Updated: Feb 18

Your doctor has just recommended that you have a diagnostic imaging procedure to help diagnose or manage a disease condition. Not knowing what to expect makes the experience even more daunting. We're here to provide answers to your diagnostic imaging questions.

Following are answers to the most-frequently asked questions about diagnostic procedures.

What is Nuclear Medicine?

Nuclear Medicine is an advanced imaging modality that uses radiopharmaceuticals to acquire images of organs of the body. Unlike X-rays and CT's, the nuclear gamma camera does not emit radiation. Nuclear medicine studies can be performed on virtually every organ of the body. One of the most common uses of nuclear medicine is in assessing cardiac disease. Other very common uses are in diagnosis of pulmonary embolism for patients who are allergic to intravenous CT contrast, assessment of gall bladder disease, bone metastases, infection, gastro-paresis and thyroid disease.


Most facilities will contact you prior to the scheduled study date with instructions for any necessary preparations. As a general rule of thumb, exams that involve the stomach or gastro-intestinal system require that you do not eat after midnight prior to the day of the procedure. Nuclear stress tests also require that you do not eat or drink anything at least 6 to 8 hours prior to exam. Depending on the specific method of stress, you may also be required to be off some blood pressure medications. Be sure to speak with your physician to receive instructions regarding medications.

For thyroid exams, contact the facility for specific instructions on how long to be off your thyroid medication.

Nuclear medicine procedures are generally not encouraged for pregnant patients, unless absolutely necessary. The imaging facility will usually reduce the radiopharmaceutical dose to minimize exposure to the fetus. If you are breast-feeding, let the technologist know prior to starting the procedure.

What to expect

A trace amount of radioactive material will be injected in the vein. It then travels through the bloodstream to the organ that needs to be imaged. For thyroid and gastric exams, the radiopharmaceutical is administered orally. The tracers emit a pattern of rays representing the organ size, shape and function. The rays are detected by a gamma camera, producing a characteristic image on a computer screen. The images are transferred to a work station where the technologist uses processing software to convert them to a format presented to the radiologist for review and interpretation.

Most nuclear medicine procedures are performed with a radioisotope called Technetium, which has a half life of 6hrs. This means that half the administered dose is out of the body in 6 hours and almost all is gone in 24 hours. When other higher energy isotopes are used, you will be given relevant special instructions that apply to those specific radioisotopes.

What is Ultrasound?

Ultrasound uses sound waves to produce images of organs and tissues in the body. Ultrasound exams do not use radiation. Transducers are placed over the organ of interest in order to examine the organs. As the ultrasound waves penetrate the body, they are reflected back to the transducer by the internal organs. This process produces echoes which can be very loud. The resulting information are converted into images of the organ being examined.


Some ultrasound exams require that you do not eat or drink anything after midnight prior to the day of your exam. Some other exams require you to drink a lot of fluid to fill up your bladder. Be sure to get specific instructions from the imaging facility staff prior to the day of your exam.

What to expect

To perform an ultrasound, a transmission gel is spread on the area of the body to be examined. The transducer is moved slowly over the organ or area of interest, producing a sensation of pressure on the patient's skin. Different transducers are used, depending on the part of the body being imaged. Ultrasound images are displayed on a monitor similar to a television screen. The Sonographer creates save screens of notable images that best show the anatomy or pathology in question. These images are then formatted and presented to the radiologist for review and interpretation. Many biopsies, especially breast are ultrasound-guided.

What is MRI (Magnetic Resonance Imaging)?

Magnetic resonance imaging is a diagnostic tool that uses electromagnetic radio waves. MRI does not use radiation. The images are displayed in slices just like you would get with a CT scan. MRI images show greater contrast between the different types of body tissues. MRI is very useful for looking at details of the head, neck, spine, muscles, joints and bones.


Most MRI exams do not require special preparation, unless instructed otherwise by the imaging facility. Generally, jewelry, hair clips, watches, coins, keys and any other metal objects should not be taken into the MRI imaging room. It is also advised not to take credit cards and ATM cards into the MRI imaging room as the magnet will erase the magnetic codes on the cards. Patients with metallic or electronic implants, pacemakers or aneurysm clips are advised to alert the imaging facility staff before scheduling the study. MRI may adversely affect these items.

What to expect

During MRI examination, the patient is asked to stay still on a padded table for the duration of the study. MRI exams typically last between 30 to 90 minutes, depending on the area of the body being scanned. The area to be imaged is positioned on the magnet. The MRI technologist maintains contact with the patient throughout the examination. The radio waves used for MRI's produce noise. Most MRI imaging suites have a music system that patients can listen to during the exam. Patients are also encouraged to bring a favorite CD when coming in for appointments.

Is contrast used for MRI exams?

Some MRI examinations require the use of non-iodine contrast injected in the vein. Contrast media increases the sensitivity of the examination and helps provide more detail information that may not visible without contrast. The decision to use contrast will be made by the referring physician and/or supervising radiologist.

What is a CT(CAT) Scan?

Computed Tomography is an advanced imaging modality that produces cross-sectional images (slices) of the body. It is highly sensitive and is able to reveal internal anatomy and detect extremely small lesions that cannot be seen on plain X-rays. The CT scanner rotates 360 degrees around the patient using X-ray tubes. The CT technologist processes the images obtained into slices for display on a computer monitor.

CT angiography (CTA) is considered the gold standard for detecting pulmonary embolism. Other uses of CT include coronary calcium scoring, cancer diagnosis and follow-up, diagnosis of other diseases of the Head, Neck, chest, abdomen and Pelvis. CT is very widely used in biopsies.


Some CT exams require that you do not eat or drink anything after midnight prior to the day of your exam. Be sure to contact imaging facility staff for specific instructions for the scan you are scheduled to have prior to the exam day.

What to expect

During the scan, the patient is asked to lie still on a padded table. Most CT scans take 5 to 20 minutes, depending on the area of the body being scanned. The table slides backward or forward every few seconds as needed to acquire the images. The technologist processes the images and puts them in a special format for the radiologist to review. CT is very sensitive to breathing or motion, so it is very important to follow the technologist's instructions during the procedure to ensure that diagnostic-grade images are obtained.

Different contrast materials are used, depending on the reason for the study . Intravenous contrast is often used . If you are allergic to iodine or if you have had a reaction to intravenous contrast in the past, be sure to notify the facility staff when making the appointment.

Oral contrast is usually given for CT scans that include the abdomen and pelvis. For CT examinations involving oral contrast, the patient is advised to arrive 30 minutes to 1 hour before scan time to allow for time to drink the contrast. Some CT exams may combine oral and intravenous contrast depending on the clinical indication for the exam.

What is Mammography?

Mammography is a medical imaging technique that uses low-dose x-ray to acquire images of the breast. There have been advances in mammography techniques that have made it possible to better visualize breast tissue. These techniques include digital mammography, Computer-aided detection and breast tomosynthesis.

Digital mammography: Digital Mammography is also called full-field digital mammography (FFDM). In this technique, the x-ray film is replaced by solid-state detectors that convert x-rays into electrical signals. The electrical signals are used to produce images of the breast which can be seen on a computer screen or printed on film.

Computer-aided detection (CAD): CAD technique uses a digitized mammographic image which can be obtained from either a conventional mammogram or a digitally acquired mammogram. The CAD software is then used to search for abnormal areas of density, mass, or calcification that may indicate the presence of cancer. Further analyses is recommended for areas identified with CAD.

Breast Tomosynthesis: In Breast Tomosynthesis, also called three-dimensional (3-D) breast imaging, the x-ray tube moves in an arc over the breast during the exposure. This produces a series of thin slices through the breast that makes it possible to better visualize breast tissue. This technique improves detection of cancer and has helped to reduce the number of patients brought back for additional imaging.


Do not use powder, deodorant, lotion or perfume the day of the mammogram.

What to Expect

During a mammogram, you will feel considerable pressure on your breast as it is squeezed by the compression paddle. To minimize pain and sensitivity, it is best not to schedule your mammogram for the week before your period since the breasts tend to be tender during this time. A good time to have a mammogram is one week following your period. Be sure to inform your doctor or mammographer if there is any possibility that you are pregnant.

What is a Bone Density Scan?

Bone densitometry is also known as Dual-Energy X-ray Absorptiometry or DEXA. It is used to measure and monitor changes in bone mineral density. Gradual loss of density weakens the bones and over time may result in fractures. This condition is called osteoporosis. Bone densitometry can estimate whether or not an individual has osteoporosis, as well as the risk for developing the disease. Factors that affect development of osteoporosis include family history and dietary habits and lifestyle.


There is no special preparation for a bone density scan.

What to Expect

Having a bone density test done is a fairly quick process and there are no special preparations. The patient is asked to lie down on the scan table and the x-ray arm scans over specific bones, usually the spine, hip and wrist. There is standardized data regarding known index based on age, gender and size. The density measurements recorded are compared with the standardized data. The results help to assess the risk for fractures. If the individual already has osteoporosis, the results can help stage the disease.

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