Ultrasound

Imaging In Obstetrics and Gynaecology

The increasing complexity of diagnostic radiology provides a challenge to radiologists

"Magnetic resonance is now emerging as a complementary imaging modality in the field of foetal assessment and in the evaluation of maternal medical problems during pregnancy" - Dr Pankaj Desai Consultant Ob-Gyn Specialist Janani Maternity Hospital Baroda

Obstetrics (science of pregnancy and childbirth) and gynaecology (science of disease of female reproductive tract) are approached differently as regards using imaging science tools are concerned. Obstetrics posed a totally unique challenge in the medical science as regards imaging is concerned. One side was the acute need to know what was happening in the pregnant uterus. On the other side was the risk of birth defects in the unborn child due to conventional imaging technique - the X-rays. Amidst this, the biggest blessing was ultrasonography.

Routine obstetric sonography has also become a social occurrence and an expectation in India. The obstetric sonographic examination is attractive in a way that is uncharacteristic of other medical events. Expectant mothers by and large perceive the sonogram of their foetus as a helpful experience. They hardly ever ask their obstetricians if they have to have a sonogram, they ask when it will be planned. It is extremely common to provide sonographic images to the parents and even provide CDs and videotapes of the examination. In India, most of the times patients show up for their examination accompanied by their husbands.

What is Ultrasonography?

Ultrasonography is a technique that uses high-frequency audio waves to actually see muscles, organs, and other things inside the human body. It makes doing so fairly simple and allows doctors to inspect the body internally without harming it. Basically it has a computer and a probe. The probe releases ultrasonic waves to the target in the patient and receives them after they are echoed back from the targeted tissue or organ. The computer converts these sound echoes into light signals which form an image on the screen. The sound frequency used here is above the limits for which the human ears are programmed to listen. So this sound is not audible to us. Situations where an obstetrician would like to do a sonography are tabulated. ( See Box).

How is the Procedure Performed?

For most ultrasound exams (scans performed per-abdomen), the patient is placed lying face-up on an examination table that can be tilted or moved. A clear water-based gel is applied to the area of the body being studied to assist the transducer or the probe make secure contact with the body and remove air pockets between the transducer and the skin touched. The sonographer (ultrasound technologist) or radiologist then sweeps it over the area of importance.

Sometimes, the sonologist determines that a transvaginal scan needs to be performed. This technique often provides improved, more detailed images of the uterus and ovaries. This method of scanning is especially useful in early pregnancy. Transvaginal ultrasound is performed very much like a gynaecologic exam and involves the insertion of the transducer into the vagina after the patient empties her bladder. The tip of the transducer is smaller than the standard speculum used when performing a routine gynecological examination. A protective cover is placed over the transducer, lubricated with a small amount of gel, and then inserted into the vagina. Only two to three inches of the transducer end are inserted into the vagina. This ultrasound examination is usually completed within 30 minutes.

How Safe Is Sonography?

Current evidence indicates that diagnostic ultrasound is harmless for the unborn child, not like radiographs, which employ ionising radiations. While the benefits of medical ultrasound prevail over any risks, vanity uses such as making 3D ultrasound movies without a doctor's recommendation is clearly uncalled for and generates an unknown risk to a developing foetus. Clinical guidelines recommend against the non-medical use of foetal ultrasound.

What Sonography Doesn't Show?

Obstetric ultrasound cannot make out all foetal abnormalities. As a result, when there are clinical or laboratory doubts for a likely abnormality, a pregnant woman may have to undergo non-radiologic testing such as amniocentesis (the assessment of fluid taken from the sac around the foetus) or chorionic villus sampling (evaluation of placental tissue) to determine the wellbeing of the foetus.

Role of Other Imaging Technologies like MRI and CAT scan

Ultrasonography remains the imaging modality of choice for the evaluation of a pregnant mother and her foetus. It's safe for both parties, is relatively inexpensive, allows real-time imaging, doesn't involve ionising radiation and is readily available. There are limitations, however, including a small field of view, limited soft-tissue acoustic contrast and beam attenuation by adipose tissue in large patients. With respect to foetal evaluation, ultrasonography can be limited by poor image quality in excess fluid around the foetus (oligohydramnios), limited visualisation of the hind of the skull (posterior fossa) after 33 weeks' of pregnancy and limitations in assessing complex foetal anomalies, particularly when scanning late in gestation. Recently, MR has been used to detect placental abnormalities particularly deeply attachments (placenta accreta).

Magnetic Resonance

Magnetic resonance is now emerging as a complementary imaging modality in the field of foetal assessment and in the evaluation of maternal medical problems during pregnancy. During the early 1990s, foetal Magnetic resonance imaging was revolutionised by the development of 'ultrafast' imaging methods, effectively freezing physiologic movement of the foetus and allowing quality imaging with no invasive interventions.

Safety issues with MRI

The contrast agents commonly used in MRI are gadolinium and manganese. These are rare earth metals that are used because of their reactive properties to magnetic fields. These reactions further enhance scanning for abnormalities. However, the presence of these metals in the placenta-blood barrier within minutes of an injection of the contrast medium, coupled with the lack of conclusive evidence of the removal of the medium from the foetal environment, has raised concerns of their long-term affect on the foetus.

Besides, the concerns of using certain contrast media, there are questions about the safety of the foetus due to the heat that is created in the mother's body as a result of the presence of magnetic fields and radio frequencies. While the theory that this generated heat may potentially pose some risk of tissue damage in the foetus, there are currently no proven cases of such. However, MRI is not commonly recommended during pregnancy to avoid any possible complications during this crucial phase of natal development.

What about CAT Scan?

This imaging procedure called a Computed Axial Tomography scan. A CAT scan procedure uses a computer to combine several X-ray images to produce cross-sectional and three-dimensional images of internal organs and other structures. A CAT scan involves exposure to radiation at levels slightly higher than normal X-rays. The effective radiation dose from this procedure is about the same the average person receives from background radiation from the sun in three years. However, rarely, the benefit of receiving an accurate diagnosis may outweigh the risk associated with radiation exposure. It is currently believed that no single diagnostic X-ray has a radiation dose significant enough to cause adverse affects in a developing embryo or foetus. However, in general, CAT scans are not recommended during pregnancy unless the benefits of the CAT scan clearly outweigh the potential risk.

Current Status of Imaging Technologies

Imaging in gynaecology differs from obstetrics on one critical point and that is the absence of the foetus and related safety issues. Ultrasound, computer tomography, and magnetic resonance are predominant imaging technologies in the diagnosis of various gynecological diseases and tumors. Imaging is required in infertility, in the diagnosis of female reproductive tract anomalies and in gynecological oncology. Ultrasound is the first-line imaging method for differentiation between benign and malignant adnexal masses and for making a specific diagnosis in adnexal tumors (e.g. dermoid cyst, endometrioma, hemorrhagic corpus luteum, etc.), for diagnosing intracavitary uterine pathology in women with bleeding problems, and for confirming or refuting pelvic pathology in women with pelvic pain. Magnetic resonance imaging can have a role as a secondary test in different gynecological conditions like adenomyosis, 'deep endometriosis' and the like.

As regards gynaecological cancers these imaging techniques may be used to assist in diagnosis, staging, and follow-up of oncology patients. The increasing complexity of diagnostic radiology provides a challenge to radiologists and oncologists to use these tools in a clinically efficient and cost-effective manner. The ultimate goal is to offer a safe and effective examination that provides clinically relevant information for the management of an individual patient. Currently ultrasound, computed tomography, Magnetic Resonance Imaging (MRI) and Positron Emission Tomography (PET) are being used to evaluate patients with gynaecological malignancies. MRI can play a role in detecting the extent of disease and helps in local staging of gynaecologic tumours. CT can be used to detect extrapelvic disease and PET-CT can assist in detecting distant metastatic disease in order to select appropriate surgical candidates.

Acute pelvic pain may be the manifestation of various gynaecologic and non-gynaecologic disorders. Apart of clinical examination and laboratory tests, an ultrasound examination is very efficient for diagnosing the cause of acute pelvic pain. Still, it is user-dependent and requires considerable experience in order to perform it reliably. Ruptured ectopic (outside the uterus) pregnancy, inflammation of the tubes and bleeding in cysts arising from ovaries are three most commonly diagnosed gynaecologic conditions presenting as an acute pain. Pelvic inflammatory disease may be ultrasonically presented with numerous signs on ultra sonography. Color Doppler ultrasound contributes to more accurate diagnosis of this entity since it enables differentiation between acute and chronic stages. Pelvic congestion syndrome is another condition that can cause an attack of acute pelvic pain. It is usually consequence of dilation of blood vessels (venous plexuses, arteries or both systems). By switching color Doppler, gynaecologist can differentiate causes of pelvic congestion syndrome, corpus luteum cysts and leiomyomas are another cause of pelvic pain during pregnancy, which can be correctly diagnosed by ultrasound.

In closing, imaging technologies are very important and easily available tools which can efficiently recognise patients with diseased conditions of different origins in gynaecology.

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