Allergy & Allergy Test
Allergic diseases, are a number of conditions caused by hypersensitivity of the immune system to something in the environment that usually causes little or no problem in most people. These diseases include hay fever, food allergies, atopic dermatitis, allergic asthma, and anaphylaxis. Symptoms may include red eyes, an itchy rash, sneezing, a runny nose, shortness of breath, or swelling. Food intolerances and food poisoning are separate conditions.
Common allergens include pollen and certain food. Metals and other substances may also cause problems. Food, insect stings, and medications are common causes of severe reactions. Their development is due to both genetic and environmental factors. The underlying mechanism involves immunoglobulin E antibodies (IgE), part of the body's immune system, binding to an allergen and then to a receptor on mast cells or basophils where it triggers the release of inflammatory chemicals such as histamine. Diagnosis is typically based on a person's medical history. Further testing of the skin or blood may be useful in certain cases.Positive tests, however, may not mean there is a significant allergy to the substance in question.
Treatments for allergies include avoiding known allergens and the use of medications such as steroids and antihistamines. In severe reactions injectable adrenaline (epinephrine) is recommended. Allergen immunotherapy, which gradually exposes people to larger and larger amounts of allergen, is useful for some types of allergies such as hay fever and reactions to insect bites. Its use in food allergies is unclear.
Many allergens such as dust or pollen are airborne particles. In these cases, symptoms arise in areas in contact with air, such as eyes, nose, and lungs. For instance, allergic rhinitis, also known as hay fever, causes irritation of the nose, sneezing, itching, and redness of the eyes. Inhaled allergens can also lead to increased production of mucus in the lungs, shortness of breath, coughing, and wheezing.
Beside from these ambient allergens, allergic reactions can result from foods, insect stings, and reactions to medications like aspirin and antibiotics such as penicillin. Symptoms of food allergy include abdominal pain, bloating, vomiting, diarrhea, itchy skin, and swelling of the skin during hives. Food allergies rarely cause respiratory (asthmatic) reactions, or rhinitis. Insect stings, food, antibiotics, and certain medicines may produce a systemic allergic response that is also called anaphylaxis; multiple organ systems can be affected, including the digestive system, the respiratory system, and the circulatory system. Depending on the rate of severity, anaphylaxis can include skin reactions, bronchoconstriction, swelling, low blood pressure, coma, and death. This type of reaction can be triggered suddenly, or the onset can be delayed. The nature of anaphylaxis is such that the reaction can seem to be subsiding, but may recur throughout a period of time.
Substances that come into contact with the skin, such as latex, are also common causes of allergic reactions, known as contact dermatitis or eczema. Skin allergies frequently cause rashes, or swelling and inflammation within the skin, in what is known as a "weal and flare" reaction characteristic of hives and angioedema.
With insect stings a large local reaction may occur (an area of skin redness greater than 10 cm in size). It can last one to two days. This reaction may also occur after immunotherapy.
Risk factors :
Include heredity, sex, race, and age, with heredity being by far the most significant. However, there have been recent increases in the incidence of allergic disorders that cannot be explained by genetic factors alone.
Include infectious diseases during early childhood, environmental pollution, allergen levels, and dietary changes.
A wide variety of foods can cause allergic reactions, but 90% of allergic responses to foods are caused by cow's milk, soy, eggs, wheat, peanuts, tree nuts, fish, and shellfish. Milk-protein allergies are most common in children.
Latex can trigger an IgE-mediated cutaneous, respiratory, and systemic reaction. The prevalence of latex allergy is less than one percent. The most prevalent response to latex is an allergic contact dermatitis, a delayed hypersensitive reaction appearing as dry, crusted lesions. This reaction usually lasts 48–96 hours. Sweating or rubbing the area under the glove aggravates the lesions, possibly leading to ulcerations. Anaphylactic reactions occur most often in sensitive patients who have been exposed to a surgeon's latex gloves during abdominal surgery, but other mucosal exposures, such as dental procedures, can also produce systemic reactions.
||Redness and itching of the conjunctiva (allergic conjunctivitis, watery)
||Sneezing, coughing, bronchoconstriction, wheezing and dyspnea, sometimes outright attacks of asthma, in severe cases the airway constricts due to swelling known as laryngeal oedema
||Feeling of fullness, possibly pain, and impaired hearing due to the lack of eustachian tube drainage.
||Rashes, such as eczema and hives (urticaria)
||Abdominal pain, bloating, vomiting, diarrhea
About 10% of people report that they are allergic to penicillin; however, 90% turn out not to be. Serious allergies only occur in about 0.03%.
Toxins interacting with proteins
Another non-food protein reaction, urushiol-induced contact dermatitis, originates after contact with poison ivy, eastern poison oak, western poison oak, or poison sumac
Allergic diseases are strongly familial: identical twins are likely to have the same allergic diseases about 70% of the time; the same allergy occurs about 40% of the time in non-identical twins. Allergic parents are more likely to have allergic children, and those children's allergies are likely to be more severe than those in children of non-allergic parents.
The hygiene hypothesis was developed to explain the observation that hay fever and eczema, both allergic diseases, were less common in children from larger families, which were, it is presumed, exposed to more infectious agents through their siblings, than in children from families with only one child. It is used to explain the increase in allergic diseases that have been seen since industrialization, and the higher incidence of allergic diseases in more developed countries.
Chronic stress can aggravate allergic conditions
Allergy testing can help confirm or rule out allergies. To assess the presence of allergen-specific IgE antibodies, two different methods can be used: a skin prick test, or an allergy blood test. Both methods are recommended, and they have similar diagnostic value.
Skin prick tests and blood tests are equally cost-effective, and health economic evidence shows that both tests were cost-effective compared with no test.
An allergy blood test is quick and simple. Unlike skin-prick testing, a blood test can be performed irrespective of age, skin condition, medication, symptom, disease activity, and pregnancy. Adults and children of any age can take an allergy blood test. For babies and very young children, a single needle stick for allergy blood testing is often more gentle than several skin tests.
A sample of the patient's blood is sent to a laboratory for analysis, and the results are sent back a few days later. Multiple allergens can be detected with a single blood sample. Allergy blood tests are very safe, since the person is not exposed to any allergens during the testing procedure.
Management of allergies typically involves avoiding what triggers the allergy and medications to improve the symptoms. Allergen immunotherapy may be useful for some types of allergies.
Several medications may be used to block the action of allergic mediators, or to prevent activation of cells and degranulation processes. These include antihistamines, glucocorticoids, epinephrine (adrenaline), mast cell stabilizers, and antileukotriene agents are common treatments of allergic diseases. Anti-cholinergics, decongestants, and other compounds thought to impair eosinophil chemotaxis, are also commonly used.
Allergen immunotherapy is useful for environmental allergies, allergies to insect bites, and asthma. Its benefit for food allergies is unclear and thus not recommended. Immunotherapy involves exposing people to larger and larger amounts of allergen in an effort to change the immune system's response.
Meta-analyses have found that injections of allergens under the skin is effective in the treatment in allergic rhinitis in children and in asthma. The benefits may last for years after treatment is stopped. It is generally safe and effective for allergic rhinitis and conjunctivitis, allergic forms of asthma, and stinging insects.
Bone Mineral Density (BMD)
Bone density, or bone mineral density (BMD), is the amount of bone mineral in bone tissue. The concept is of mass of mineral per volume of bone (relating to density in the physics sense), although clinically it is measured by proxy according to optical density per square centimeter of bone surface upon imaging. Bone density measurement is used in clinical medicine as an indirect indicator of osteoporosis and fracture risk. It is measured by a procedure called densitometry. The measurement is painless and non-invasive and involves low radiation exposure. Measurements are most commonly made over the lumbar spine and over the upper part of the hip. The forearm may be scanned if the hip and lumbar spine are not accessible.
There is a statistical association between poor bone density and higher probability of fracture. Fractures of the legs and pelvis due to falls are a significant public health problem, especially in elderly women, leading to much medical cost, inability to live independently and even risk of death. Bone density measurements are used to screen people for osteoporosis risk and to identify those who might benefit from measures to improve bone strength.
Indications for Testing
The following are risk factors for low bone density and primary considerations for the need for a bone density test.
- Females age 65 or older
- Males age 70 or older
- People over age 50 with any of the following:
- previous bone fracture from minor trauma
- rheumatoid arthritis
- low body weight
- a parent with a hip fracture
- Individuals with vertebral abnormalities.
- Individuals receiving, or planning to receive, long-term glucocorticoid (steroid) therapy.
- Individuals with primary hyperparathyroidism.
- Individuals being monitored to assess the response or efficacy of an approved osteoporosis drug therapy.
- Individuals with a history of eating disorders
Other considerations which related to risk of low bone density and the need for a test include smoking habits, drinking habits, the long-term use of corticosteroid drugs, and a vitamin D deficiency.
Types of Tests
DXA is currently the most widely used, but quantitative ultrasound (QUS) has been described as a more cost-effective approach to measure bone density. The DXA test works by measuring a specific bone or bones, usually the spine, hip, and wrist. The density of these bones is then compared with an average index based on age, sex, and size. The resulting comparison is used to determine risk for fractures and the stage of osteoporosis (if any) in an individual.
Average bone mineral density = BMC / W [g/cm2]
- BMC = bone mineral content = g/cm
- W = width at the scanned line
Results are generally scored by two measures, the T-score and the Z-score. Scores indicate the amount one's bone mineral density varies from the mean. Negative scores indicate lower bone density, and positive scores indicate higher.
The T-score is the relevant measure when screening for osteoporosis. It is the bone mineral density (BMD) at the site when compared to the young normal reference mean. It is a comparison of a patient's BMD to that of a healthy 30-year-old. The US standard is to use data for a 30-year-old of the same sex and ethnicity, but the WHO recommends using data for a 30-year-old white female for everyone. Values for 30-year-olds are used in post-menopausal women and men over age 50 because they better predict risk of future fracture. The criteria of the World Health Organization are:
- Normal is a T-score of −1.0 or higher
- Osteopenia is defined as between −1.0 and −2.5
- Osteoporosis is defined as −2.5 or lower, meaning a bone density that is two and a half standard deviations below the mean of a 30-year-old man/woman.
|Hip fractures per 1000 patient-years
||Age > 64
The Z-score is the comparison to the age-matched normal and is usually used in cases of severe osteoporosis. This is the number of standard deviations a patient's BMD differs from the average BMD of their age, sex, and ethnicity. This value is used in premenopausal women, men under the age of 50, and in children. It is most useful when the score is less than 2 standard deviations below this normal. In this setting, it is helpful to scrutinize for coexisting illnesses or treatments that may contribute to osteoporosis such as glucocorticoid therapy, hyperparathyroidism, or alcoholism.
Breast Cancer Screening
Breast cancer is cancer that develops from breast tissue. Signs of breast cancer may include a lump in the breast, a change in breast shape, dimpling of the skin, fluid coming from the nipple, a newly inverted nipple, or a red or scaly patch of skin. In those with distant spread of the disease, there may be bone pain, swollen lymph nodes, shortness of breath, or yellow skin.
It is recommended that screening for Breast Cancer should be done every two years in women 50 to 74 years old.
The medications tamoxifen or raloxifenemay be used in an effort to prevent breast cancer in those who are at high risk of developing it.
Surgical removal of both breasts is another preventative measure in some high risk women.
In those who have been diagnosed with cancer, a number of treatments may be used, including surgery, radiation therapy, chemotherapy, hormonal therapy and targeted therapy.
Types of surgery vary from breast-conserving surgery to mastectomy. Breast reconstruction may take place at the time of surgery or at a later date.
Worldwide, breast cancer is the leading type of cancer in women, accounting for 25% of all cases. In 2012 it resulted in 1.68 million new cases and 522,000 deaths. It is more common in developed countries and is more than 100 times more common in women than in men.
Modifiable risk factors- things that people can change themselves, such as consumption of alcoholic beverages.
Fixed risk factors- things that cannot be changed, such as age and biological sex.
The primary risk factors for breast cancer are being female and older age. Other potential risk factors include genetics,
lack of childbearing or lack of breastfeeding, higher levels of certain hormones, certain dietary patterns, and obesity.
One study indicates that exposure to light pollution is a risk factor for the development of breast cancer.
Smoking tobacco appears to increase the risk of breast cancer, with the greater the amount smoked and the earlier in life that smoking began, the higher the risk.
In those who are long-term smokers, the risk is increased 35% to 50%. A lack of physical activity has been linked to about 10% of cases.
High fat diet, high alcohol intake, and obesity-related high cholesterol levels, dietary iodine deficiency may also play a role.
Genetics is the primary cause of 5–10% of all cases.
Women whose mother was diagnosed before 50 have an increased risk of 1.7 and those whose mother was diagnosed at age 50 or after has an increased risk of 1.4.
Atypical ductal hyperplasia and lobular carcinoma in situ, found in benign breast conditions such as fibrocystic breast changes increases breast cancer risk.
Diabetes mellitus also increases the risk of breast cancer. Autoimmune diseases such as lupus erythematosusincreases the risk for breast cancer.
Early signs of possible breast cancer. Breast cancer showing an inverted nipple, lump, and skin dimpling.
Signs and symptoms :
The first noticeable symptom of breast cancer is typically a lump that feels different from the rest of the breast tissue. More than 80% of breast cancer cases are discovered when the woman feels a lump. The earliest breast cancers are detected by a mammogram. Lumps found in lymph nodes located in the armpits can also indicate breast cancer.
Indications of breast cancer other than a lump may include thickening different from the other breast tissue, one breast becoming larger or lower, a nipple changing position or shape or becoming inverted, skin puckering or dimpling, a rash on or around a nipple, discharge from nipple/s, constant pain in part of the breast or armpit, and swelling beneath the armpit or around the collarbone. Pain ("mastodynia") is an unreliable tool in determining the presence or absence of breast cancer, but may be indicative of other breast health issues.
Inflammatory breast cancer is a particular type of breast cancer which can pose a substantial diagnostic challenge. Symptoms may resemble a breast inflammation and may include itching, pain, swelling, nipple inversion, warmth and redness throughout the breast, as well as an orange-peel texture to the skin referred to as peaud'orange. As inflammatory breast cancer does not present as a lump there can sometimes be a delay in diagnosis.
Another reported symptom complex of breast cancer is Paget's disease of the breast. This syndrome presents as skin changes resembling eczema, such as redness, discoloration, or mild flaking of the nipple skin. As Paget's disease of the breast advances, symptoms may include tingling, itching, increased sensitivity, burning, and pain. There may also be discharge from the nipple. Approximately half of women diagnosed with Paget's disease of the breast also have a lump in the breast.
In rare cases, what initially appears as a fibroadenoma (hard, movable non-cancerous lump) could in fact be a phyllodes tumor. Phyllodes tumors are formed within the stroma (connective tissue) of the breast and contain glandular as well as stromal tissue. Phyllodes tumors are classified on the basis of their appearance under the microscope as benign, borderline, or malignant.
Occasionally, breast cancer presents as metastatic disease—that is, cancer that has spread beyond the original organ. The symptoms caused by metastatic breast cancer will depend on the location of metastasis. Common sites of metastasis include bone, liver, lung and brain. Unexplained weight loss can occasionally signal breast cancer, as can symptoms of fevers or chills. Bone or joint pains can sometimes be manifestations of metastatic breast cancer, as can jaundice or neurological symptoms.
These symptoms are called non-specific, meaning they could be manifestations of many other illnesses.
Fewer than 20% of lumps are cancerous, and benign breast diseases such as mastitis and fibroadenoma of the breast are more common causes of breast disorder symptoms.
Mammography is a common screening method, since it is relatively fast and widely available in developed countries.
Medical ultrasonography is a diagnostic aid to mammography. Adding ultrasonography testing for women with dense breast tissue increases the detection of breast cancer.
Magnetic resonance imaging(MRI) :
Magnetic resonance imaging (MRI) has been shown to detect cancers not visible on mammograms. A negative MRI can rule out the presence of cancer to a high degree of certainty, making it an excellent tool for screening in patients at high genetic risk or radiographically dense breasts, and for pre-treatment staging where the extent of disease is difficult to determine on mammography and ultrasound. MRI can diagnose benign proliferative change, fibroadenomas, and other common benign findings at a glance, often eliminating the need for costly and unnecessary biopsies or surgical procedures. The spatial and temporal resolution of breast MRI has increased markedly in recent years, making it possible to detect or rule out the presence of small in situ cancers, including ductal carcinoma in situ.
Breast cancer is usually treated with surgery, which may be followed by chemotherapy or radiation therapy, or both.
An Echocardiogramat Chandan Hospital is a sonogram of the heart. Echocardiography uses standard two-dimensional,
three-dimensional, and Doppler ultrasound to create images of the heart.
Echocardiography has become routinely used in the diagnosis, management, and follow-up of patients with any suspected or known heart diseases.
It is one of the most widely used diagnostic tests in cardiology.
It can provide a wealth of helpful information, including the size and shape of the heart (internal chamber size quantification), pumping capacity, and the location and extent of any tissue damage.
An echocardiogram can also give physicians other estimates of heart function, such as a calculation of the cardiac output, ejection fraction, and diastolic function (how well the heart relaxes).
Echocardiography can help detect cardiomyopathies, such as hypertrophic cardiomyopathy, dilated cardiomyopathy, and many others.
The use of stress echocardiography may also help determine whether any chest pain or associated symptoms are related to heart disease.
The biggest advantage to echocardiography is that it is not invasive (does not involve breaking the skin or entering body cavities) and has no known risks or side effects.
Not only can an echocardiogram create ultrasound images of heart structures, but it can also produce accurate assessment of the blood flowing through the heart by Doppler echocardiography, using pulsed- or continuous-wave Doppler ultrasound.
This allows assessment of both normal and abnormal blood flow through the heart.
Color Doppler, as well as spectral Doppler, is used to visualize any abnormal communications between the left and right sides of the heart, any leaking of blood through the valves (valvular regurgitation), and estimate how well the valves open (or do not open in the case of valvular stenosis). The Doppler technique can also be used for tissue motion and velocity measurement, by tissue Doppler echocardiography.
How Safe Is Echocardiography?
It is absolutely safe. There are no known risks of the ultrasound in this type of testing.
Medical Uses :
Echocardiography is a significant tool in providing the physician important information about heart on the following :
- Size of the chambers, volume and the thickness of the walls
- Pumping function, if it is normal or reduced to a mild/severe degree
- Valve function – structure, thickness and movement of heart’s valves
- Volume status as low blood pressure may occur as a result of poor heart function
- Pericardial effusion (fluid in the pericardium and the sac that surrounds the heart), congenital heart disease, blood clots or tumours, abnormal elevation of pressure within the lungs etc.
Trans-Thoracic Echocardiogram :
A standard echocardiogram is also known as a transthoracic echocardiogram, or cardiac ultrasound.
In this case, the echocardiography transducer (or probe) is placed on the chest wall (or thorax) of the subject, and images are taken through the chest wall.
This is a noninvasive, highly accurate, and quick assessment of the overall health of the heart.
Trans-Esophageal Echocardiogram :
This is an alternative way to perform an echocardiogram.
A specialized probe containing an ultrasound transducer at its tip is passed into the patient's esophagus.
This allows image and Doppler evaluation from a location directly behind the heart. This is known as a transesophageal echocardiogram.
Transesophageal echocardiograms are most often used when transthoracic images are suboptimal and when a more clear and precise image is needed for assessment.
Stress Echocardiography :
A stress echocardiogram, also known as a stress echo, uses ultrasound imaging of the heart to assess the wall motion in response to physical stress.
First, images of the heart are taken "at rest" to acquire a baseline of the patient's wall motion at a resting heart rate.
The patient then walks on a treadmill or uses another exercise modality to increase the heart rate to his or her target heart rate,
or 85% of the age-predicted maximum heart rate (220 − patient's age). Finally, images of the heart are taken "at stress" to assess wall motion at the peak heart rate.
A stress echo assesses wall motion of the heart; it does not, however, create an image of the coronary arteries directly.
Ischemia of one or more coronary arteries could cause a wall motion abnormality, which could indicate coronary artery disease.
The gold standard test to directly create an image of the coronary arteries and directly assess for stenosis or occlusion is a cardiac catheterization.
A stress echo is not invasive and is performed in the presence of a licensed medical professional, such as a cardiologist, and a cardiac sonographer.
Three-Dimensional Echocardiography :
Three-dimensional echocardiogram of a heart viewed from the apex Three-dimensional echocardiography (also known as four-dimensional echocardiography when the picture is moving)
is now possible, using a matrix array ultrasound probe and an appropriate processing system.
This enables detailed anatomical assessment of cardiac pathology, particularly valvular defects, and cardiomyopathies.
The ability to slice the virtual heart in infinite planes in an anatomically appropriate manner and to reconstruct
three-dimensional images of anatomic structures make it unique for the understanding of the congenitally malformed heart.
Real-time three-dimensional echocardiography can be used to guide the location of bioptomes during right ventricular endomyocardial biopsies,
placement of catheter-delivered valvular devices, and in many other intraoperative assessments.
Contrast Echocardiography :
Contrast echocardiography, or contrast-enhanced ultrasound is the addition of an ultrasound contrast medium, or imaging agent, to traditional ultrasonography.
The ultrasound contrast is made up of tiny microbubbles filled with a gas core and protein shell. This allows the microbubbles to circulate through
the cardiovascular system and return the ultrasound waves, creating a highly reflective image.
There are multiple applications in which contrast-enhanced ultrasound can be useful.
The most commonly used application is in the enhancement of LV endocardial borders for assessment of global and regional systolic function.
Contrast may also be used to enhance visualization of wall thickening during stress echocardiography, for the assessment of LV thrombus,
or for the assessment of other masses in the heart. Contrast echocardiography has also been used to assess blood perfusion
throughout myocardium in the case of coronary artery disease.
Magnetic Resonance Imaging(MRI)
Magnetic resonance imaging is a medical imaging technique used in radiology to form pictures of the anatomy and the physiological processes of the body in both health and disease.
MRI scanners use strong magnetic fields, electric field gradients, and radio waves to generate images of the organs in the body.
MRI does not involve X-rays and the use of ionizing radiation, which distinguishes it from CT or CAT scans. Magnetic resonance imaging is a medical application of nuclear magnetic resonance (NMR).
NMR can also be used for imaging in other NMR applications such as NMR spectroscopy.
While the hazards of X-rays are now well-controlled in most medical contexts, MRI may still be seen as a better choice than CT.
MRI is widely used in hospitals and clinics for medical diagnosis, staging of disease and follow-up without exposing the body to radiation. However, MRI may often yield different diagnostic information compared with CT.
There may be risks and discomfort associated with MRI scans. Compared with CT scans, MRI scans typically take longer and are louder, and they usually need the subject to enter a narrow, confining tube.
In addition, people with some medical implants or other non-removable metal inside the body may be unable to undergo an MRIexamination safely.
MRI has a wide range of applications in medical diagnosis and more than 25,000 scanners are estimated to be in use worldwide. MRI affects diagnosis and treatment in many specialties although the effect on improved health outcomes is uncertain.
MRI is the investigation of choice in the preoperative staging of rectal and prostate cancer and, has a role in the diagnosis, staging, and follow-up of other tumors.
MRI is the investigative tool of choice for neurological cancers, as it has better resolution than CT and offers better visualization of the posterior fossa. The contrast provided between grey and white matter makes MRI the best choice for many conditions of the central nervous system, including demyelinating diseases, dementia, cerebrovascular disease, infectious diseases, and epilepsy. Since many images are taken milliseconds apart, it shows how the brain responds to different stimuli, enabling researchers to study both the functional and structural brain abnormalities in psychological disorders. MRI also is used in guided stereotactic surgery and radiosurgery for treatment of intracranial tumors, arteriovenous malformations, and other surgically treatable conditions using a device known as the N-localizer.
Cardiac MRI is complementary to other imaging techniques, such as echocardiography, cardiac CT, and nuclear medicine. Its applications include assessment of myocardial ischemia and viability, cardiomyopathies, myocarditis, iron overload, vascular diseases, and congenital heart disease.
Applications in the musculoskeletal system include spinal imaging, assessment of joint disease, and soft tissue tumors.
Liver and gastrointestinal :
Hepatobiliary MR is used to detect and characterize lesions of the liver, pancreas, and bile ducts. Focal or diffuse disorders of the liver may be evaluated using diffusion-weighted, opposed-phase imaging, and dynamic contrast enhancement sequences. Extracellular contrast agents are used widely in liver MRI and newer hepatobiliary contrast agents also provide the opportunity to perform functional biliary imaging. Anatomical imaging of the bile ducts is achieved by using a heavily T2-weighted sequence in magnetic resonance cholangiopancreatography (MRCP). Functional imaging of the pancreas is performed following administration of secretin. MR enterography provides non-invasive assessment of inflammatory bowel disease and small bowel tumors. MR-colonography may play a role in the detection of large polyps in patients at increased risk of colorectal cancer.
Magnetic resonance angiography (MRA) generates pictures of the arteries to evaluate them for stenosis (abnormal narrowing) or aneurysms (vessel wall dilatations, at risk of rupture). MRA is often used to evaluate the arteries of the neck and brain, the thoracic and abdominal aorta, the renal arteries, and the legs (called a "run-off"). A variety of techniques can be used to generate the pictures, such as administration of a paramagnetic contrast agent (gadolinium) or using a technique known as "flow-related enhancement" (e.g., 2D and 3D time-of-flight sequences), where most of the signal on an image is due to blood that recently moved into that plane (see also FLASH MRI). Techniques involving phase accumulation (known as phase contrast angiography) can also be used to generate flow velocity maps easily and accurately. Magnetic resonance venography (MRV) is a similar procedure that is used to image veins. In this method, the tissue is now excited inferiorly, while the signal is gathered in the plane immediately superior to the excitation plane—thus imaging the venous blood that recently moved from the excited plane.