclear medicine cameras are large but they are passive detectors and emit no radiation and very little noise. Most imaging is relatively long, from 20 minutes up to several hours. Patients are typically lying down, with pillows, blankets, and knee cushions as needed for their comfort. We also have a variety of music available and patients can bring their CDs or iPods to listen to during imaging. The technologist normally stays with the patient in the imaging room to provide time updates and reassurance as needed.

The one feature of nuclear medicine, unlike most other diagnostic imaging, is that it images physiology rather than anatomy. The discipline is very sensitive in showing how organs or systems work rather than what they look like. This is invaluable diagnostic information that is not available through other imaging. Together with other tests and often anatomical imaging via CT, MRI, or ultrasound, nuclear medicine functional studies provide a critical part of patient’s medical evaluation.

My posts will describe common Nuclear Medicine studies as they are done in our department at a mid-size community teaching hospital in Maryland. Even though different facilities, especially teaching and research ones, might have slightly different protocols, our protocols represent a good sample of the studies. I will strive to mention different ways of doing nuclear medicine studies when the procedures might differ significantly.

Feel free to ask questions as we go over ‘nuts and bolts’ or ‘rays and photons’ of nuclear medicine, this blog is for you and about you, the patients and interested public. The only bad question is the one that remains unasked. Let’s have fun exploring nuclear medicine and learn at the same time.

We are going to delve into the secrets and mysteries of Nuclear Medicine to gain understanding of the imaging discipline and its principles.

Nuclear Medicine Myocardial Perfusion Images

Diagnostic imaging provides a glimpse into the structure and anatomy of our bodies. Knowing what an organ or a system looks like and works can be very valuable for your physician. Many diagnoses are made with the aid of diagnostic imaging studies.

X-Ray

Most of us are familiar with x-rays and had one or many at some point in our lives. This imaging modality is the oldest one; x-ray radiation was first detected by Conrad Roentgen November 8^th, 1895. Patient is placed between a source and detecting medium and briefly exposed to radiation with specific wavelength and energy. The old, familiar x-ray film is not used anymore; x-rays are detected and stored digitally.

Xray image of the heart

CT

CT, CAT scan or computed tomographic imaging by its technical name is a form of three-dimensional x-ray. A number of source/detector pairs is mounted on a circular gantry that spins around the patient. When the system is energized, multiple beams pass through the patient and are detected. The massive amount of data can be manipulated to produce exquisitely detailed 3D images.

CT image of the heart

MRI

MRI uses atomic properties and magnetic field to produce incredibly detailed images of certain tissues and organs. This imaging modality does not produce ionizing radiation and is considered very safe, even in pregnancy.

MRI image of the heart

Ultrasound

Ultrasound employs sound waves and their echo to examine certain organs and tissues. It is also very safe and non-invasive.

Ultrasound image of the heart

And on to nuclear medicine, finally, in the next blog.

As a senior technologist with a 15-year career in Nuclear Medicine, I have heard and seen some glorious misconceptions about our imaging modality. The latest example was just a few days ago when patient was told about swallowing a radioactive chip for a bone scan, I think. Not even close, except the radioactive part.

And how many patients have asked if they will glow in the dark, will their urine or stools glow/change/become green. <G> Radiation only comes from bombs and imaging and is dangerous. Most patients are joking, few seem to be serious. Many also ask if we can speed up the study – nope, cannot do so and will explain why.

The other common, not so funny myth, is whether nuclear medicine causes cancer. There is a small grain of truth to this and we will explore the truth and the science behind it shortly.

Now on to diagnostic imaging in the next blog.

Here are few highlights:

• My next project – blog and industry articles, in cooperation with Mid-Atlantic Imaging Services, Inc. (MAI Services), a company that provides a full range of nuclear medicine gamma camera equipment and service for general nuclear medicine and nuclear cardiology.
• Guest lecturer at the Johns Hopkins Hospital Nuclear Medicine Technology program – the same program I graduated from
• June 2011 – I will be presenting again at the Society of Nuclear Medicine (SNM) annual meeting in SanAntonio, Texas
• November 2009 − Selected as a presenter for Medical Imaging delegation to China; did a presentation on credentialing of radiology nurses for representatives from Chinese Ministry of Health
• June 2009 − Chosen as Speaker/moderator at the Society of Nuclear Medicine annual meeting in Toronto; did a presentation on thyroid cancer and treatment
• June 2009 – Awarded scholarship from the Society of Nuclear Medicine for MS/MBA at JHU

I have also finished MS/MBA in biotechnology from the Johns Hopkins University in August 2010.

Now days I work in a 314-bed, full-service hospital with residency programs in a number of disciplines. Our department has 4 cameras, 9 full-time staffers and several part-timers and PRN technologists. We provide all types of diagnostic nuclear medicine imaging and several therapies as well as rare palliative treatments.