Auto Tissue Optimization (ATO) is a rapid, B-mode optimization feature designed to improve inter-operator image quality and reduce time necessary to optimize the image. Indirectly, these features can increase patient through-put. ATO works by creating an internal histogram of the data within a Region of Interest (ROI) and brings that ROI up to the full 256 shades of gray available, thereby enhancing the contrast. These adjustments are instantaneously made during standard B-mode scanning or can be applied to frozen, post processed images. ATO may be applied to a Harmonics image which is fundamentally different in that Harmonics imaging is created by sound interacting with tissue whereas ATO examines the data in the ROI and expands or retracts the gray scale based only on the data in the ROI.

A 43-year-old gravida 5 para 2 patient at 24.5 weeks gestation was admitted with the complaint of leaking fluid per vagina. Examination confirmed the diagnosis of spontaneous rupture of the membranes. Detailed assessment of fetal anatomy had not been done previously and therefore a scan was ordered. Assurances that there were no dysmorphic fetal features was imperative in planning the expectant management of this patient because of the risks from prolonged bedrest. The fetus was imaged with a broad bandwidth 5 MHz transducer operating between 3 and 7 MHz with and without ATO. Normal fetal anatomy was easily visualized including the presence of bilateral kidneys. Normal fetal growth was also noted.

After 3 weeks of hospitalized bedrest, the patient prolapsed the umbilical cord and underwent emergency cesarean section. After delivery the infant's anatomy was confirmed to be normal as anticipated from her ultrasound scan.

Oligohydramnios is a frequently encountered complication in obstetrics. The differential diagnosis can include spontaneous rupture of the membranes, renal agenesis and severe fetal growth restriction seen in association with dysmorphic fetuses such as in Trisomy 18. Better imaging resolution with ATO is of great value in evaluating fetal anatomy, particularly the fetal kidneys. Conventional imaging is often inadequate in this regard. Other options include an infusion of saline into the uterine cavity, but that is an invasive procedure with definite risks. Another option is magnetic resonance imaging, but maternal breathing movements often flaw the picture. Ultrasound is clearly the imaging modality of choice and, by using ATO, we have been able to demonstrate the fine resolution and anatomic evaluation required in managing this patient. ATO was applied throughout most of the real-time exam but was also used on frozen images and post processing. Clearly, better resolution leading to faster management decisions will improve patient through-put.

Image 1a: Without ATO.	Image 1b: With ATO - the intracranial structures are well defined.

Image 2a: Without ATO.	Image 2b: With ATO - normal bilateral kidneys seen which excludes the diagnosis of renal agenesis.

Image 3a: Without ATO.	Image 3b: With ATO - note the detail seen in the fetal heart when ATO is applied.

Conclusion

ATO has distinct advantages over conventional high frequency imaging when oligohydramnios is encountered because it optimizes the gray scale within the Region of Interest.

Print copies of these clinical papers are available from GE. Many of the figures are easier to read on the print copies than they are here. To receive your own copy, send email to GE and reference publication number 98-5425.