TẠO
HÌNH SWE CÁC HẠT GIÁP
V.
CANTISANI et al
Hầu
hết các máy siêu âm đàn hồi đo tốc độ sóng biến dạng bằng ROI nhỏ có kích thước
chọn trước cố định đặt trong vùng muốn khảo sát. Kỹ thuật này được gọi là điểm siêu âm đàn hồi p-SWE [SW elastography
point] và cung cấp kết quả số của SWS của mô trong ROI box cả bằng đơn vị m/s hoặc
kPa. Giá trị độ cứng cao tương ứng với tốc độ cao. Kỹ thuật ARFI là nhãn hiệu phần mềm đầu tiên dùng p-SWE.
Mặt
khác, vài máy có khả năng hiển thị số đo ARFI mã hóa màu trong môt hộp ROI lớn,
là bản đồ tốc độ, còn gọi là hình đàn hồi hay elastogram. Kích thước
của elastogram do người đo kiểm soát bằng tay và hiển thị chồng lên hình
B-mode, gọi là 2D-SWE.
Trên
hình siêu âm đàn hồi có những vùng không màu có thể do chứa dịch, vôi hóa,
hoặc không thể đo do vấn đề kỹ thuật.
Trên vài máy có hiển thị số đo là “X.XX” hoặc “0.00” vì hạt giáp chứa dịch hay
vôi hóa.
Với
p-SWE, đôi khi máy không đo chính xác do một số yếu tố vì chuyển động hoặc
nhiễu, hoặc biên độ quá thấp để tạo sóng biến dạng, hay hạt giáp quá cứng nên
tốc độ biến dạng quá cao không thể lấy mẩu. Chẳng hạn như ARFI khi không thể đo
sẽ hiển thị “X.XXm/s”, khi đó chỉ cần đổi vị trí đầu dò và đo lại.
GIÁ TRỊ CHẨN ĐOÁN SWE CÁC HẠT GIÁP:
Theo y văn , đối với p-SWE tốc độ sóng biến dạng của tuyến giáp
bình thường là 1, 60 ± 0,18 m/s. Với 2D-SWE dùng SSI là 2,6 ± 1,8 m/s và 20,8 ±
10,4 kPa . Phân biệt hạt giáp lành với ác tính, SWE có giá trị ngưỡng từ 3,65
m/s to 4,70 m/s (34, 5–66 kPa).
Tốc độ sóng biến dạng
của tổn thương ác tính cao hơn lành tính có ý nghĩa, với giá trị cao hơn
2,87m/s gợi ý ác tính. Tất cả nghiên cứu và phân tích hồi cứu cho rằng SWE
(p-SWE và 2D-SWE) có thể là phương tiện bổ sung có ích giúp phân biệt hạt giáp lành
tính và ác tính.
Dịch từ Atlas of Elastosonography, D-A CLEVER et al, © Springer Intern Publ. Switzerland 2017.
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11. Always bear in mind that, as with strain elastography, malignancy may appear genuinely soft, albeit rarely. Follicular carcinomas, in particular, can be soft and difficult to distinguish from benign nodules.
12. For good documentation, some authors recommend, for every nodule, the acquisition of three cine loops, each of at least 10 s of duration.
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How to Improve the Examination
1. In all SWE techniques, for accurate measurements, a slight contact of the probe to the skin is essential, as pressure applied by the probe alters the measurements and causes artifacts of increased stiffness. For this reason experience is required to perform reliable examinations and SWE quantification. Liberal use of ultrasound coupling gel can help maintain only slight contact with the skin. The patient should perform adequate breath hold.
2. If you encounter a pattern of red in the near field, also called a vertical artifact, you may reduce it by minimizing probe compression.
3. The isthmic nodules, compressed against the trachea, are the most at risk to effect of probe pressure. To avoid the artifactually increased measured stiffness, some authors advise the use of paracoronal scanning in order to avoid compressing the nodules against the trachea.
4. The ROI should include as much as possible of the area of the nodule. Normal thyroid parenchyma should not be included in the ROI.
5. ROI must be placed in the nodule avoiding cystic or calcified areas as these alter the measurements. However, the use of the standard size ROI in p-SWE sometimes makes it impossible to exclude fluid and calcified areas of a nodule.
6. Choosing a correct preset is important to acquire accurate measurements, and the preset should be 0–180 kPa for the thyroid application. Increase the elasticity color gain to its maximum till the noise starts to appear in the elasticity image, because this will aid in acquiring good color sensitivity elastograms.
7. With 2D-SWE in order to obtain the most significant quantitative readouts, ROIs should be placed on the stiffest part of a lesion as shown in the velocity map (2D-SWE elastogram). Malignancy is often very heterogeneous in stiffness; it is useful to choose the stiffest site for the measurement.
8. In the elasticity image, there can be areas with no color that may be due to fluid content, calcification, or impossible velocities’measurements due to technical problems. In some systems the displayed measurements show “X.XX” or “0.00” because these nodules contain cysts and calcifications. Cysts, when containing nonviscous fluids, do not support shear waves, and so they appear as color voids, usually seen as black regions where the anechoic B-mode layer shows through. On the other hand, when the cyst fluid is viscous, shear wave signals may be seen and would display a soft region.
9. With p-SWE, sometimes the system cannot calculate an accurate measurement due to a variety of factors such as motion or noise or probably a too low amplitude of the generated shear wave or even too high stiffness in the nodule with a too high shear wave speed that cannot be sampled. ARFI for example, when it cannot yield a measurement, displays “X.XX m/s” instead of the expected numeric value. In such an occurrence,slightly change the position of the probe and repeat the evaluation.
10. With ARFI, in the
experience of some researchers, ten measurements were needed to obtain an
average which yielded a reliable accuracy. Another research
group had good results with five measurements.1. In all SWE techniques, for accurate measurements, a slight contact of the probe to the skin is essential, as pressure applied by the probe alters the measurements and causes artifacts of increased stiffness. For this reason experience is required to perform reliable examinations and SWE quantification. Liberal use of ultrasound coupling gel can help maintain only slight contact with the skin. The patient should perform adequate breath hold.
2. If you encounter a pattern of red in the near field, also called a vertical artifact, you may reduce it by minimizing probe compression.
3. The isthmic nodules, compressed against the trachea, are the most at risk to effect of probe pressure. To avoid the artifactually increased measured stiffness, some authors advise the use of paracoronal scanning in order to avoid compressing the nodules against the trachea.
4. The ROI should include as much as possible of the area of the nodule. Normal thyroid parenchyma should not be included in the ROI.
5. ROI must be placed in the nodule avoiding cystic or calcified areas as these alter the measurements. However, the use of the standard size ROI in p-SWE sometimes makes it impossible to exclude fluid and calcified areas of a nodule.
6. Choosing a correct preset is important to acquire accurate measurements, and the preset should be 0–180 kPa for the thyroid application. Increase the elasticity color gain to its maximum till the noise starts to appear in the elasticity image, because this will aid in acquiring good color sensitivity elastograms.
7. With 2D-SWE in order to obtain the most significant quantitative readouts, ROIs should be placed on the stiffest part of a lesion as shown in the velocity map (2D-SWE elastogram). Malignancy is often very heterogeneous in stiffness; it is useful to choose the stiffest site for the measurement.
8. In the elasticity image, there can be areas with no color that may be due to fluid content, calcification, or impossible velocities’measurements due to technical problems. In some systems the displayed measurements show “X.XX” or “0.00” because these nodules contain cysts and calcifications. Cysts, when containing nonviscous fluids, do not support shear waves, and so they appear as color voids, usually seen as black regions where the anechoic B-mode layer shows through. On the other hand, when the cyst fluid is viscous, shear wave signals may be seen and would display a soft region.
9. With p-SWE, sometimes the system cannot calculate an accurate measurement due to a variety of factors such as motion or noise or probably a too low amplitude of the generated shear wave or even too high stiffness in the nodule with a too high shear wave speed that cannot be sampled. ARFI for example, when it cannot yield a measurement, displays “X.XX m/s” instead of the expected numeric value. In such an occurrence,slightly change the position of the probe and repeat the evaluation.
11. Always bear in mind that, as with strain elastography, malignancy may appear genuinely soft, albeit rarely. Follicular carcinomas, in particular, can be soft and difficult to distinguish from benign nodules.
12. For good documentation, some authors recommend, for every nodule, the acquisition of three cine loops, each of at least 10 s of duration.
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