Tag Archives: Vascular

Duplex Ultrasound in Arterial Disease in Patients With Critical Limb Ischemia

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Critical limb ischemia (CLI) is the most severe manifestation of peripheral arterial disease (PAD) and presents with severe, chronic rest pain or ischemic skin lesions (ulcer or gangrene). It is the major cause of amputation of ischemic limbs in the United States; the annual incidence of CLI is 500 to 1000 cases per million people. Revascularization by endovascular or open surgical technique is recommended, depending on the severity of the disease.

Many imaging modalities can identify an arterial lesion that is a candidate for endovascular or open surgical technique. Angiography is the gold-standard diagnostic test but it is a high-risk, invasive, and costly procedure (Figure 1).

Figure 1. Aorto-iliac angiography showing acute ischemia involving the right common iliac artery (arrows).

Computed tomography angiography (CTA), using multidetector computed tomography (MDCT) technology and magnetic resonance angiography (MRA), is highly accurate in diagnosing PAD, equivalent to angiography. CT acquisition is rapid and less prone to motion artifacts than MRA is, but its disadvantage is exposure to doses of radiation and the use of iodinated contrast to enhance the vessel visualization. Also, CTA produces streak artifacts from heavy calcification or metallic materials, resulting in a limited evaluation of vascular patency (Figure 2).

Figure 2. CTA image of lower extremities at the onset of acute limb ischemia. The arrow indicates the short-segment occlusion of terminal aorta and bilateral common iliac arteries.

MRA produces an image without contrast or interference from calcium, but its disadvantages are it is time-consuming and expensive, it cannot be performed on patients with metallic devices or on patients who might experience claustrophobia from a closed area, and it might produce false-positive results (Figure 3).

Figure 3. MRA in a patient with pain in the left leg while walking and when resting. The arrowhead indicates stenosis in the distal part of the left common iliac artery.

Duplex ultrasound is widely available for the screening and diagnosis of vascular lesions.  It is safe without risk of radiation exposure, easily repeatable, relatively cost-effective, and causes minimal discomfort. Several studies have shown that duplex ultrasound has good sensitivity, specificity, and diagnostic agreement with angiography in assessment of lower-extremity arterial disease in critical limb ischemia. The peak systolic velocity (PSV) quantified by spectrum analysis from spectral pulsed-wave (PW) Doppler ultrasound was the most common criterion used for diagnosis and categorizing the severity of the disease in most previous studies. The duplex scanning protocol begins with B-mode and color Doppler ultrasound to identify the lesion and assess blood flow before sampling the Doppler signal by spectral PW Doppler ultrasound. The waveform feature analysis (triphasic or monophasic, acceleration time, spectral broadening, turbulence, or direction) and velocity measurement can be obtained at the proximal, distal, and overall points of the lesion when suspicion of abnormality exists. Using mutual interpretation of the findings from B-mode, color, and spectral PW Doppler ultrasound (waveform analysis and velocity measurement) is the key concept of using duplex ultrasound for the diagnosis of vascular disease and PVD (Figure 4).

Figure 4. Duplex ultrasound of the right common femoral artery (CFA). The color Doppler imaging (color box) showed totally occluded CFA in a critical limb ischemia.

Dr. Akram Asbeutah, PhD, DMU-ASUM, ASAR, ASA, FAIUM, SVU, AIR, ASRT, RT(R) ARRT, is a Clinical Associate Professor in the Department of Radiologic Sciences at the Faculty of Allied Health Sciences, Kuwait University/Adjunct, Monash University-Melbourne, Australia.

Ultrasound in Orthopedic Practice

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Point-of-care ultrasound brings great value to patient care in orthopedic practice, especially for soft tissue problems. It offers safe, cost-effective, and real-time evaluation for soft tissue pathologies and helps narrow down the differential diagnosis.Pic1

There are a variety of soft tissue lesions in orthopedic practice with a classic clinical presentation that may not necessitate ultrasound examination for confirmation of diagnosis, for example, ganglion cyst. However, there is value in performing an ultrasound scan for these common soft tissue lesions.

Ganglion cyst on the dorsum of the wrist or radial-volar aspect of the wrist are confirmed based on clinical examination and presentation. Adding ultrasound examination can help differentiate classic ganglion cyst from some rare findings like Lipoma, anomalous muscles, or soft tissue tumors. Ultrasound examination may also be helpful in finding the source of the ganglion cyst or the stalk of the ganglion cyst. This can help pre-surgical planning if resection of the ganglion cyst is desired by the patient and recommended by the surgeon, because arthroscopic or traditional surgical approach may be needed based on the location of the stalk or neck of the cyst.

Images 1 and 2 show examples of two different patients with a similar presentation of slow-growing mass on the digit. Image 1 from patient 1 shows a solid tumor overlying the flexor tendons of the digit, where the mass was palpated. Image 2 from patient 2, shows a cystic mass overlying the tendons of the digit. In both of the cases, masses were painless and slow growing with minimal to no discomfort. Ultrasound is a great tool in differentiating solid vs cystic lesions and can help avoid attempted aspiration of a solid mass when the mass is presented in an area of classic ganglion cyst’s usual presentation.

Another soft tissue problem, where ultrasound is a superior imaging tool is tendon pathology. Ultrasound can help differentiate tendinosis, tenosynovitis, or tendon tears.

In tenosynovitis, tendon by itself shows normal echotexture and uniform appearance but the tenosynovium that surrounds the tendon gets inflamed and appears as hypoechoic halo around the tendon, for example, in image 3, tendons of the first dorsal compartment of the wrist show uniform thickness and fibrillar echotexture, however there is hypoechoic swelling around the tendons, this is an example of tenosynovitis of first dorsal compartment of the wrist.

In tendinosis, tendon loses its fibrillar pattern and appears swollen and may show vascularity on color ultrasound, which is suggestive of neoangiogenesis or angiofibroblastic proliferation. For example, in Image 4, the tendons of the first dorsal compartment of the wrist show focal enlargement, hypoechoic swelling, and loss of normal fibrillar echotexture and tendon appears disorganized with evidence of increased vascularity on color ultrasound. This is an example of tendinopathy or tendinosis.

Focal tendon tears appear as anechoic or hypoechoic focal defects in tendon substance. Image 5 shows a partial tear of the triceps tendon from the olecranon process. The partial tear appears as a focal hypoechoic defect in the tendon, which is confirmed in the long and short axis scan of the tendon.

In full-thickness tears, the tendon is seen retracted proximally with no fiber attachment at the tendon footprint. Image 6 shows an example of a full thickness complete tear of the supraspinatus tendon from its bony attachment at the greater tubercle. The tendon has retracted proximally and the retracted stump is not visible on ultrasound examination.

Image 6

Point-of-care ultrasound adds significant value to clinical examination in an orthopedic setting. It enhances the understanding of a patient’s problem, increases confidence in the care provided, and high patient satisfaction is reported.

In what unexpected ways do you find ultrasound to be useful? Do you have additional tips for using ultrasound in orthopedics?  Comment below or let us know on Twitter: @AIUM_Ultrasound.

Mohini Rawat, DPT, MS, ECS, OCS, RMSK, is program director of Fellowship in Musculoskeletal Ultrasonography at Hands On Diagnostics and owner of Acumen Diagnostics. She is ABPTS Board-Certified in Clinical Electrophysiology; ABPTS Board-Certified in Orthopedics; registered in Musculoskeletal Sonography, APCA; and has an added Point-of-Care MSK Soft Tissue Clinical Certificate.

Determining Umbilical Cord Blood Flow

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Umbilical cord blood flow is among the most highly desired parameters for monitoring fetal well-being. This is because cord blood flow directly reflects placental volume flow, which is considered to be as important in the fetus as cardiac output and lung perfusion are in adults.1 Yet, presently employed noninvasive methods, such as umbilical artery Doppler waveform analyses, use surrogate flow evaluation parameters, such as systolic/diastolic ratios, which do not directly reflect placental-fetal blood flow.2,3 Volume flow estimation overcomes this by measuring true flow, and it has been shown that volume flow changes in the umbilical vein occur before umbilical artery flow indices become abnormal.4

Yet, the present volume flow measurement method has severe problems limiting its utility. These include technical difficulties in flow measurement in umbilical cords and faulty assumptions employed in the measurement. The present method using spectral Doppler is

                 Q = V × A                    (1),

where Q is volume flow, V is the mean velocity through the Doppler sample volume, and A is the cross-sectional area of the vessel of interest. This formula assumes that the 2D flow profile is cylindrically symmetric with a circular cross-section, and the line of the Doppler sampling cuts perfectly through the center of the sampled vessel. The velocity estimates require angle correction, and if the vessel is tortuous, as in umbilical cords, the sampling position placement and angle correction are hard to perform. Multiple investigators have warned that small errors in volume flow components can result in large errors in the calculation of volume flow.5-7

A new, easy-to-perform volume flow method overcomes almost all of the limitations of the standard technique. The new method is angle independent, flow profile independent, and vessel geometry independent. It works as follows:

Volume flow is defined as the total flux across any surface, S, intersecting the vessel. This is written as

Eq2

where Q is again volume flow, V is the local velocity through each area element dA, and “∙” is the dot product which projects the local velocity V onto the normal vector for each area element. This is known as Gauss’s theorem. The intersecting surface, known as the “C” surface, is very simple to obtain using 3D ultrasound (Figure8). In order to validate this method, we obtained an AIUM EER-funded research grant.

Fig

Figure: (A) Four-panel view of a single 3D color flow acquisition of the umbilical cord. The four views are as follows: upper-left is axial-lateral, upper-right is axial-elevational, bottom-left is elevational-lateral (ie, the c-surface), and bottom-right is a rendered 3D reconstruction. Arteries are shown in blue and the vein is shown in red. The schematic in (B) illustrates the orientation of the probe and the corresponding c-surface in the elevational-lateral imaging plane. The vessel colors in (B) match the directionality in (A). The entire umbilical cord passes through the c-surface but only the cross-sections of the umbilical arteries and umbilical vein are illustrated in (B). The two arteries are separated in power Doppler (not shown). (Printed with permission from Pinter et al. J Ultrasound Med. 2012;31(12):1927-34. © 2016 by the American Institute of Ultrasound in Medicine)

We had 2 specific aims: 1) Test the reproducibility of the volume flow measurement, and 2) evaluate the relationship of volume flow to clinical outcome in a high-risk patient population.

In the first aim, we performed studies on 35 subjects between the gestational ages of 22–37 weeks, 26 high risk and 9 normal.9 We attempted to measure umbilical cord blood flow at 3 sites in the cord in each subject, and we averaged 28.3 ± 3.3 (mean ± standard deviation) samples per site. We used a GE LOGIQ E9 ultrasound system with a 2.0–8.0 MHz bandwidth convex array transducer to acquire multiple volume 3D color and power mode data sets. Since we were measuring mean blood flow, we assessed variability using relative standard error (standard error /mean) (RSE). The average RSE for blood flow at each cord position was ±5.6% while the average RSE among the measurements in each subject was ±12.1%.

For the second aim, we compared the volume flow measurements in 5 subjects that developed preeclampsia with the 9 normal subjects. Even with these small numbers, we detected a significant difference between the mean depth-corrected, weight-normalized umbilical vein blood volume flows in the two groups (P = .035). Further, blood flow abnormalities were detected either at the same time or preceded the hypertensive disorder in 4 of the 5 subjects. This is consistent with our prior publication where blood flow changes preceded the onset of pre-eclamptic symptoms in a study subject.8

With the introduction of 2D array transducers, umbilical cord volume flow estimates can be performed in seconds and given the valuable information provided by this method, umbilical cord volume flow will hopefully become a standard component of fetal examinations.

References:

  1. Tchirikov M, Rybadowski C, Huneke B, Schoder V, Schroder HJ. Umbilical vein blood volume flow rate and umbilical artery pulsatility as ‘venous-arterial index’ in the prediction of neonatal compromise. Ultrasound Obstet Gynecol. 2002;20:580-5.
  2. Newnham JP, Patterson LL, James IR, Diepeveen DA, Reid SE. An evaluation of the efficacy of Doppler flow velocity waveform analysis as a screening test in pregnancy. Am J Obstet Gynecol. 1990;162:403-10.
  3. Acharya G, Wilsgaard T, Bernsten GKR, Maltau JM, Kiserud T. Doppler-derived umbilical artery absolute velocities and their relationship to fetoplacental volume blood flow: a longitudinal study. Ultrasound Obstet Gynecol. 2005;25:444-53.
  4. Rigano S, Bozzo M, Ferrazzi E, Bellotti M, Battaglia FC, Galan HL. Early and persistent reduction in umbilical vein blood flow in the growth-restricted fetus: a longitudinal study. Am J Obstet Gynecol. 2001;185:834-8.
  5. Evans DH. On the measurement of the mean velocity of blood flow over the cardiac cycle using Doppler ultrasound. Ultrasound Med Biol. 1985;11(5):735-41.
  6. Gill R. Measurement of blood flow by ultrasound: accuracy and sources of error. Ultrasound Med Biol. 1985;11:625-41.
  7. Lees C, Albaiges G, Deane C, Parra M, Nicolaides KH. Assessment of umbilical arterial and venous flow using color Doppler. Ultrasound Obstet Gynecol. 1999;14:250-5.
  8. Pinter SZ, Rubin JM, Kripfgans OD, Treadwell MC, Romero VC, Richards MS, Zhang M, Hall AL, Fowlkes JB. Three-dimensional sonographic measurement of blood volume flow in the umbilical cord. J Ultrasound Med. 2012;31(12):1927-34.
  9. Pinter SZ, Kripfgans OD, Treadwell MC, Kneitel AW, Fowlkes JB, Rubin JM. Evaluation of umbilical vein blood volume flow in preeclampsia by angle-independent 3D sonography [published online ahead of print December 15, 2017]. J Ultrasound Med. doi:10.1002/jum.14507.

How do you determine umbilical cord blood flow? What problems have you encountered using the traditional method? Comment below or let us know on Twitter: @AIUM_Ultrasound.

Jonathan Rubin, MD, PhD, FAIUM, is Professor Emeritus of Radiology at University of Michigan.