Human Observer Sensitivity to Temporal Noise During B-Mode Ultrasound Scanning: Characterization and Imaging Implications.

This work measures temporal signal-to-noise ratio (SNR) thresholds that indicate when random noise during ultrasound scanning becomes imperceptible to expert human observers. Visible noise compromises image quality and can potentially lead to non-diagnostic scans. Noise can arise from both stable acoustic sources (clutter) or randomly varying electronic sources (temporal noise). Extensive engineering effort has focused on decreasing noise in both of these categories. In this work, an observer study with five practicing sonographers was performed to assess sonographer sensitivity to temporal noise in ultrasound cine clips. Understanding the conditions where temporal noise is no longer visible during ultrasound imaging can inform engineering efforts seeking to minimize the impact this noise has on image quality. The sonographers were presented with paired temporal noise-free and noise-added simulated speckle cine clips and asked to select the noise-added clips. The degree of motion in the imaging target was found to have a significant effect on the SNR levels where noise was perceived, while changing imaging frequency had little impact. At realistic in vivo motion levels, temporal noise was not perceived in cine clips at and above 28 dB SNR. In a case study presented here, the potential of adaptive intensity adjustment based on this noise perception threshold is validated in a fetal imaging scenario. This study demonstrates how noise perception thresholds can be applied to help design or tune ultrasound systems for different imaging tasks and noise conditions.

In vivo demonstration of a real-time temporal SNR acoustic output adjustment method.

This work proposes a novel method of temporal signal-to-noise ratio (SNR) guided adaptive acoustic output adjustment and demonstrates this approach during in vivo fetal imaging. Acoustic output adjustment is currently the responsibility of sonographers, but ultrasound safety studies show recommended ALARA (As Low As Reasonably Achievable) practices are inconsistently followed. This study explores an automated ALARA method that adjusts the Mechanical Index (MI) output, targeting imaging conditions matching the temporal noise perception threshold. A 28 dB threshold SNR is used as the target SNR, following prior work showing relevant noise quantities are imperceptible once this image data quality level is reached. After implementing adaptive output adjustment on a clinical system, the average MI required to achieve 28 dB SNR in an eleven-volunteer fetal abdomen imaging test ranged from 0.17 to 0.26. The higher MI levels were required when imaging at higher frequencies. During tests with 20-second MI adjustment imaging periods, the degree of motion impacted the adaptive performance. For stationary imaging views, target SNR levels were maintained in 90% of SNR evaluations. When scanning between targets the imaging conditions were more variable, but the target SNR was still maintained in 71% of the evaluations. Given the relatively low MI recommended when performing MI adjustment and the successful adjustment of MI in response to changing imaging conditions, these results encourage adoption of adaptive acoustic output approaches guided by temporal SNR.

Validation of a sonographic checklist for the detection of histologic placenta accreta spectrum.

BACKGROUND: To standardize research terminology and to reduce unanticipated placenta accreta spectrum, the European Working Group for Abnormally Invasive Placenta developed a consensus checklist for reporting suspected placenta accreta spectrum observed during an antenatal ultrasound. The diagnostic accuracy of the European Working Group for Abnormally Invasive Placenta checklist has not been assessed. OBJECTIVE: This study aimed to test the performance of the European Working Group for Abnormally Invasive Placenta sonographic checklist in predicting histologic placenta accreta spectrum. STUDY DESIGN: This was a multisite, blinded, retrospective review of transabdominal ultrasound studies performed between 26 to 32 weeks' gestation for subjects with histologic placenta accreta spectrum between 2016 and 2020. We matched a control cohort of subjects without histologic placenta accreta spectrum in a 1:1 ratio. To reduce reader bias, we matched the control cohort for known risk factors including previa, number of previous cesarean deliveries, previous dilation and curettage, in vitro fertilization, and clinical factors affecting image quality including multiple gestation, body mass index, and gestational age at the ultrasound. Nine sonologists from 5 referral centers, blinded to the histologic outcomes, interpreted the randomized ultrasound studies using the European Working Group for Abnormally Invasive Placenta checklist. The primary outcome was the sensitivity and specificity of the checklist to predict placenta accreta spectrum. Two separate sensitivity analyses were performed. First, we excluded subjects with mild disease (ie, only assessed subjects with histologic increta and percreta). Second, we excluded interpretations from the 2 most junior sonologists. RESULTS: A total of 78 subjects were included (39 placenta accreta spectrum, 39 matched control). Clinical risk factors and image quality markers were statistically similar between the cohorts. The checklist sensitivity (95% confidence interval) was 76.6% (63.4-90.6) and the specificity (95% confidence interval) was 92.0% (63.4-99.9) with a positive and negative likelihood ratio of 9.6 and 0.3, respectively. When we excluded subjects with mild placenta accreta spectrum disease, the sensitivity (95% confidence interval) increased to 84.7% (73.6-96.4) and the specificity was unchanged at 92.0% (83.2-99.9). Sensitivity and specificity were unchanged when the interpretations from the 2 most junior sonologists were excluded. CONCLUSION: The 2016 European Working Group for Abnormally Invasive Placenta checklist for interpreting placenta accreta spectrum has a reasonable performance in detecting histologic placenta accreta spectrum and excluding cases without placenta accreta spectum.

An Automated Region-Selection Method for Adaptive ALARA Ultrasound Imaging.

The objective of this work was to develop an automated region of the interest selection method to use for adaptive imaging. The as low as reasonably achievable (ALARA) principle is the recommended framework for setting the output level of diagnostic ultrasound devices, but studies suggest that it is not broadly observed. One way to address this would be to adjust output settings automatically based on image quality feedback, but a missing link is determining how and where to interrogate the image quality. This work provides a method of region of interest selection based on standard, envelope-detected image data that are readily available on ultrasound scanners. Image brightness, the standard deviation of the brightness values, the speckle signal-to-noise ratio, and frame-to-frame correlation were considered as image characteristics to serve as the basis for this selection method. Region selection with these filters was compared to results from image quality assessment at multiple acoustic output levels. After selecting the filter values based on data from 25 subjects, testing on ten reserved subjects' data produced a positive predictive value of 94% using image brightness, the speckle signal-to-noise ratio, and frame-to-frame correlation. The best case filter values for using only image brightness and speckle signal-to-noise ratio had a positive predictive value of 97%. These results suggest that these simple methods of filtering could select reliable regions of interest during live scanning to facilitate adaptive ALARA imaging.

A prospective blinded comparison of second trimester fetal measurements by expert and novice readers using low-cost novice-acquired 3D volumetric ultrasound.

RATIONALE AND OBJECTIVES: Two-dimensional (2D) ultrasound (US) is operator dependent, requiring operator skill and experience to selectively identify and record planes of interest for subsequent interpretation. This limits the utility of US in settings in which expert sonographers are unavailable. Three-dimensional (3D) US acquisition of an anatomic target, which enables reconstruction of any plane through the acquired volume, might reduce operator dependence by providing any desired image plane for interpretation, without identification of target planes of interest at the time of acquisition. We applied a low-cost 3DUS technology because of the wider potential application compared with dedicated 3DUS systems. We chose second trimester fetal biometric parameters for study because of their importance in maternal-fetal health globally. We hypothesized that expert and novice interpretations of novice-acquired 3D volumes would not differ from each other nor from expert measurements of expert-acquired 2D images, the clinical reference standard. MATERIALS AND METHODS: This was a prospective, blinded, observational study. Expert sonographers blinded to 3DUS volumes acquired 2DUS images of second trimester fetuses from 32 subjects, and expert readers performed interpretation, during usual care. A novice sonographer blinded to other clinical data acquired oriented 3DUS image volumes of the same subjects on the same date. Expert readers blinded to other data assessed placental location (PL), fetal presentation (FP), and amniotic fluid volume (AFV) in novice-acquired 3D volumes. Novice and expert raters blinded to other data independently measured biparietal diameter (BPD), humerus length (HL), and femur length (FL) for each fetus from novice-acquired 3D volumes. Corresponding gestational age (GA) estimates were calculated. Inter-rater reliability of measurements and GAs (expert 3D versus expert 2D, novice 3D versus expert 2D, and expert 3D versus novice 3D) were assessed by intraclass correlation coefficient (ICC). Mean inter-rater measurement differences were analyzed using one-way ANOVA. RESULTS: 3D volume acquisition and reconstruction required mean 30.4 s (±5.7) and 70.0 s (±24.0), respectively. PL, FP, and AFV were evaluated from volumes for all subjects; mean time for evaluation was 16 s (±0.0). PL, FP, and AFV could be evaluated for all subjects. At least one biometric measurement was possible for 31 subjects (97%). Agreement between rater pairs for a composite of all measures was excellent (ICCs ≥ 0.95), and for individual measures was good to excellent (ICCs ≥ 0.75). Inter-rater differences were not significant (p > .05). CONCLUSIONS: Expert and novice interpretations of novice-acquired 3DUS volumes of second trimester fetuses provided reliable biometric measures compared with expert interpretation of expert-acquired 2DUS images. 3DUS volume acquisition with a low-cost system may reduce operator dependence of ultrasound.

Medical and surgical treatment of placenta percreta to optimize bladder preservation.

BACKGROUND: Placenta percreta is associated with significant morbidity and mortality. Interventions are dictated by hemodynamic stability, desire to retain future fertility, and efforts to reduce surgical morbidity at time of delivery. CASES: Two cases of antenatally diagnosed placenta percreta with bladder invasion are presented. Conservative management was used, including endovascular interventions, leaving the placenta in situ, methotrexate, and delayed hysterectomy. Postoperative outcomes were acceptable, with no significant hemorrhagic complications or need for extensive bladder reconstruction. CONCLUSION: Antenatal diagnosis of placenta percreta with bladder invasion is essential in the multidisciplinary management of this potentially catastrophic condition. A comprehensive approach including delayed hysterectomy after medical management resulted in an excellent clinical outcome.

Multidisciplinary approach to manage antenatally suspected placenta percreta: updated algorithm and patient outcomes.

BACKGROUND: Due to the significant morbidity and mortality associated with placenta percreta, alternative management options are needed. Beginning in 2005, our institution implemented a multidisciplinary strategy to patients with suspected placenta percreta. The purpose of this study is to present our current strategy, maternal morbidity and outcomes of patients treated by our approach. METHODS: From 2005 to 2014, a retrospective cohort study of patients with suspected placenta percreta at an academic tertiary care institution was performed. Treatment modalities included immediate hysterectomy at the time of cesarean section (CHYS), planned delayed hysterectomy (interval hysterectomy 6 weeks after delivery) (DH), and fertility sparing (uterine conservation) (FS). Prognostic factors of maternal morbidity were identified from medical records. Complications directly related to interventional procedures and DH was recorded. Descriptive statistics were utilized. RESULTS: Of the 21 patients with suspected placenta percreta, 7 underwent CHYS, 13 underwent DH, and 1 had FS with uterine preservation. Of the 20 cases that underwent hysterectomy, final pathology showed 11 increta, 7 percreta, and 2 inconclusive. 19/20 cases underwent interventional radiology (IR) procedures. Selective embolization was utilized in 14 cases (2/7 CHYS; 12/13 DH). The median time from cesarean section (CS) to DH was 41 [26-68] days. There were no cases of emergent hysterectomy, delayed hemorrhage, or sepsis in the DH group. Both estimated blood loss and number of packed red blood cell transfusions were significantly higher in the CHYS group. 3/21 cases required massive transfusion (2 CHYS, 1 FS) with median total blood product transfusion of 13 units [12-15]. The four IR-related complications occurred in the DH group. Incidence of postoperative complications was similar between both groups. Median hospital length of stay (LOS) after CHYS was 4 days [3-8] compared to DH cohort: 7 days [3-33] after CS and 4 days [1 -10] after DH. The DH cohort had a higher rate of hospital readmission of 54% (7/13) compared to 14% (1/7) CHYS, most commonly due to pain. There were no maternal deaths. CONCLUSION: This multidisciplinary strategy may appear feasible; however, further investigation is warranted to evaluate the effectiveness of alternative approaches to cesarean hysterectomy in cases of morbidly adherent placenta.

Prenatal diagnosis of a trauma-related fetal epidural hematoma.

BACKGROUND: Prenatal diagnosis of fetal intracranial hemorrhage has important etiologic, management, and prognostic implications. Ultrasonography and magnetic resonance imaging (MRI) have been used to identify and evaluate this condition. We present the first reported case of epidural hematoma diagnosed prenatally. CASE: A 25-year-old para 3 was referred for evaluation of a suspected fetal intracranial abnormality following an alleged assault. Ultrasonography and MRI were used to diagnose an epidural hematoma prenatally. The fetus subsequently died in utero. Autopsy confirmed the presence of an epidural hematoma. CONCLUSION: Ultrasonography and MRI were useful in diagnosing a fetal epidural hematoma. Unfortunately, no known effective in utero therapy exists for this rare problem.

Preterm premature rupture of membrane management--inpatient versus outpatient: a retrospective review.

The purpose of this study was to evaluate the outcome of patients with preterm premature rupture of membranes (PPROM) managed as inpatients who would have been candidates for outpatient management by prior published criteria. A retrospective review of medical records of PPROM subjects enrolled in a prospective cohort study was performed. Similar criteria to those established in a randomized trial for home management of PPROM by Carlan et al were applied. Assuming local residence, 65 subjects met the criteria for outpatient management. Demographic and delivery information were collected. Of the 65 subjects, 12 (18%) delivered <2 hours from the sentinel event. Adverse outcomes in these 12 subjects could have been devastating had they been managed as outpatients. Given the susceptibility of these subjects to obstetric emergencies, patients with PPROM at a viable gestational age should be considered for management as inpatients in a tertiary-care facility.

First trimester screening.

Screening for aneuploidy has traditionally been reserved for women of advanced maternal age. More recent advances in serum screening and ultrasound technology have allowed women of all ages to be offered screening in the second and even first trimester. These methods and their effectiveness are discussed.