It’s not difficult to define the “difficult-to-image patient.” While large patients are usually the first to spring to mind, high-risk obstetrics, ovarian cancer patients, transplant candidates and combative patients pose increased imaging obstacles for sonographers and physicians alike. But the latest iteration of ultrasound systems are easing the barriers to imaging a wide array of challenging patient conditions through improved harmonics, compound imaging and automated processes.
High-risk patients = complicated issues
The practice of Minnesota Perinatal Physicians in the Allina Health System in Minneapolis and St. Paul focuses on high-risk obstetrics, says Medical Director Manny Gaziano, MD. Ultrasound is key to the practice because they serve as a referral site for obstetricians and radiologists for maternal and fetal images.
Gaziano reports that their Philips Medical Systems iU22 ultrasound system has improved their ability to scan these complicated patients. He sees a combination of the skill of the sonographer coupled with patience and excellent equipment as essential. Some high-risk women are positioned on their sides to image through their “flank” rather than employing standard abdominal views. Or they may use transvaginal ultrasound to obtain clear images of a fetus early in pregnancy. The choice of transducer is another aspect to this specialized field, such as a transvaginal probe in this case.
While one type of challenge involves imaging large women, other “difficult to image” categories include pregnant women with decreased amniotic fluid that occurs either with ruptured membranes or if there is an intrinsic fetal problem such as kidney abnormalities. Additional imaging complications arise from fetal positions, or when the placenta is attached to the front wall of the uterus. Forty percent of the women they image have uterine tumors that complicate the imaging process, Graziano says.
Color Doppler is helpful to look for areas that are difficult to image such as the fetal kidney, he explains. If they want to make sure that the fetus has a kidney, they may not be able to determine its presence on a 2D image. Using color power Doppler imaging, based on the flow of red blood cells, enables them to see arterial blood flow to the kidneys thereby ascertaining that a kidney is present.
“Features like adjusting the gain [amplitude of the soundwave] automatically and adjusting harmonics [the balance of the frequency] automatically, and the penetration help us in scanning,” Graziano says. “There are other kinds of automation from the computer that this system gives us to optimize the images.” Although they have very skilled sonographers and physicians, he says it is helpful to have some automatic functionality to save time while improving the image.
Minnesota Perinatal Physicians has begun using the 3D capabilities of this system to identify fetal abnormalities such as cleft lip and palate, abdominal wall defects such as oomphalocoeles or spinal anomalies such as spina bifida.
Gaziano’s particular area of interest involves women who have had a Cesarean section to deliver a previous baby. When a woman has a C-section, she forms a scar, he explains. If she becomes pregnant subsequently and the placenta implants over the scar, that placenta tends to invade maternal tissues and at the time of birth it can cause a major risk of hemorrhage, necessitating hysterectomy or massive blood transfusions.
“It is helpful for us to magnify the area of interest into the scar and then use very precise color settings to show us the tongues of blood flow that go where they should not go,” Gaziano concludes. These imaging scans signal the need for the mother to be delivered in a high-risk perinatal center and prepare the team for possible problems.
Complex differential diagnoses
Michael Crade, MD, medical director of Ultrasonix (a division of Pediatrix Corp.) in Long Beach, Calif., describes their private office practice that performs ultrasound studies primarily for gynecologic patients. They use a GE Healthcare Voluson 730 ultrasound to accomplish ovarian cancer screening studies.
He images complex ovarian growths with color Doppler, capturing the volume of the mass then rotating it to isolate vascularity as he performs a differential diagnosis of the mass. His primary goal is to diagnose ovarian cancer early, and determine which patients require surgery and which do not.
Crade explains that blood vessels feeding a tumor appear very different from their normal counterparts which grow in an orderly tree-like fashion and taper at the ends. Tumor vessels grow rapidly, their arteries do not have as much musculature in the wall of the vessels and they are larger where musculature is not normal. They demonstrate bizarre branching and some may empty into a vein without capillaries in the intervening space.
Crade uses a technique called “Tissue Block Ultrasound” to analyze an anatomical volume of 3D images and discern the relationship between arteries and veins around the mass.
“Using a feature GE calls MagiCut, I can filet the artery open and see the actual wall becoming smaller then larger then smaller,” says Crade. “I can see inside the lumen of the vessel and look at the complexity of the arteries and veins. We have found that arteries in malignancies have mini-jets of blood flow just distal to areas of narrowing.”
While other clinicians have reported about this rendering of total percentage of vasculature, Crade describes a “beachball sign” when tumors are covered with veins and arteries no matter the direction from which they are viewed.
A correlative benefit of using these imaging techniques is that women who are found to have benign tumors are spared surgery with its possible complications. Crade relates that his study of vascularity using volume ultrasound has significantly improved his diagnostic confidence.
Peter J. Prokell, MD, president of Fort Worth Diagnostic Radiology, P.A., describes their hospital-based radiology group where they have been managing liver transplant patients for about three years. With underlying liver disease caused by a variety of clinical conditions, these patient are often confused and combative because they have hepatic encephalopathy caused by high blood ammonia levels. Additionally, cirrhotic livers are difficult to penetrate with ultrasound, and often these patients are overweight.
This department upgraded their ultrasound imaging system to a Siemens Medical Solutions Sequoia 512 because they found the image quality advantageous for their liver and pancreatic transplant patients.
“The technical difficulty increased with liver transplants because we have to perform a thorough evaluation of the vasculature such as hepatic artery velocities which is not part of a routine abdomen exam,” explains Prokell. Once they had improved the quality of their imaging equipment, the second step was to build additional experience for their technologists. Using techniques such as re-positioning the patient or tilting the patient’s head down may prove beneficial in the pre-operative evaluation phase of treatment.
However, once the surgery has been performed, dealing with the operative site that could include staples, drains and bandages holds additional challenges.
“When patients develop post-operative complications such as hepatic artery stenosis or venous thrombus, they are usually intubated and they’re still,” Prokell describes. “But they have distended abdomens, multiple leads and monitors, and are on a Triadyne bed with an air mattress covering their sides and limiting positioning.”
To image these patients, they often use different transducers, as well as employ color Doppler and power Doppler to determine blood flow.
Prokell describes their technologists as extremely competent and experienced, but he says that can present difficulties for a department as well. It can prove challenging to retain good techs, especially when patients are difficult. Other centers recruit their experienced technologists away to easier jobs.
Larger patients pose unique imaging challenges
The heart of the issue with large patients involves the ability of the sound waves to penetrate to the area of interest to produce the high-quality images required for diagnostic purposes. From a physical perspective, sound wave penetration is challenged by distance and the type of tissue involved. For example, livers are difficult to image because they do not transmit soundwaves well. Couple that fact with a few to several inches of adipose tissue and the problem becomes clear.
A. Thomas Stavros, MD, FACR, director of ultrasound for Invision Radiology Imaging Associates in Englewood, Colo., has been using the Toshiba America Medical Systems Aplio 80 for a number of years. He has been evaluating a substantial upgrade that provides the system with the functionality of the new Aplio XV with Differential Tissue Harmonic Imaging (DTHI). This practice involves evaluation of palpable and/or mammographic breast abnormalities as well as to guide biopsies. Additionally, they do some scans of other areas of the body.
The improvements in imaging resolution for this system are designed to enhance imaging for larger patients who previously were not good candidates for ultrasound imaging.
Stavros explains that the issue with using harmonics in imaging is that the penetration is often reduced. So even though tissue contrast is improved, penetration to an area of interest may be compromised. The Aplio XV is designed as a hybrid system that is capable of creating a combination of harmonics with adequate penetration at various depths while streamlining clinical workflow.
“I can toggle through tissue harmonics, so I can have Tissue Harmonics 1 which is just pure tissue harmonics, or A, B, C or D where I get … a greater percentage of fundamental imaging in the far field with more penetration,” Stavros concludes.
Large patients over 250 pounds at Harbor-UCLA Medical Center in Torrance, Calif., are getting the advantage of HiVision8500 from Hitachi Medical Systems, according to Tom Wright, RDMS, of Harbor-UCLA Medical Center in Torrance, Calif. They use a 3.5 Megahertz (MHz) convex array transducer probe for these patients. “Because we’re using a convex probe, there are more crystals on large transducers and we get better images than a small vector type transducer.”
The system features Tissue Harmonics imaging that uses four levels of penetration to reduce noise. He describes that they can toggle from a very fine-grained image to a coarser image and get more penetration.
“It also adds compound scanning which is an improvement on old techniques of using higher frequencies,” Wright says. “We are filtering or listening for higher frequencies closer to the transducer and then use the lower frequencies at the depth, which increases the clarity and gives a bit more penetration.”
They also make use of HiRes, which they use not so much for the truly heavy patient, but for those in which they are interested in increasing the resolution of the upper portion of the liver, or where there is cirrhosis. HiRes reduces the pixel size so they get higher contrast and better edge enhancement.
Gaziano, who images high-risk mothers, raises the issue of sensitivity towards pregnant women who have weight issues besides those of pregnancy. He explains that they are extremely sensitive towards these women, so that they do not cause embarrassment or shame because there are difficulties in imaging their fetuses. This takes staff who can be caring and reassurance that other factors may enter into the difficulties with imaging, such as those mentioned above.
Brette Sember, author of Your Plus-Size Pregnancy: The Ultimate Guide for the Full-Figured Expectant Mom, says, “The most important thing a clinician can do is realize that many patients are uncomfortable with their bodies and are uncomfortable having medical personnel see their bodies. Adopting an attitude of sensitivity will go a long way in helping patients feel comfortable. Don't assume that because you have seen all types of bodies that patients will know you don't make judgments.”
In interviews with plus-sized women contained in her book, she found there were two common scenarios that upset women. The first was when an external ultrasound was attempted and then the sonographer needed to switch to a vaginal probe. Women were upset when comments were made such as “you have too much fat” or “you’re too fluffy.” The others were when women were asked to hold their pannus (and almost none of the women knew what that term meant) out of the way. She suggests that clinicians be matter of fact and friendly, not avoid looking at the woman’s face and refrain from using the word “fat.”
Finally, she notes, “Women reported that they greatly disliked having the ultrasound done through the navel and found that very painful. They also reported that this made them feel that it was being done because of their size and it might be helpful to explain that sometimes you just can't get a very clear image because of the way the baby is positioned.”
Trends in ultrasound systems include improvements that not only make imaging easier through automatic functionality, but that also provide advanced capabilities to assist clinicians who care for “difficult to image” patients. Transducer design has evolved to provide a wide array of imaging dynamics, and 3D tools have proven invaluable in a number of specific circumstances. While most believe that the obesity epidemic is the primary reason clinicians have problems obtaining clear images of the area of interest, it is only one area of challenge.