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Original Research |
1 Department of Radiology, Breast Imaging Division, Duke University Medical
Center, Box 3808, 2nd Fl., Red Zone, South Hospital, Durham, NC 27710.
2 Present address: Seattle Cancer Care Alliance, Seattle, WA 98109-1023.
3 Siemens Medical Solutions, USA, Inc., Issaquah, WA 98029.
4 Biomedical Engineering, Duke University Medical Center, Durham, NC
27708.
Received January 3, 2005;
accepted after revision March 9, 2005.
Financial support provided by Siemens Medical Solutions USA, Inc.
Abstract
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SUBJECTS AND METHODS. Thirty-nine lesions—11 simple cysts and seven solid masses (control group) and 21 masses with indeterminate findings for the diagnosis of a cyst versus a solid lesion (study group)—in 34 patients were evaluated using streaming detection. All lesions underwent cyst aspiration or biopsy (n = 35) or were diagnosed simple cysts (n = 4) on sonography. Lesion size and depth were recorded. Streaming detection software was placed on conventional sonography units. Acoustic pulses were focused on the lesion, and if fluid movement was generated, it was seen on the spectral Doppler display as velocity away from the transducer. Lesions were then aspirated or underwent biopsy, and the viscosity of the aspirated fluid was recorded. The sensitivity and specificity of the technique and the effect of cyst size, cyst depth, and fluid viscosity in diagnosing fluid-filled cysts were assessed.
RESULTS. Overall, 31 cysts and eight solid masses (seven benign, one carcinoma) were diagnosed in the study and control groups. Aspiration of indeterminate lesions resulted in 20 cysts and one solid mass. Lesions ranged in size from 4 to 47 mm and in depth from 4 to 29 mm. In the control group, streaming detection correctly showed nine of the 11 simple cysts (sensitivity, 82%; positive predictive value, 100%), and acoustic streaming was absent in all seven solid masses (specificity, 100%; negative predictive value, 78%). Of the indeterminate lesions, streaming detection allowed correct identification of 10 of 20 cysts (sensitivity, 50%; positive predictive value, 100%). Acoustic streaming was not detected in the one solid study group lesion. Neither cyst size or depth nor fluid viscosity had a significant effect on the ability to detect fluid.
CONCLUSION. The streaming detection technique improved differentiation of cysts from solid masses in indeterminate lesions and has potential for reducing the number of recommended cyst aspirations for the diagnosis of indeterminate breast masses.
Keywords: biopsy • breast • breast cancer • Doppler sonography • sonography • streaming detection
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The management of indeterminate lesions that are thought to represent complicated cysts varies among practices. Some practices rely on aspiration to confirm the diagnosis, whereas others recommend 6-month follow-up imaging given the low likelihood of malignancy [1]. In the guidance chapter of the BI-RADS Atlas [7], nonpalpable complicated cysts are placed in the final assessment category 3, with recommendation for short-term follow-up, whereas palpable complicated cysts are listed in the final assessment category 4A, for which intervention is recommended [8]. Regardless of the management strategy suggested, these lesions create anxiety for patients, and both short-term follow-up imaging and aspiration add to the health care costs for the process of early breast cancer detection.
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All lesions were identified during diagnostic mammography and sonography either by one of six breast imaging radiologists at our institution (n = 36) or by a radiologist at an outside institution (n = 3). Streaming detection was performed on each lesion by one of four dedicated breast imaging radiologists (referred to hereafter as "study radiologists") before aspiration or core biopsy of the lesion (n = 35) or after evaluation of the four simple cysts that were not aspirated. Each study radiologist had previously been trained to use the streaming software technique initially on phantoms that contained both cysts and solid lesions, and later on lesions in patients during an approved software development trial.
The streaming detection software (Siemens Medical Solutions) was initially downloaded onto two sonography units (Sonoline Elegra, Siemens Medical Solutions) that would be used for imaging guidance of cyst aspirations and core needle biopsies. The study radiologist using sonography measured each lesion in the radial and antiradial orientations with respect to the nipple and in the anterior-to-posterior dimension. In addition, the depth of the lesion was measured from the skin surface to the center of the lesion. The lesion was also evaluated for the presence of color or power Doppler signal within or immediately around the lesion.
The streaming detection software display included a combined B-mode image and color and spectral Doppler modes with a Doppler tracing function with an adjustable gate that could be directed over the lesion (Figs. 1A, 1B, 2A, 2B, 3A, and 3B). To acquire streaming data about each lesion, the streaming detection software was activated and the lesion was identified using the B-mode technique. The suspicious breast mass was then imaged in its largest cross section possible and positioned within the color Doppler box. The spectral Doppler cursor was positioned on the screen within the cyst near the distal wall and then up to eight acquisitions were performed to evaluate each lesion. During a single acquisition, initiated by pushing a button, Doppler pulses were focused within the lesion, and the sonography screen displayed both a resulting Doppler wave signal and color Doppler B-mode image (Figs. 1A, 1B, 2A, and 2B). Each sequence lasted 250 msec. The sequences consisted of high-energy "pushing" beams that were processed with conventional Doppler methods interspersed with B-mode and color Doppler beams, which were also processed conventionally.
All delivered energy was approved by scientists with the U.S. Food and Drug Administration (FDA) as being a nonsignificant risk, and a letter to that effect was obtained from the FDA [10]. Both the Doppler wave signal and color Doppler B-mode image were recorded for each acquisition. In real time during each acquisition, the study radiologist ascertained whether the displayed image showed a Doppler tracing below the baseline—representing a positive signal (streaming was present) (Figs. 1A, 1B, 2A, and 2B)—or was indeterminate for or showed no Doppler signal below the baseline (negative for streaming) (Figs. 3A and 3B).
Four to eight acquisitions were obtained for each lesion. The entire process of acquiring and evaluating the image, recording the results, and adjusting the transducer for subsequent acquisitions generally took less than 5 min for eight acquisitions. Multiple acquisitions were made because many variables, such as beam position within the lesion, transducer motion, and transmit focal depth, can affect the generated streaming velocity and its detection [9]. However, because acoustic streaming by definition cannot be detected in solid lesions, detection of acoustic streaming on just one trial acquisition was considered positive for a cyst in our study. If the lesion showed acoustic streaming within the first four acquisitions, no more were performed. If acoustic streaming was not seen in any of the first four acquisitions, up to four additional acquisitions were performed for a maximum of eight acquisitions. At the completion of the streaming detection acquisitions and before the aspiration or biopsy procedure, the study radiologist recorded a final assessment of the presence or absence of acoustic streaming (fluid movement) within the lesion based on the presence of one positive result in four to eight acquisitions.
Cyst aspiration procedures were performed on all cysts or indeterminate lesions scheduled for aspiration using an 18-gauge needle with the free-hand technique under sonographic guidance. Lesions with nonbloody fluid aspirated to complete resolution with no identifiable residual fluid and no suggestion of a solid component underwent no further intervention. Because more viscous fluid requires a larger force to induce detectable streaming velocities [11], the viscosity of the aspirated fluid was evaluated subjectively on a scale of 1–5 by the radiologist, based on the study radiologists' previous clinical experience with cyst aspiration (1 = least viscous, like water; 5 = most viscous, like toothpaste), before it was discarded.
For lesions containing bloody fluid that was submitted for cytologic evaluation, a marker clip (CorMark, Artemis Medical) was introduced at the site of the lesion. Lesions that were incompletely aspirated or that were determined to be solid during the initial cyst aspiration attempt then underwent core needle biopsy. Large core needle biopsies were performed on these and all solid masses using a 14-gauge needle (Achieve, Allegiance) with or without coaxial introducer needle (Bard Coaxial Biopsy Needle, C.R. Bard). Five core samples were obtained from each solid mass, and if a lesion was poorly seen after the biopsy, a biopsy marker clip was placed. For each lesion submitted for cytologic or histologic evaluation, the results were recorded and correlated with streaming data.
The sensitivity, specificity, and positive and negative predictive values of streaming detection in diagnosing fluid-filled cysts in both the control population of cysts and solid masses and the study population of indeterminate lesions were assessed. In addition, a Wilcoxon's–Mann-Whitney test and a paired Student's t test were used to compare the viscosity, size, and depth of indeterminate lesions correctly classified as cysts by the streaming technique to those incorrectly classified.
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Seven simple cysts (64%) underwent aspiration either for clinical symptoms or at the patient's request, and four (36%) were not aspirated, on the basis of the sonographic diagnosis of a simple cyst. All cysts were aspirated to complete resolution. Core biopsies of the seven solid masses revealed one malignant lesion (invasive ductal carcinoma) (14%), three fibroadenomas (43%), one papilloma (14%), and two benign regions of fibrosis and fibrocystic change (29%), each correlating with the respective solid mass.
In the control group, streaming detection was positive for fluid movement and correctly identified nine (82%) of 11 simple cysts (Figs. 1A and 1B), with a sensitivity and positive predictive value for a cyst of 82% and 100%, respectively. The two simple cysts that did not show acoustic streaming were completely aspirated. The specificity and negative predictive value of the control group were 100% and 78%, respectively, with acoustic streaming absent in all solid lesions (Figs. 3A and 3B).
Study Group of Indeterminate Masses
Twenty-one lesions indeterminate for a cyst versus a solid mass on
preliminary B-mode sonography in 19 patients (age range, 41–69 years;
mean age, 50 years) were evaluated with acoustic streaming
(Table 1). Lesions ranged in
size from 4 to 24 mm (mean, 10.8 mm; median, 9 mm) in greatest radial or
antiradial orientation, in size from 3 to 10.6 mm (mean, 5.9 mm; median, 5 mm)
in anterior-to-posterior dimension, and in depth from 4 to 28.8 mm (mean, 16.3
mm; median, 16.7 mm).
Eighteen lesions (86%) were aspirated to complete resolution, two (9%) were incompletely aspirated, and one (5%) was determined to be solid. Core biopsies of the latter three lesions showed findings consistent with a cyst wall in the two partly aspirated cysts and a fibroadenoma correlating with the solid mass. Bloody cyst fluid in three (17%) of the 18 completely aspirated lesions was sent for cytologic evaluation: negative findings were reported for two and the third showed cytologic atypia. Subsequent surgical excision of the lesion with atypia was benign. Overall, all lesions were benign with 20 lesions (95%) determined to be cysts and one (5%), a solid mass. The mean viscosity of the cysts as determined by subjective inspection of the fluid was 2.3 (viscosity range, 1–5; median, 2).
Streaming detection was positive for fluid movement during at least one acquisition (Table 1) and therefore correctly identified in 10 of 20 cysts in the study population of indeterminate lesions (Figs. 2A and 2B), with a sensitivity and positive predictive value for a cyst of 50% and 100%, respectively. Acoustic streaming did not occur in the one solid lesion in the population, resulting in a specificity of 100%. However, given the small number of solid lesions, the negative predictive value was only 9% in this group of indeterminate lesions.
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Our study evaluated streaming detection for indeterminate lesions thought to be complicated cysts and for simple cysts and solid masses. Complex masses were excluded from our study, and streaming detection is not recommended for evaluating complex masses. To avoid confusion in the terminology, the current definitions of the terms "complicated cyst" and "complex cyst" should be clearly distinguished and emphasized at this point. In the past, the term "complex cyst" had been used to refer to lesions meeting some but not all of the criteria for simple cysts, with "complicated cyst" being a specific subset of this group [1]. However, the 2003 American College of Radiology BI-RADS lexicon classification form for sonography update the specific descriptions of each type of lesion [7]. Complicated cysts are cysts "most commonly characterized by homogeneous low-level internal echoes. Complicated cysts may also have fluid–fluid, or fluid–debris levels that may shift with changes in patient's position" [7]. Complex masses, on the other hand, are defined in the same manual as masses that "contain both anechoic and echogenic components," referring to partly fluid filled and partly solid masses [12]. These masses are managed more aggressively than complicated cysts because they have a 42% prevalence of malignancy [1, 13]; in our practice, complex masses undergo either core biopsy of the solid component or excisional biopsy of the entire lesion because the solid component is viewed with suspicion.
Streaming detection is not recommended for evaluating complex masses because detection of cyst fluid would not alter the management of the solid component of the complex mass. Likewise, this technique is not recommended for irregular masses, those with ill-defined or spiculated margins, those that are taller than they are wide, or any lesion that has other features suggestive of malignancy. Biopsy would be recommended for such lesions to exclude malignancy, and streaming detection would have no role in evaluating these lesions.
Streaming detection is an ultrasonic method that uses acoustic energy to induce fluid flow or acoustic streaming in cyst fluid, with flowing fluid detected using Doppler methods. The fluid motion is caused by the absorption of acoustic energy in the fluid, exerting a force that pushes the fluid in the direction of wave propagation, away from the transducer. Fluid velocities that reach a specified threshold are then detected and displayed as acoustic streaming. Factors that can impact the generated streaming velocity during any given acquisition, and therefore have an effect on the detection of acoustic streaming using this technique, include beam position within the lesion, transducer motion, and transmit focal depth [9]. For our study, we did not evaluate the differences in streaming velocity based on these different transmit parameters; however, the following effects have been noted. Beam position within the lesion has an effect because higher streaming velocities occur when the beam is focused in the center of the cyst as opposed to the periphery of the cyst. Transducer motion reduces the amount of focused energy delivered to a given location within the cyst, thereby reducing the generated fluid velocity and likelihood of detection. Differences in transmit focal depth also have an effect on fluid velocity because, to generate comparable energy within cysts at increasing depths within the breast, the manufacturer must increase the intensity of the transmitted beams in a depth-dependent manner. Therefore, when the Doppler cursor position is changed in depth, different streaming velocities could be achieved within a given cyst, varying the result. Because of these factors, multiple acquisitions were made for each lesion in our study to increase the potential for detection of fluid flow [9].
In our pilot study, streaming detection successfully detected acoustic streaming within fluid-filled cysts in half of the indeterminate lesions recommended for cyst aspirations and showed no false-negative results in evaluating solid lesions in either the study population or the control population. Given these encouraging results, this technique has the potential to be used as a clinical tool to complement conventional breast sonography, providing an easy way for radiologists to quickly confirm that a lesion seen to be indeterminate on sonography is actually a fluid-filled cyst. Each streaming detection sequence takes less than 1 sec to be acquired and displayed on the screen for evaluation. Our study showed no false-positive acoustic streaming results in solid masses, which is critical to the success of this technique. A false-positive streaming result in a solid mass would misrepresent a lesion as a fluid-filled structure and delay the diagnosis of a solid mass. This would have potentially serious consequences if a malignant lesion were misdiagnosed as a benign cyst. Because our study evaluated only a small number of solid masses, further work evaluating larger numbers of solid masses is required to confirm the safety of this technique. A multiinstitutional study is planned for further validation of this technique.
Streaming detection has several potential advantages for clinical use. If streaming detection results were used to clinically manage the indeterminate masses in our study, which were thought to be complicated cysts on conventional B-mode sonography, then detection of acoustic streaming within these lesions would have confirmed a cyst and obviated cyst aspiration in half of the cases. The use of this technique would save patient and physician time and would help to reduce the health care costs of cyst aspiration procedures. In addition, the ability to confirm a cyst at the time of conventional sonography would also reduce patient anxiety related to the lesion and spare the patient the discomfort of undergoing an aspiration procedure.
The software for this technique is incorporated into a conventional sonography unit, with no additional space-occupying equipment required, and streaming detection software requires only the push of a button for each acquisition, with results seen immediately in real time on the screen. Little training would be required for a radiologist to position the Doppler cursor over the lesion and identify acoustic streaming within the mass, displayed as a Doppler tracing below the baseline.
Although streaming detection has the potential to diagnose cysts in up to 50% of indeterminate lesions based on our pilot data, half of the indeterminate lesions that were proven to be cysts at aspiration did not exhibit acoustic streaming and were considered false-negatives. Because streaming velocity has been shown to be dependent on the amount of acoustic energy, the size of the cyst [11], the viscosity of the cyst fluid, and lesion depth, we evaluated some of these variables with regard to their effect on acoustic streaming detection in cysts. Lesion size, lesion depth, and fluid viscosity were recorded and compared in the cysts that showed versus those that did not show acoustic streaming to determine whether these factors played a role in acoustic streaming detection. In our small pilot population, a significant difference in detection of acoustic streaming was not found to relate to these three factors; therefore, a specific subset of complicated cysts for which streaming detection would be most useful based on size, depth, or viscosity was not identified. However, a fourth factor that was not evaluated in our study might have an influence on these results. Differences in the attenuation properties of the breast tissue located between the transducer and the cyst would result in different energies being applied to the cyst fluid— for example, fatty tissue would cause greater attenuation than fibroglandular tissue and therefore result in lower generated velocities and reduced streaming detection. This factor will be considered in future studies.
In conclusion, streaming detection in our study improved the detection of cysts in a population of indeterminate complicated cysts found on conventional B-mode sonography. For these lesions that have a low likelihood of malignancy, our pilot study results are encouraging in that this technique has the potential to change the paradigm for managing complicated cysts because some lesions would be diagnosed as benign immediately and require no further intervention or follow-up. However, before streaming detection can enter routine clinical use, a much larger multiinstitutional study is necessary and is planned for further evaluation of this technique.
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