Ultrasound diagnostic imaging
By: Dr. Lina Restrepo Giraldo
Physician, Endocrinologist, Laboratorio Clínico Hematológico S.A. Medellín, Colombia.
Published on 19/08/2021
Ultrasound or ultrasonography uses ultrasound (inaudible to the human ear, i.e. greater than 20,000 Hz) to obtain images of many structures of the human body. It is a safe procedure since it does not generate radiation (it does not use X-rays) and is harmless, so it can be used in pregnant women, in whom radiation-based studies (e.g. X-rays, CT scans and scans) are contraindicated(1).
The quality of ultrasound depends on the knowledge and expertise of the sonographer. Among its advantages is the ease with which it can be performed, in a short time and at a lower cost than other imaging studies. In case the patient requires complementary images, the physician may order them according to each individual case (2).
How is an ultrasound performed?
The sonographer spreads a conductive gel on the skin and slides a device, the transducer, over the area to be studied. During the procedure the physician may ask the patient to assist with breathing movements or breathing pauses when needed (2).
The transducer produces sound waves that bounce off the body structures. The images are obtained according to the propagation and reflection (echo) of the sound waves in the tissues in different ways depending on their composition. These data are received back by the transducer and sent to a data processing unit (computer) to be displayed as an image (ultrasound) on a gray scale ranging from black (anechoic) to white (hyperechoic) (Figure 1). The greater the wave amplitude received by the transducer (echoes), the whiter or brighter the image will be (1,3).
Figure 1. Echoes are presented on a gray scale. Liquids such as water, which allow the complete passage of waves (no echoes), are anechoic or appear black in the image, while bones, which reflect all echoes, are hyperechoic or appear whiter (3,4).
What are the limitations of general ultrasound?
Ultrasound waves are disrupted by air or gas. Therefore, ultrasound is not an ideal imaging technique for evaluating air-filled bowel or organs obscured by bowel. Ultrasound is less useful for imaging air-filled lungs, but can be used to detect fluids around or within them. Similarly, ultrasound cannot penetrate bone, but can image bone fractures and observe infection surrounding a bone (4).
Types of ultrasound scans
Abdominal ultrasound is one of the most frequent; it is used to explore abdominal organs such as the gallbladder, liver, biliary tract, kidneys and urinary tract, pancreas and spleen. It also includes the evaluation of the aorta, uterus and ovaries in women and the prostate in men. This examination can be performed of the total abdomen, when it includes all the organs and structures mentioned, or of the upper abdomen, when the pelvic organs are not included in the examination. It can also be performed only of the liver and accessory organs, or of the kidney and urinary tract (2).
Pelvic ultrasound: is used to explore the pelvic organs, mainly the uterus, ovaries and bladder in women and the bladder and prostate in men. It is generally performed transabdominally, that is, by exploring the abdomen. When greater detail of these organs or the surrounding tissues is required, the study is performed with a special transducer, which is previously sterilized (5).
The transducer used in these cases is connected to a probe and is inserted into a natural opening of the body for scanning: into a man's rectum to view the prostate and seminal vesicles ( transrectal ultrasound) and into a woman's vagina to visualize the uterus and ovaries ( transvaginal ultrasound).
Soft tissue ultrasound: it is used to evaluate alterations in:
- Thyroid and parathyroid glands: it is the best test to evaluate the structure of the thyroid, the presence of thyroid nodules and their characteristics.
- Breast ultrasound: allows the evaluation of the characteristics of the breast and the presence of breast lumps.
- Testicular ultrasound
- Ultrasound of other superficial locations: salivary glands, neck lymph nodes, subcutaneous tissue and muscles of upper and lower extremities, abdominal wall, among others (6).
This procedure can also be used as a guide to perform fine needle puncture and aspiration (FNA), cytology or biopsy of the possible alterations found in the study.
Vascular ultrasound: this test uses Doppler ultrasound, a variety of traditional ultrasound, which works by measuring sound waves that reflect off moving objects such as circulating red blood cells. This makes it possible to determine the speed and direction in which blood flows through the blood vessels (2).
It is used to evaluate veins and arteries and their alterations such as dilatations, narrowing or occlusions. The most frequently explored vessels are those of the neck, abdominal aorta, renal and upper and lower limbs. It is also used for the follow-up of vascular grafts and arteriovenous fistulas for hemodialysis and the evaluation of blood flow and portal hypertension (3).
Obstetric ultrasound: used by obstetricians and gynecologists to monitor pregnant women and their unborn babies, as well as to explore the placenta, uterus, cervix and amniotic fluid at different stages of pregnancy (1).
Joint ultrasound: it is used to visualize joint soft tissues such as muscles, cartilage, tendons and their relationship with bones in different locations such as shoulder, knee and hip. It is also used as a guide for a directed puncture to extract fluid or biopsy material from a visualized lesion (1).
Echocardiography: performed by echocardiographic cardiologists to evaluate the structure and function of the heart with its valves and the great vessels that emerge from it (pulmonary artery and aorta). There is a variation known as transesophageal echocardiography in which the transducer is inserted into the esophagus to obtain images of the heart (1).
Interventional ultrasound: in this case ultrasound is used as a guide for diagnostic and therapeutic procedures such as biopsies, cyst aspirations, drainage of liquid collections in the lung, abdomen and soft tissues and techniques for tumor treatment (oncological ablation) (1).
Preparation for the exam
Ultrasound is a safe procedure, with low risk of complications, it is not painful and its duration is approximately 15 to 30 minutes. Ideally, on the day of the ultrasound appointment, the patient should wear loose-fitting clothing for comfort. You may be asked to remove metal objects during the ultrasound, so it is a good idea to leave them at home (2).
The test does not require fasting or special conditions in most cases. For abdominal ultrasounds (total, upper, liver, liver, abdominal aorta, renal arteries and evaluation of blood flow and portal hypertension) an 8-hour fast is recommended.
Additionally, for the total abdominal, urinary tract and transabdominal pelvic (prostate and gynecological) ultrasound procedures, it is necessary to have a full bladder, so you should drink plenty of water (about 6 glasses) two hours before the test and not evacuate the bladder before the examination. On the other hand, for the transvaginal pelvic examination it is necessary to evacuate the bladder (urinate) before the examination and for the transrectal pelvic examination it is necessary to have a liquid diet one day before the examination (2).
In the case of an interventional ultrasound its duration may be longer (between 30 and 90 minutes), even in some procedures may require a period of observation afterwards. If necessary, it can be performed under local anesthesia, analgesia or sedation. For these procedures it is recommended to fast for 6 to 8 hours and not to suspend your medications. If you are taking aspirin or anticoagulants you should ask your treating physician if you can interrupt them temporarily. We recommend that you always verify before your appointment the conditions of the test that has been ordered by your doctor (3).
In the Hematology Department we have an ultrasound service, with a 7.5 MHz to 12.0 MHz high resolution transducer ultrasound scanner, which allows obtaining high quality images and is operated by trained medical personnel.
Get to know the complete ultrasound portfolio and preparation conditions here. Schedule your appointment by calling (604) 352 40 20 or write us at WhatsApp 311 749 7048. Ask if they are included in your policy or prepaid medicine plan.
Bibliography
- American College of Radiology, Radiological Society of North America. General Ultrasound [Internet]. radiologyinfo.org. 2018. Available at: https://www.radiologyinfo.org/en/info/genus.
- Adam A, Dixon A, Gillard J, Schaefer-Prokop C, Grainge R. Grainger & Allison's Diagnostic Radiology: A Textbook of Medical Imaging. 6th ed. Philadelphia, USA: Churchill Livingstone; 2014. 2016 p.
- Borrego R, González R. Basic fundamentals of ultrasound [Internet]. Ultrasound working group. Spanish Society of Pediatric Intensive Care; 2018. Available at: https://secip.com/wp-content/uploads/2018/09/1-FUNDAMENTOS-BASICOS-DE-ECOGRAF%C3%8DA.pdf
- Díaz-Rodríguez N, Garrido-Chamorro R, Castellano-Alarcón J. Methodology and techniques. Ultrasound: physical principles, ultrasound scanners and ultrasound language. Medicina de Familia-SEMERGEN. 2007;33:362-9.
- American College of Radiology, Radiological Society of North America. Ultrasound [Internet]. radiologyinfo.org. 2018. Available at: https://www.radiologyinfo.org/en/ultrasound.
- Girish G, Jacobson J. Ultrasound. In: Imaging for musculoskeletal arthritis and metabolic bone disease. Weissman BN. Philadelphia, USA: Saunders Elsevier; 2009. p. 89-104.
