3D TEE for MITRAL VALVE DISORDERS

 

 

 

 

Supra Mitral Valvular Stenosis caused by Left Atrial Myxoma (video)

 

 

EUS for MSK

Review article: Ultrasound elastography for musculoskeletal applications

The British Journal of Radiology, November 2012

 

Xung lực bức xạ âm (ARFI) là một loại strain EUS, trong đó mô bị kích thích từ trong do  xung siêu âm tập trung, thay vì nén bên ngoài (bằng tay hoặc sinh lý). Khi xung siêu âm đi  qua mô, mô mềm di chuyển nhiều hơn so với mô đặc. Sau kích thích và dời chỗ của xung, các tế bào trở về cấu hình ban đầu của nó. Dời chỗ mô do xung đẩy ban đầu có thể đo được bằng cách sử dụng các ứng dụng của một số hồi âm xung thời gian ngắn [short-time pulse echo], cung cấp dữ liệu để so sánh với hình ảnh tham khảo.

Kỹ thuật này cũng có kết quả trong bản đồ đàn hồi mã hoá màu định tính hoặc bản đồ đàn hồi thang xám [greyscale elastogram] miêu tả độ cứng mô tương đối. Phương pháp này có lợi thế tạo hình mô sâu hơn, không thể truy cập khi nén từ ngoài, và đã được sử dụng chủ yếu để tạo hình cho gan, tuyến giáp và vú.

Sóng biến dạng EUS dựa trên một nguyên tắc vật lý hoàn toàn khác. Sóng biến dạng được tạo ra trong mô khi sóng siêu âm quy ước được tạo bởi đầu dò tương tác với các mô. Sóng biến dạng truyền vuông góc với trục dời chỗ do xung siêu âm và giảm nhanh khoảng 10 000 lần hơn siêu âm quy ước. Bằng cách sử dụng thuật toán ultrafast, vận tốc của sóng biến dạng có thể được đo và được sử dụng để đánh giá độ cứng mô bằng cách tính toán mô đun đàn hồi của Young theo công thức:

 

Kỹ thuật này cho kết quả trong cả bản đồ đàn hồi [elastogram] màu mã hóa định tính và  bản đồ đàn hồi định lượng (theo đơn vị  kPa) hoặc vận tốc sóng biến dạng (theo đơn vị cms–1). Phương pháp này khách quan hơn strain EUS, vì không cần nén mô, đánh giá trực tiếp độ  đàn hồi với số đo định lượng. Tuy nhiên, có những mối quan tâm về việc sử dụng của phương pháp này trong các cấu trúc nông, vì sóng biến dạng cần được siêu âm tạo ra ở độ sâu nhất định.

 

EUS thoáng qua, còn được gọi là elastography kiểm soát rung động [vibration-controlled elastography], là một biến thể của sóng biến dạng EUS, theo đó kích thích nén từ ngoài được áp dụng bằng cách sử dụng một short-tone  burst of vibration. Phương pháp này cũng dựa trên ước tính vận tốc của sóng biến dạng trong mô, nhưng để tránh xu hướng gây ra bởi sự phản xạ và nhiễu xảy ra giữa các mô, rung động là tạm thời, do đó sóng chuyển tiếp có thể được tách ra từ sóng phản xạ. EUS thoáng qua chủ yếu được sử dụng trong khám cho bệnh gan.

 

Những viễn cảnh tương lai

 

EUS là đại diện quan trọng nhất cho phát triển kỹ thuật của siêu âm từ sau tạo hình Doppler. Kỹ thuật này có nhiều lợi thế hơn các phương pháp đánh giá đàn hồi khác của mô, chẳng hạn như MR elastography, vì máy có chi phí thấp, nhanh, không xâm hại, và sẵn có tiềm năng lâm sàng rộng hơn. Cho đến nay việc sử dụng EUS có các bằng chứng rất hứa hẹn nhằm đánh giá tính chất cơ học của cơ xương khớp trong lâm sàng.

Dữ liệu sơ bộ cho thấy thậm chí EUS nhạy hơn so với MRI hoặc thiết bị siêu âm thang xám trong việc phát hiện các thay đổi subclinical [tiền lâm sàng] của cơ bắp và dây chằng, và do đó có thể có giá trị cho chẩn đoán sớm và trong y học phục hồi chức năng. EUS có thể được sử dụng như công cụ nghiên cứu sâu vào các cơ chế sinh học và sinh lý bệnh của bệnh cơ gân [musculotendinous].

Tuy nhiên, mặc dù được quan tâm rất lớn trong kỹ thuật, các tài liệu được công bố vẫn còn rất hạn chế và chủ yếu phụ thuộc vào báo cáo ca bệnh hoặc các nghiên cứu không kiểm soát với dân số nghiên cứu nhỏ, và sử dụng kỹ thuật EUS và hệ thống tính điểm khác nhau. Có một số vấn đề kỹ thuật, trong đó thiếu các phương pháp định lượng, xảo ảnh, giới hạn và các biến thể trong  áp dụng các kỹ thuật bởi người dùng khác nhau, làm hạn chế tính lập lại của phương pháp.

Có nghi ngờ về các tiện ích lâm sàng tiềm năng của các công cụ chẩn đoán mới này, như trong hầu hết trường hợp, EUS cho thấy các thay đổi đã rõ trên siêu âm quy ước hoặc Doppler màu, trong khi EUS lại không thay đổi rõ khi bệnh còn ẩn trên tạo hình quy ước, và do đó về lâm sàng là không quan trọng.

Với tất cả những lý do nêu trên, chúng tôi nghĩ rằng nên tổ chức tiếp cận có hệ thống hơn để điều tra các phương pháp mới này. Trước tiên, chúng tôi chủ trương chuẩn hoá [standardisation]  EUS cho các ứng dụng mô mềm, dựa trên đề nghị các nhà sản xuất và sự đồng thuận giữa người sử dụng, bằng cách sử dụng các tham số chẳng hạn như kích thước của elastogram, sử dụng gel/adaptor/pad, các hệ thống tính điểm và v.v.. Điều này hết sức quan trọng trong việc đạt được sự nhất quán trong việc áp dụng các kỹ thuật và sẽ cho phép so sánh giữa các nghiên cứu. Để khắc phục các vấn đề kỹ thuật liên quan đến việc sử dụng EUS trong mô ở nông,  các hợp tác chặt chẽ giữa ngành công nghiệp và các nhà nghiên cứu lâm sàng sẽ cho phép những kinh nghiệm lâm sàng được sử dụng cho sự phát triển của giao thức tối ưu hóa dành riêng cho ứng dụng trong cơ xương khớp.

Thứ hai, chúng ta cần phải cẩn thận thiết lập các chỉ định cho EUS. Các mục tiêu lý tưởng trên nghiên cứu đoàn hệ [cohort] của bệnh nhân có triệu chứng nhưng non-ultrasound-evident, bệnh nhân có nguy cơ hoặc bệnh nhân ở giai đoạn rất sớm của bệnh, để điều tra cho dù EUS nhạy hơn so với tạo hình ảnh quy ước trong mô tả thay đổi lâm sàng quan trọng sớm hơn. Nghiên cứu đa trung tâm có kiểm soát lâu dài  [multicentre long-term controlled studies] là cần thiết;  các nghiên cứu này nên bao gồm các quần thể lớn của lứa tuổi khác nhau và mức độ hoạt động với theo dõi lâu dài và mối tương quan với mô học, tạo hình quy ước (siêu âm và MRI) và dữ liệu cơ sinh học và lâm sàng, để mô tả các mô hình và tính chất của các dấu hiệu EUS và ý nghĩa lâm sàng của chúng.

Cuối cùng, các thuật toán mới cho phép đánh giá định lượng tính đàn hồi như EUS sóng biến dạng hoặc ARFI nên được nghiên cứu và so sánh với strain EUS định tính.

 

Kết luận

Do thiếu tiêu chuẩn hóa và nghiên cứu  có giới hạn,  EUS trong hình thức hiện tại  vẫn còn là một kỹ thuật rất chủ quan, với giá trị lâm sàng gây tranh cãi. Với tiêu chuẩn hóa và cấu trúc thêm nghiên cứu, EUS có thể trở thành một công cụ bổ sung có giá trị trong việc điều tra của bệnh cơ xương khớp.

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Acoustic radiation force impulse (ARFI) is a type of strain EUS whereby tissue is excited internally by a focused ultrasound pulse, instead of external (manual or physiological) compression [14, 35–37]. As the ultrasound pulse travels through the tissue, soft tissue experiences larger displacement than hard tissue. After the excitation and displacement by the pulse, the tissue relaxes to its original configuration. The tissue displacement by the original push pulse can be measured using the application of several short-time pulse echoes, which provides data for comparison with the reference image [14, 35–37].

The technique also results in a qualitative colour-coded or greyscale elastogram depicting relative tissue stiffness. This method has the advantage of imaging deeper tissue, not accessible by superficial external compression, and has been used mainly for liver, thyroid and breast imaging [14, 35–37].

Shear wave EUS is based on a completely different physical principle. Shear waves are generated within tissue when the conventional ultrasound waves produced by the transducer interact with tissue [38]. Shear waves propagate perpendicular to the axial displacement caused by the ultrasound pulse and attenuate approximately 10 000 times more rapidly than conventional ultrasound [38]. By use of ultrafast algorithms, the velocity of shear waves can be measured and used to evaluate tissue stiffness by calculating the elastic Young’s modulus according to the formula: 

This technique results in both qualitative colour coded elastograms and also quantitative maps either of elasticity (in kPa) or of shear wave velocity (in cms–1). This method is more objective than strain EUS, because of the lack of tissue compression, the direct assessment of elasticity and the quantitative measurements provided. However, there are concerns about the use of this method in very superficial structures, as a certain depth of ultrasound penetration is needed for shear waves to be produced [14, 38].

Transient EUS, also known as vibration-controlled elastography, is a variant of shear wave EUS, whereby

the external compression is applied by using a short-tone burst of vibration [39]. The method also relies on the estimation of the velocity of shear waves in tissue, but in order to avoid the bias caused by reflections and

interferences occurring between the tissues, vibration is transient, so that forward waves can be separated from the reflected waves [39]. Transient EUS is mainly used in examinations for liver disease [14, 39].

Ultrasound elastography for the examination of tendons

The Achilles tendon has provided most of the clinical data available so far in musculoskeletal applications; it was the first area to be investigated using free-hand strain EUS (Table 1). In a study of 50 asymptomatic and

sonographically normal Achilles tendons in healthy volunteers, the normal tendons were found to have two distinct EUS patterns (Figure 1) [17]. They were either homogeneously hard structures or, in the majority of cases (62%), they were found to have considerable inhomogeneity with soft areas (longitudinal bands or spots), which did not correspond to any changes in B-mode or Doppler ultrasound [17].

These findings were confirmed in two studies by the same research group, comparing normal (asymptomatic) and abnormal (symptomatic) tendons [18–20]. The asymptomatic tendons were found to be homogeneously

hard in 86–93% of cases, containing mild softening (yellow) in 7–12% of cases and containing marked softening (red) in 0–1.3% of cases [18–20]. By contrast, symptomatic tendons were found in EUS to contain marked softening in 57%, mild softening in 11% and nosoft areas (hard structures) in 32% of cases [18]. The alterations in asymptomatic tendons were mainly observed in the tendon mid-portion and were not always found to correspond to alterations in conventional ultrasound [18–20]. Mild softening (yellow) was not correlated with conventional ultrasound abnormalities, whereas marked softening (red) was found mainly in cases with ultrasound disease, so the authors suggest that only marked soft areas should be considered as abnormal in Achilles tendon EUS [19, 20] (Figure 2). The nature of the EUS alterations found in asymptomatic and sonographically normal tendons is not yet completely understood; it is suggested that they may either correspond to early (pre-clinical) changes not yet evident using ultrasound or to false-positive findings, secondary to tissue shifting/non-axial movement at interfaces between collagen fibres [17–20]. To date no histopathology or follow-up studies are available to elucidate the above presumptions.

However, another study used strain EUS to assess 12 patients with Achilles tendinopathy using ultrasound and MRI and found increased stiffness in the abnormal tendons, compared with the non-symptomatic, which were softer [21]. These findings are completely different from those previously reported and emphasise the need for further research on EUS of the Achilles tendon.

Technical considerations and limitations of ultrasound elastography

The major problem in the application of EUS is that there are a wide variety of techniques and processing algorithms currently available for producing and displaying elastographic images and therefore the findings as well as the artefacts or limitations may be highly dependent on the technique and may be specific to a specific system. Experience regarding technical problems and the means of resolving them has resulted from the use of free-hand compression EUS. Compression EUS is technically very challenging in terms of the proper application of the technique. It is difficult to produce high quality, artefact-free cine loops of decompression–

compression cycles. The problems are associated with either inherent limitations of the technique itself or the characteristics of the musculoskeletal system.

A major issue associated with compression EUS is determining the correct amount of pressure to be applied on tissue. The pressure should be moderate, described as the level of pressure that maintains contact with skin and for which the association between pressure and strain is proportional [6]. Very high or low pressure should be avoided, as the elastic properties of tissue become non-linear [6]. Most EUS systems now provide software, which allows a feedback of the amount of pressure as a visual indicator/bar displayed on the screen alongside sonographic images thus ensuring the correct application of pressure. To minimise intra-observer variation and avoid transient temporal fluctuations, the scoring or measurements in the elastograms should be based on examination of entire cine loops instead of single static images [17, 20, 34]. The most common method to assess the elastograms is by viewing representative images derived from cine loops of at least three compression–relaxation cycles [17–20, 34]. The images should be chosen at the compression phase and in the middle of each cycle, as the calculation of the elastogram at the initial and final stages of each cycle will be inaccurate [18–20].

Another major problem in strain EUS is the lack of quantitative measurements. This has led researchers to use various methods for the assessment of the elastograms, which include semi-quantitative measurements (strain ratio) [17], qualitative assessment visual assessment of elastograms using patterns, scores or grades [17–20], or by using commercially available external computer software [25, 26]. This has led to considerable confusion in the interpretation of the findings, a lack of reproducibility and difficulty in comparing the results from different studies, even if the same technique (strain EUS) is applied in all cases.

When using EUS for examining musculoskeletal tissue, special issues should be taken into consideration.

In conventional musculoskeletal ultrasound the amount of pressure should be as light as possible, so as not to distort the underlying tissues (e.g. fluid within bursa or synovial cavity), whereas in EUS a certain amount of

pressure is necessary to allow the correct application of the technique. The examination probe should always be held perpendicular to the tissue to avoid anisotropy, as the B-mode appearance influences the acquisition of EUS data [18–20]. Although tendon images should be taken in both transverse and longitudinal planes, longitudinal images are of better quality, as it has been shown that the reproducibility of transverse images of the Achilles tendon is less than that of longitudinal images because of artefacts at the medial and lateral sides of the image secondary to unilateral pressure and out-of-plane movements of the transducer [17]. There are elasticity changes at the borders of the elastogram attributed to inhomogeneous application of pressure [17–20], and so overlapping images should be acquired to overcome this problem. There are also limitations and difficulties related to the anatomy of the area examined. EUS is especially problematic in cases of superficial protuberant masses and in areas with prominent adjacent bony structures (e.g. at the level of the malleoli when examining tibialis posterior and the peroneal tendons), where it is difficult to apply uniform compression over the entire region of interest [34].

Another important parameter is the size of the elastogram. The elastogram displays the elasticity of each tissue relative to the remaining tissue within it. Therefore, the amount and level of stiffness of the surrounding tissue influences the appearance of the tissue of interest. This is not a major problem in tissues such as the breast where the surrounding tissue is fairly homogeneous (fat and glandular tissue). In musculoskeletal EUS, however, the elastogram may include tissues with wide elasticity differences (fat, tendon, bone, muscle), leading to a wider scatter in the acquired elasticity data. For the Achilles tendon, the suggested standard size for longitudinal scans is a depth of three times the tendon and about three-quarters of the screen, and for transverse scans the paratenon should be included [20]. However, this suggestion is not universally applied, leading to difficulties in comparisons between studies.

Another standardisation problem is the distance between the probe and the tissue of interest. In many musculoskeletal applications, the tissue of interest is very superficial or even lies directly under the skin (e.g. Achilles tendon). In most ultrasound systems a minimum distance (usually 1.2 mm) from the skin is needed to place the box of the elastogram, so in thin people the use of gel pads or probe adaptors is necessary to increase the distance between the skin and probe [18–21]. Using these stand-off devices has been proven not to influence the appearance of the elastogram [18, 19]. In conventional musculoskeletal imaging, the use of large amounts of gel is common practice in order to create an even surface and to reduce the amount of pressure on the tissue. However, when performing EUS for musculoskeletal applications, care should be taken not to include the gel in the box of the elastogram, as it results in dramatic changes, making the tendons appear considerably stiffer compared with the gel (Figure 5).

Several artefacts can be encountered during the application of EUS in musculoskeletal tissues, which reduce the quality of the elastograms and may lead to misinterpretation of the images. These include fluctuant

changes at the edges of the elastogram and at the medial and lateral borders of thin structures (such as theAchilles tendon in the axial plane) due to instability and out-of-plane movement of the transducer (Figure 1b) [17–19]. Occasionally red (soft) lines may appear around calcifications or phleboliths, behind dense bone and at the superficial margin of homogeneous lesions (such as lipomata; Figure 2b) [20, 34]. Similar changes (red lines) appear at the interfaces between tissues (such as between adjacent muscles), due to tissue shifting (Figure 4b).

Characteristic artefacts are also associated with cystic masses, which appear as a mosaic of all levels of stiffness (all colours), and with lesions adjacent to major vessels, where pulsations result in mistracking of echoes [34].

Familiarity with the above artefacts is important, as they should be excluded from the qualitative or quantitative scoring of the elastograms.

Future perspectives

EUS probably represents the most important technical development in the field of ultrasonography since Doppler imaging. It has many advantages over other methods of tissue elasticity estimation, such as MR elastography, as it is a low-cost, fast, non-invasive system, and has the potential of wider clinical availability. The evidence so far seems very promising that EUS can be used to assess the mechanical properties of musculoskeletal tissues in the clinical setting.

Preliminary data show that EUS may even be more sensitive than MRI or grey-scale ultrasound in detecting subclinical changes of muscle and  tendon, and therefore could be valuable for early diagnosis and during

rehabilitation medicine. EUS could be used as a research tool to provide insight into the biomechanics and pathophysiology of musculotendinous disease.

However, despite the great interest in the technique, the published literature is still very limited and mainly depends on case reports or non-controlled studies with small study populations using various EUS techniques and scoring systems. There are several technical issues, including a lack of quantification methods, artefacts, limitations and variation in the application of the technique by different users, which limit the reproducibility of the method.

There are doubts regarding the potential clinical utility of this new diagnostic tool, as in most cases the EUS showed changes already evident on conventional ultrasound or colour Doppler imaging, whereas EUS changes not evident on conventional imaging were occult, and therefore not clinically important.

For all of the above reasons, we think that a more systematic and structured approach to the investigation of this new method should be undertaken. First, we advocate standardisation of EUS for soft tissue applications, based on the manufacturers’ suggestions and consensus between users, employing parameters such as the size of the elastogram, the use of adaptors/pads/gel, the scoring systems and so on. This will be of paramount importance in achieving consistency in the application of the technique and should allow comparisons between studies. In order to overcome the technical issues associated with the use of EUS in superficial tissues, close collaboration between the industry and clinical researchers will allow the clinical experience to be used for the development of optimised protocols dedicated to musculoskeletal applications.

Second, we need to carefully establish the indications for EUS. These would ideally focus on the cohort of patients with symptomatic but non-ltrasound-evident disease, patients at risk or patients at very early stages of disease, in order to investigate whether EUS is more sensitive than conventional imaging in depicting earlier clinically important changes. Multicentre long-term controlled studies are needed; these should include large populations of different ages and levels of activity with long-term follow-up and correlation with histology, conventional imaging (ultrasound and MRI), and biomechanical and clinical data, in order to describe the pattern and nature of EUS findings and their clinical significance.

Finally, newer algorithms that allow quantitative assessment of elasticity such as shear wave EUS or ARFI should be studied and compared with qualitative strain EUS.

Figure 5. The impact of gel on the strain elastograms. (a, b) Longitudinal and (c, d) axial elastograms of the same asymptomatic

Achilles tendon (T). The inclusion of a small amount of gel in the elastogram (b, d) results in a homogeneously stiffer tendon without areas of distinct softening (red), which are evident when no gel is included (a, c). The level of pressure and the ultrasound elastography settings were kept stable.

Conclusion

Owing to lack of standardisation and limited research, EUS in its current form remains a highly subjective technique, with debatable clinical value. With the proper standardisation and further structured research, EUS may become a valuable supplementary tool in the investigation of musculoskeletal disease.

Figure 3. Longitudinal shear wave elastograms of a normal (a) Achilles and (c) patella tendon, as well as (b, d) a case of distal patella tendinopathy in a 23-year-old football player. The elasticity qualitative and quantitative scale is presented at the upper right corner of the images. Measurements (mean, minimum, maximum and standard deviation) within the circular region of interest (ROI) are presented in kilopascals ranging from 0 (dark blue) to 300 (dark red). (a, c) The normal Achilles and patella tendons (T) appear as homogeneous stiff (red) structures, as opposed to fat, which is homogeneously soft (blue). (a) The mean stiffness of a representative area at the mid-portion of the Achilles free tendon is 300 kPa. (d) In the case of distal patella tendinopathy, the tendinopathic area appears hypoechoic with neovascularity (asterisk). (b) In the corresponding elastogram, the abnormal area appears softer (blue; mean elasticity 40.94 kPa) compared with the stiffer normal tendon (red; mean elasticity 261.16 kPa). The small amount of fluid in the deep infrapatella bursa appears softer than the tendinopathic area (blue, mean elasticity 34.38 kPa).

THIẾU MÁU NÃO SƠ SINH : SIÊU ÂM DOPPLER NÃO và BỤNG

Abstract

OBJECTIVE. The purpose of this article is to describe the role of cerebral and abdominal sonography with color Doppler sonography, including assessment of multiorgan tissue perfusion, in neonates with hypoxic-ischemic injury.

CONCLUSION. Bedside sonography and color Doppler sonography of the brain and abdominal organs can provide reliable and comprehensive information in asphyxiated neonates with hypoxic-ischemic injury. This article, which includes pathologic correlation, illustrates the major sonographic findings in this critical population.

Perinatal asphyxia is a major contributor to neonatal death and morbidity. Each year, approximately 23% of the 4 million neonatal deaths and 8% of all deaths at younger than 5 years of age throughout the world are associated with signs of asphyxia [1]. Indeed, even at referral centers in developed countries, death or moderate to severe disability occurs in 53–61% of infants diagnosed as having moderate to severe hypoxic-ischemic encephalopathy [2]. Several randomized controlled trials have shown that therapeutic hypothermia is a neuroprotective strategy that improves death and disability in neonates with moderate to severe hypoxic-ischemic encephalopathy, and this treatment has been adopted as the standard of care by most centers around the world [2].

During asphyxia, gas exchange between the fetus and the placenta is compromised, resulting in fetal hypoxia, hypercarbia, and acidosis. Subsequently, a marked redistribution of blood flow occurs, with an increase in the flow to the brain, heart, and adrenal glands and a decrease in the blood flow to the kidneys, bowel, and skin. Indeed, multiple-organ failure has been reported in 50–60% of neonates with severe perinatal asphyxia [3]. If this process lasts long enough, cerebral blood flow decreases by a combination of abnormal cerebral autoregulation and systemic hypotension, leading to cerebral hypoperfusion and subsequent hypoxicischemic injury [4]. During the postasphyxiated period, an increase in cerebral blood flow may unfold, with the onset generally within the first few hours of life and duration of many hours or days. This chain of events is called reperfusion or the hyperemic phase and is responsible for secondary brain injury.

In neonates with hypoxic-ischemic encephalopathy, high levels of cerebral blood flow measured at 12–24 hours of life have been associated with more severe brain injury [3]. A substantial proportion of asphyxiated infants (35–85%) exhibit predominantly cerebral deep nuclear neuronal involvement [5], and injury to these areas has been associated with unfavorable neurologic outcome [5, 6]. Therefore, measurements of brain perfusion with dynamic color Doppler sonography during this period may provide information that correlates with reperfusion injury.

Dynamic Color Doppler Sonography for Tissue Perfusion Measurements

Over the past few years, we have used a recently developed software program (Pixelflux, Chameleon-Software) to dynamically quantify the color Doppler signals and obtain tissue perfusion measurements, specifically of the brain and bowel [7]. This color Doppler quantification method provides dynamic blood flow data (during the cardiac cycle) and perfusion velocity in a chosen region of interest (ROI) from a standard color Doppler video, without IV contrast administration. Tissue perfusion is quantified, taking into consideration the amount of blood flow through a specific tissue during a complete cardiac cycle and therefore reflecting the differences between systolic and diastolic perfusion in the small vessels of the specified area. The average values of the flow velocity and area inside the ROI are measured during the cycle and used for the calculation of tissue perfusion intensity (PI):

where v is the mean velocity of pixels, A is the area of all color pixels and A _ROI is the area of the ROI.

All this calculation is done automatically for images encompassing one full heart cycle, which is also detected automatically by the software [7].

For all studies, the color Doppler parameters are standardized and kept constant for comparison between studies (color gain, 40; scale, 7.5 cm/s). Color Doppler videos with major motion artifacts are excluded, and the ROI is only determined in areas without artifacts through-out the duration of the video. All neonates who have congenital heart disease or are hemodynamically unstable are excluded. During these studies, it is critical to obtain information on several physiologic parameters, such as oxygenation (SpO₂ or Pao₂), carbon dioxide levels (Pco₂ or TcPco₂), blood pressure (systolic, mean, and diastolic), and body temperature (skin and esophageal). Information on the use of medications, such as inotropes, vasoconstrictors, vasodilators, and sedatives, is also important because it can affect tissue perfusion. Clinical or electroencephalography seizures should also be recorded.

In asphyxiated neonates, brain monitoring and assessment are usually done by electroencephalography and MRI [5, 8]. However, ultrasound is an attractive tool given its portability and lack of ionizing radiation. In this article, we will illustrate the most common findings of sonography performed at the bedside to assess the brain and abdominal organs in asphyxiated neonates. We will also describe our experience with the use of dynamic color Doppler sonography. Although the clinical usefulness of the information obtained with dynamic color Doppler sonography has not yet been established in this population, such tissue perfusion measurements have been applied in many different settings with positive and encouraging results. Indeed, tissue perfusion measurements using dynamic color Doppler sonography have been proven useful to describe local inflammatory activity in bowel segments affected by Crohn disease in pediatric patients [9], assess perfusion of transplanted kidneys [10], and differentiate stages on metastatic lymph nodes [11].

Brain

As indicated previously, MRI is the standard imaging modality of the brain in neonates with perinatal asphyxia because it provides anatomic and functional information that help determine the severity of the disease and the prognosis. It depicts different patterns of injury, such as watershed injury or involvement of basal ganglia and thalami, as seen in the more severe cases. Although head sonography is thought to be less accurate than MRI, in a recent study, a good correlation between studies and MRI of the brain parenchyma was shown in the assessment of hypoxic-ischemic injury [8]. This suggests that head sonography may be a more effective modality than previously described. Moreover, head sonography remains an excellent screening tool for use in neonates too critically ill to be transported to the MRI suite.

In our institution, head sonography is performed in neonates with hypoxic-ischemic encephalopathy, using a 9S4-MHz sector transducer. The most common head sonography findings in neonates with hypoxic-ischemic injury are brain swelling with echogenic subcortical white matter (Fig. 1A), increased cerebral echogenicity with or without loss of gray-white matter differentiation, and basal ganglia involvement (Fig. 2A). Intraventricular bleed (Figs. 3A, 3B, and 3C), although uncommon, has also been described in term neonates with hypoxic-ischemic injury. Head sonography can also assess pulsed Doppler flow velocities and the resistive index of the cerebral arteries [3].

During the head sonography examination, we also perform dynamic color Doppler sonography (color gain, 40; scale, 7.5 cm/s) with an 11LW4-MHz linear transducer. DICOM color Doppler videos of the basal ganglia blood flow are obtained and recorded in the coronal plane (Figs. S1B and S2B, supplemental videos, can be viewed from the information box in the upper right corner of this article). These videos are later analyzed using dedicated software [7] to quantify the cerebral perfusion intensity of the area (Figs. 1A, 1B, 1C, 1D, 2A, 2B, 2C, 2D, 2E, and 2F). Data obtained with this technique are currently under investigation, with encouraging results, as a potential marker of reperfusion injury (Faingold R et al, presented at the 2011 annual meeting of the International Paediatric Radiology Congress).

 

Bowel

Perinatal asphyxia may also have devastating consequences to the gastrointestinal tract, and gastrointestinal dysfunction has been described in 29% of neonates with perinatal asphyxia [12]. Sonographic evaluation of the intestinal tract can provide information on intestinal appearance, blood flow velocities, and mural perfusion. At our institution, gray-scale abdominal sonographic images of the bowel are acquired with linear transducers ranging from 11 to 18 MHz. The spectrum of sonographic findings varies with the severity of disease and includes normal bowel wall echotexture, bowel wall edema, and presence of sloughed mucosa. Sloughed mucosa is defined as the presence of a halo or echogenic material with echotexture similar to the mucosa within the intestinal lumen (Figs. 4A, 4B, 4C, and 4D).

In severe hypoxic-ischemic injury, a significant decrease in mean blood flow velocities and increase in the resistive index were reported in the superior mesenteric artery using pulse Doppler evaluation [3]. However, end-organ involvement has not been described. Tissue perfusion is a crucial prerequisite for normal function; therefore, quantification of bowel perfusion is important in the assessment of these critical patients. Indeed, intestinal mural perfusion patterns have been described before in patients with Crohn disease [9] and neonates with necrotizing enterocolitis [13] using color Doppler sonography and dynamic color Doppler sonography. Intestinal perfusion findings of these studies were classified as preserved intramural perfusion, bowel hyperemia, or decreased bowel perfusion (Figs. 5A, 5B, 5C, 5D, and 5E). During abdominal sonography, we have also obtained DICOM color Doppler videos of the mural blood flow (Figs. S5A and S5D, supplemental videos, can be viewed from the information box in the upper right corner of this article) using an 11LW4-MHz linear transducer (color gain, 40; scale, 7.5 cm/s) to assess intestinal perfusion intensity (Cassia G et al, presented at the 2011 annual meeting of the International Paediatric Radiology Congress). These data are also currently under investigation to evaluate whether accurate assessments of bowel perfusion in asphyxiated infants can help in staging the disease and understanding the mechanisms of intestinal autoregulation.

Kidneys

Perinatal asphyxia is one of the most common causes of acute kidney injury in neonates. The prevalence range has been reported between 30% and 56%, probably an underestimation given the limitations in the diagnostic criteria [14]. Acute kidney injury may develop with or without oliguria or increase in serum creatinine levels. Imaging is not routinely used; however, gray-scale sonography may show parenchymal hyperechogenicity and loss of corticomedullary differentiation. Decreased blood flow velocity in the renal artery with pulse Doppler imaging has been described in severe hypoxic-ischemic injury [3] (Figs. 6A, 6B, 6C, 7A, and 7B).

Adrenal Glands

Adrenal swelling and thickening have been described in neonates with asphyxia and other causes of perinatal stress [15]. Sonographically, they may be enlarged or may loose their central echogenic stripe (Fig. 8A). Congestion and depletion of cortical lipids are the typical histologic changes of perinatal asphyxia.

Adrenal hemorrhage is relatively uncommon in neonates (Figs. 8B and 8C) but has been described in association with asphyxia, birth trauma, septicemia, and bleeding diathesis. The incidence ranges from approximately 1.7 per 1000 of autopsied neonates to approximately 3% in abdominal ultrasound studies [16].

Liver

Perinatal asphyxia is known to be a possible cause hepatic injury. However, the real incidence of liver injury is not well established because studies have used different definitions on the basis of abnormalities of liver enzymes or autopsy findings. Histologic changes in the liver are seen only with the most severe degrees of asphyxia. One study reported hepatic injury in up to 39% of neonates with asphyxia [17]. Imaging of the liver does not play an important role in the evaluation of these neonates. The liver is usually homogenous or may show geographic hyperechogenic areas (Figs. 9A and 9B).

Conclusion

Sonography of the brain and abdominal organs can provide reliable and comprehensive information in asphyxiated neonates with hypoxic-ischemic injury. Dynamic color Doppler sonography is a simple bedside technique and a promising tool to be used in the assessment of multiorgan perfusion injury, monitoring the response to several drugs or interventions, and helping with the prediction of long-term outcomes in asphyxiated neonates. It also may provide the necessary information to improve the understanding of the changes in cerebral and visceral perfusion occurring in these infants over time.

 

NHÂN CA U BÀNG QUANG XUẤT HUYẾT @ MEDIC

History
An 18-year-old man with an established history of neurofibromatosis type 1 (NF1) presented with weight loss and umbilical protrusion. He denied any pain, urinary symptoms, or gastrointestinal symptoms. An initial ultrasound (US) examination of the abdomen and pelvis demonstrated bilateral hydronephrosis and bladder wall thickening, which led to urologic consultation and, ultimately, cystoscopy. At cystoscopy, the bladder mucosa was noted to be irregular and compressed, but no focal intraluminal mass was appreciated. There was some apparent difficulty in identifying the ureteral orifices.
Further imaging with computed tomography (CT) and magnetic resonance (MR) imaging showed a large mass involving the bladder wall and causing the hydronephrosis. Bilateral nephrostomy tubes and ureteric stents were placed in an antegrade fashion, which succeeded in relieving the urinary obstruction.

 

 

Subsequently, the nephrostomy tubes were removed and the ureteric stents were left in place. The patient underwent a surgical biopsy, which demonstrated pathologic changes diagnostic of neurofibroma. The possibility of malignant degeneration was considered given the size of the mass, resulting in the referral of the patient to a tertiary-care center for radical cystectomy and urinary diversion.

 

Myofibroblastic tumor, also known as inflammatory pseudotumor or pseudosarcoma, is a benign tumor with mesenchymal origin. Bladder location is very uncommon. We report the case of a 58-year-old man with a history of von Recklinghausen’s disease who complained for painless macroscopic hematuria 5 months after suprapubic prostatectomy. The radiograph evaluation revealed a bladder tumor, and the pathologic examination following a transurethral resection showed inflammatory myofibroblastic tumor of the bladder. The patient finally underwent a radical cystectomy due to the uncertain pathogenesis of inflammatory myofibroblastic tumor as well as the rarity of cases published on bladder tumors in Von Recklinghausen’s patients.