渡部 多佳子¹, 石田 秀明¹, 小松田 智也¹, 古川 佳代子¹, 長沼 裕子²

Takako WATANABE¹, Hideaki ISHIDA¹, Tomoya KOMATSUDA¹, Kayoko FURUKAWA¹, Hiroko NAGANUMA²

¹秋田赤十字病院超音波センター, ²市立横手病院内科

¹Center of Diagnostic Ultrasound, Akita Red Cross Hospital, ²Department of Internal Medicine, Yokote Municipal Hospital

キーワード : mass screening, ultrasound, acoustic velocity, 3D, trapezoid

腹部超音波集検は“mass-screening”の一環として行われることが多い．この20年超音波工学の進歩は目覚しいが，この進歩が集検用の装置に改革をもたらしたことは無く，安価な装置でなされてきた．やはり，精度向上のため，我々の腹部超音波集検用装置についての認識もそろそろ変えなくてはいけない時期になっているのではないだろうか．この目的に沿っていると思われる幾つかの技術をここで述べる．1）音速補正法：超音波画像作成のための現行装置が使用している〔体内の音速伝播速度は一定である〕非現実的過程を補正する試みである．伝播時間から対象までの距離を算出する際の仮定伝播速度を変化させる方式では，距離方向の画質向上が期待出来る．一方，超音波を幅広い“zone”で放射し多数の素子で反射信号を受信，その整合性を検討する方式（zone sonography）では方位分解能の向上が期待出来る．2）視野角可変方式：Trapezoid scanningに見られるように視野角を変化させることで解剖学的オリエンテーションがつきやすくなる．3）装置の小型化：コンピューター技術の進歩に伴い可能とはなるが，画質の劣化や操作性の低下は避ける必要がある．4）3D：3Dは位置認識が正確となり急速に普及してきた．これにより，多方向からの検討や正確な測定が容易となりつつある．まとめ：以上のような技術の取り込みも超音波集検用装置にとって考慮すべき時期となっている．

Abdominal ultrasound has been used in general screening in Japan for the past 20 years, during which medical ultrasound instrumentation has rarely benefited from advanced ultrasound technology: Moderate or low-priced systems have always been used. We now need to be more aware of the operational principles of our ultrasound equipment in order to improve diagnostic confidence. We discuss technologies that show promise for this purpose. 1) Acoustic velocity adjustment: All actual ultrasound systems reconstruct ultrasound images on the assumption that ultrasound propagates through the body at a fixed velocity of 1530 to 1540 m/sec, and the discordance between actual propagation velocity in tissue and the assumed propagation velocity makes ultrasound images ambiguous. An acoustic velocity adjustment system can present many images simultaneously in a variety of ways by changing the back-ground acoustic velocity. There are two types of systems: a) one using conventional line-by-line sonography, which is expected to improve distal resolution, and b) one employing zone sonography, which is designed to increase lateral resolution. 2) Trapezoid scanning: This system widens the scanning plane. The probe is operated by applying voltage pulses to all elements in the assembly as a complete group, but with small time differences. The same time differences are used in each scan and the process is repeated. Beam direction is adjusted by slight angulation from scan to scan. Advances in computer technology have expanded the possibilities for generating uniform beamforming. Trapezoid scanning provides certain advantages, especially the ability to facilitate anatomical orientation. 3) Small devices: Advances in computer technology will expand the possibilities for minimizing instrument size without degrading image quality or image display capabilities. 4) 3D: A series of 2D images are recorded rapidly while the conventional probe is manipulated over the area of interest. 2D ultrasound images are generated while the probe is moved, and are integrated at predefined positional intervals to avoid geometric distortion. 3D ultrasound offers definite benefits, and integrated views obtained with 3D ultrasound may permit better and faster understanding of the whole structure of the abdomen and thus facilitate a more accurate diagnosis. Navigating the abdominal vessels in three orthogonal planes of a section enables the operator to facilitate correct determination of multiple planes and standardize evaluation and measurement. Conclusion. These new technologies promise to further expand the dimension and confidence of abdominal ultrasound in mass-screening.