O-RADS US: Scanning Technique and Doppler Color Score
Why a Separate Technical Protocol
O-RADS US begins not with the selection of a category but with obtaining diagnostic images. In the ACR O-RADS US v2022 Technical Guidance, the technical section is separated from the risk stratification itself: the task of the ultrasound physician is to show the anatomical location of the lesion, its internal structure, surface, solid elements, and vascularity so that the subsequent category is reproducible.
Insufficient depth, excessive smoothing, improperly set color gain, or too large a color scale most often lead to two errors: missing weak blood flow and falsely elevating vascularization due to artifacts. Therefore, the protocol should capture not only aesthetically pleasing static images but also those features on which the O-RADS lexicon depends.
Access: Transvaginal, Transabdominal, or Combined
The basic method for most adnexal lesions is transvaginal ultrasound with a high-frequency probe with sufficient penetration depth. Transabdominal access is added if the lesion is large, located high, extends beyond the field of the transvaginal probe, or if there is a need to assess spread beyond the pelvis.
Combined examination is especially important for large cystic-solid lesions: transvaginal access better shows the internal architecture, while transabdominal access shows the complete external contour, cranial pole, and relationships with the uterus, bladder, and intestines.
Grayscale Setting: Anatomy First, Then Lexicon
Before turning on the Doppler, a quality B-image must be obtained. Depth, focus, gain, and dynamic range are adjusted so that the wall, septa, internal contour, and possible solid components are visible. The lesion should not be assessed in just one plane: the adnexa and finding are documented in at least two mutually perpendicular planes, and the lesion sizes in three orthogonal dimensions.
If the lesion occupies almost the entire screen, the scale should be reduced or another access should be used; otherwise, the maximum diameter may be underestimated, and external irregularities may be missed. Conversely, if the object is small, magnification should allow differentiation of the wall, thin septa, and small intracavitary protrusions.
What Must Be Shown in Images
| Protocol Element | What to Document | Why for O-RADS US |
|---|---|---|
| Localization | Right/left adnexa, connection with ovary, uterus, or tube | Helps distinguish ovarian from extraovarian lesions |
| Size | 3 orthogonal dimensions of the entire lesion | Needed for description, dynamics, and routing |
| Wall and Septa | Smoothness, thickening, irregularities, number of chambers per lexicon | Determine the morphological type of the lesion |
| Solid Elements | Presence, shape, maximum protrusion, connection with wall or septum | Critical for distinguishing cystic from cystic-solid findings |
| Papillary Projections | Solid protrusion into the cyst cavity with a height ≥3 mm | One of the key features of the O-RADS lexicon |
| Blood Flow | Color score 1–4 in the most vascular area | Affects the assessment of solid and cystic-solid lesions |
| Extraovarian Signs | Free fluid, ascites, peritoneal or omental nodules if present | Change the clinical interpretation of the study |
How to Measure the Lesion and Solid Components
The main size is not the size of a single chamber but the maximum size of the entire lesion with two perpendicular dimensions. For a multicameral cyst, the entire complex is measured, including septa and all chambers. If the lesion is not fully visible in the field of view, transabdominal access should be added rather than extrapolating the size.
The solid component is described as the tissue part of the lesion that is not a simple septum or fluid. A papillary projection according to O-RADS is a solid protrusion into the cystic cavity with a height of at least 3 mm. For reproducibility, it is useful to show this area in grayscale and with Doppler, as the presence of vascularity confirms the tissue nature, but the absence of visible flow does not negate the morphological description.
Doppler Color Score: Scale 1–4
The color score in O-RADS is a visual semi-quantitative assessment of blood flow in the wall, septa, papillary projections, or solid components. Color or power Doppler is used; it is important to assess the most vascular area, not average the picture over the entire lesion.
| Color Score | O-RADS Formulation | Practical Interpretation |
|---|---|---|
| 1 | No blood flow | No color signal with adequate setting for slow flow |
| 2 | Minimal blood flow | Single weak color signals in the wall, septum, or solid area |
| 3 | Moderate blood flow | Clear vascularity but without intensely vivid color filling |
| 4 | Very marked blood flow | Intense vascularization in the assessed component |
Doppler Setting: How Not to Underestimate or Overestimate the Score
Doppler should be activated after optimizing the grayscale. The color window should be as small as anatomy allows: it should cover the lesion and the solid area of interest, but not the entire image unnecessarily. Speed scale and filters are adjusted to detect slow flow typical for small vessels in the wall and papillary projections.
Color gain is increased until background noise appears and then slightly reduced to remove random color flashes. Too low gain gives a false color score of 1, too high causes blooming and false elevation to 3–4. Probe pressure is also important: compression can temporarily reduce blood flow, especially in small solid areas.
Power Doppler can be useful for weak flow, but it is also sensitive to patient movement, breathing, and transmitted pulsation. In case of a doubtful signal, its stability should be checked in real-time and compared with the B-image.
Where to Place the Color Assessment
The color score is assigned based on the most vascular morphologically significant component. For a simple thin-walled cyst without solid elements, the informativeness of Doppler is limited, but the absence of suspicious tissue components should be shown in grayscale. For a cystic-solid lesion, color is assessed in the papillary projection or solid tissue, not in random peripheral vessels of the ovary adjacent to the lesion.
If there are areas with different vascularity in one lesion, it is useful to indicate the maximum color score and localization in the protocol: for example, in the septum, papillary projection, or solid nodule. This makes the conclusion verifiable during repeat examination and discussion at a consilium.
Typical Technical Errors
- Assessing blood flow without prior optimization of B-mode: color appears, but it is unclear in which structure it is located.
- Too large a color scale or high filter: weak flow is not registered, forming a false score of 1.
- Excessive gain: color extends beyond tissue contours and mimics pronounced vascularization.
- Measuring only the dominant chamber instead of the entire multicameral lesion.
- Lack of transabdominal phase for a lesion that does not fit into the transvaginal field of view.
- Assigning a color score based on vessels of the normal ovary rather than the wall, septum, or solid component of the lesion.
How to Formulate a Technically Complete Conclusion
The description should separate the fact of visualization from interpretation: sizes in three planes, morphological type, presence of wall, septa, solid elements, papillary projections ≥3 mm, acoustic shadows, free fluid, and additional findings. For Doppler, indicate the color score 1–4 and the anatomical area it is based on.
If the assessment is technically limited—severe pain syndrome, inaccessibility of transvaginal access, incomplete visualization of the cranial pole, pronounced artifacts—this should be explicitly reflected. The O-RADS category is reliable only when the original images allow verification of key lexicon features.
Frequently asked questions
Is it always necessary to perform a transabdominal phase in O-RADS US?
Not always. Transvaginal access is usually primary, but transabdominal scanning is necessary if the lesion is large, located high, or not fully visible in the transvaginal probe's field of view.
Can a color score of 1 be assigned without power Doppler?
Yes, if the color Doppler is adequately optimized for slow flow and there is no signal. Power Doppler can help with weak flow but does not replace correct setting and real-time assessment.
Which area should be used for the color score in a cystic-solid lesion?
The most vascular morphologically significant area is assessed: solid component, papillary projection, wall, or septum. Peripheral vessels of the normal ovary adjacent to the lesion should not determine the score.