Miniature Ultrasound Transducer Research Articles

Low frequency (<1 MHz) transducers for intravenous sonothrombolysis

Venous embolism is a great challenge in the treatment of a wide range of diseases, including cardiovascular diseases and cancers. Ultrasound-mediated thrombolysis (sonothrombolysis) presents a promising treatment of venous embolism. In this paper, miniature ultrasound transducers with frequencies ranging from 250 kHz to 800 kHz were developed for microbubble/nanodroplet-mediated intravenous sonothrombolysis tests. Relative low frequency (e.g., <1 MHz) is preferred because of the findings that cavitation plays an important role in sonothrombolysis, and microbubble-associated cavitation events can be enhanced at low frequencies. Small aperture (e.g. <2 mm × 2 mm) low-frequency transducers are usually known with high electrical impedance (e.g., >1000 Ω), which is not preferred for efficient electromechanical transduction. To address this challenge, multilayer acoustic stacks were designed, fabricated, and characterized. The measured electrical impedance of these stacks is mostly closer to 50 Ω, and the peak negative pressure is higher than 1MPa. These small aperture transducers were then used in in vitro- thrombolysis tests with unretracted and retracted blood clots, showing promising lysis rates. Other techniques such as laser ultrasound transducers, vortex wave generation, and magnetic microbubbles were also investigated for thrombolysis tests.

Recent Advances in Transducers for Intravascular Ultrasound (IVUS) Imaging.

As a well-known medical imaging methodology, intravascular ultrasound (IVUS) imaging plays a critical role in diagnosis, treatment guidance and post-treatment assessment of coronary artery diseases. By cannulating a miniature ultrasound transducer mounted catheter into an artery, the vessel lumen opening, vessel wall morphology and other associated blood and vessel properties can be precisely assessed in IVUS imaging. Ultrasound transducer, as the key component of an IVUS system, is critical in determining the IVUS imaging performance. In recent years, a wide range of achievements in ultrasound transducers have been reported for IVUS imaging applications. Herein, a comprehensive review is given on recent advances in ultrasound transducers for IVUS imaging. Firstly, a fundamental understanding of IVUS imaging principle, evaluation parameters and IVUS catheter are summarized. Secondly, three different types of ultrasound transducers (piezoelectric ultrasound transducer, piezoelectric micromachined ultrasound transducer and capacitive micromachined ultrasound transducer) for IVUS imaging are presented. Particularly, the recent advances in piezoelectric ultrasound transducer for IVUS imaging are extensively examined according to their different working mechanisms, configurations and materials adopted. Thirdly, IVUS-based multimodality intravascular imaging of atherosclerotic plaque is discussed. Finally, summary and perspectives on the future studies are highlighted for IVUS imaging applications.

PD08-05 CAN INTRA-VESICLE ULTRASOUND SURFACE MAPPING REPLACE CYSTOSCOPY? NOVEL TECHNIQUE AND PROOF OF CONCEPT

INTRODUCTION AND OBJECTIVES:Cystoscopy remains the only acceptable method for demonstrating bladder urothelial carcinoma lesions, various imaging modalities remain unreliable for the diagnosis or follow-up. Intra-vesicle imaging with a saline filled bladder may provide better resolution. No such modality is used to date, even though small and miniature Ultrasound (US) transducers technology exists and is implemented in other medical fields. Using a robot system with mounted US transducer and surface rendering software we try to demonstrate the feasibility of a novel technique for future intra-vesicle surface mapping of the bladder.METHODS:A cylindrical construct with an internal diameter of 10 cm was 3D printed using MakerBot Replicator 2 (MakerBot Industries®), a mockup was created using bloom Gel powder, various shapes of gel protrusions representing tumors with sizes 3-50 mm were glued to the interior using molten gel.We used a linear transrectal US transducer (Hitachi EUP-U533) connected to a special ...

High-Performance Ultrasound Needle Transducer Based on Modified PMN-PT Ceramic With Ultrahigh Clamped Dielectric Permittivity.

A modified Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) polycrystalline ceramic with ultrahigh relative clamped dielectric permittivity ( ) and high piezoelectric properties ( pC/N, ) was used to fabricate high-frequency miniature ultrasound transducers. A 39-MHz high-frequency ultrasound needle transducer with a miniature aperture of 0.4 mm mm was designed and successfully characterized. The fabricated needle transducer had an electromechanical coupling factor of 0.55, large bandwidth of 80% at -6 dB, and low insertion loss of -13 dB. A wire phantom and porcine eyeball imaging study showed good imaging capability of this needle transducer. The transducer performance was found to be superior to that of other needle transducers with miniature apertures, making this modified PMN-PT ceramic-based needle transducer quite promising for minimally invasive procedures in medical applications.

Measurement of corneal tangent modulus using ultrasound indentation

Biomechanical properties are potential information for the diagnosis of corneal pathologies. An ultrasound indentation probe consisting of a load cell and a miniature ultrasound transducer as indenter was developed to detect the force–indentation relationship of the cornea. The key idea was to utilize the ultrasound transducer to compress the cornea and to ultrasonically measure the corneal deformation with the eyeball overall displacement compensated. Twelve corneal silicone phantoms were fabricated with different stiffness for the validation of measurement with reference to an extension test. In addition, fifteen fresh porcine eyes were measured by the developed system in vitro. The tangent moduli of the corneal phantoms calculated using the ultrasound indentation data agreed well with the results from the tensile test of the corresponding phantom strips (R2=0.96). The mean tangent moduli of the porcine corneas measured by the proposed method were 0.089±0.026MPa at intraocular pressure (IOP) of 15mmHg and 0.220±0.053MPa at IOP of 30mmHg, respectively. The coefficient of variation (CV) and intraclass correlation coefficient (ICC) of tangent modulus were 14.4% and 0.765 at 15mmHg, and 8.6% and 0.870 at 30mmHg, respectively. The preliminary study showed that ultrasound indentation could be applied to the measurement of corneal tangent modulus with good repeatability and improved measurement accuracy compared to conventional surface displacement-based measurement method. The ultrasound indentation can be a potential tool for the corneal biomechanical properties measurement in vivo.

Trimodality imaging system and intravascular endoscopic probe: combined optical coherence tomography, fluorescence imaging and ultrasound imaging.

In this Letter, we present a trimodality imaging system and an intravascular endoscopic probe for the detection of early-stage atherosclerotic plaques. The integrated system is able to acquire optical coherence tomography (OCT), fluorescence, and ultrasound images and simultaneously display them in real time. A trimodality intravascular endoscopic probe of 1.2 mm in diameter and 7 mm in length was fabricated based on a dual-modality optical probe that integrates OCT and fluorescence imaging functions and a miniature ultrasound transducer. The probe is capable of rotating at up to 600 rpm. Ex vivo images from rabbit aorta and human coronary arteries showed that this combined system is capable of providing high resolution, deep penetration depth and specific molecular fluorescence contrast simultaneously.

Selective gene transfer to the retina using intravitreal ultrasound irradiation.

This paper aims to evaluate the efficacy of intravitreal ultrasound (US) irradiation for green fluorescent protein (GFP) plasmid transfer into the rabbit retina using a miniature US transducer. Intravitreal US irradiation was performed by a slight modification of the transconjunctival sutureless vitrectomy system utilizing a small probe. After vitrectomy, the US probe was inserted through a scleral incision. A mixture of GFP plasmid (50 μL) and bubble liposomes (BLs; 50 μL) was injected into the vitreous cavity, and US was generated to the retina using a SonoPore 4000. The control group was not exposed to US. After 72 h, the gene-transfer efficiency was quantified by counting the number of GFP-positive cells. The retinas that received plasmid, BL, and US showed a significant increase in the number (average ± SEM) of GFP-positive cells (32 ± 4.9; n = 7; P < 0.01 ). No GFP-positive cells were observed in the control eyes (n = 7). Intravitreal retinal US irradiation can transfer the GFP plasmid into the retina without causing any apparent damage. This procedure could be used to transfer genes and drugs directly to the retina and therefore has potential therapeutic value.

Characterization of an epoxy filler for piezocomposites compatible with microfabrication processes [Correspondence

Miniature ultrasound transducer arrays that can operate at frequencies above 30 MHz are needed for high-resolution medical imaging. One way to achieve this is with a kerfless structure based on 1-3 connectivity piezocomposite with the electrodes defined by photolithography. To achieve this, not only does the composite need planar, parallel, and smooth surfaces, but it must also be made with an epoxy filler compatible with the chemicals, heat, and vacuum required for photolithography. This paper reports full characterization of an epoxy suitable for fine-scale kerfless array fabrication, including photolithographic processing. Material properties have been investigated as a function of cure temperature and for compatibility with solvents. By increasing the cure temperature, the crosslinking between the epoxy and the hardener in- creases, resulting in a higher glass transition temperature. The cured epoxy consequently has better resistance to both heat and solvents. An elevated cure temperature, near 100°C, is required to optimize material properties for photolithography on 1-3 piezocomposites. The acoustic properties of the epoxy have also been studied. These are similar to other epoxies used in piezocomposite fabrication and no significant changes have been observed for the different cure temperatures.

Automated detection of myocardial ischaemia by epicardial miniature ultrasound transducers — a novel tool for patient monitoring during cardiac surgery☆

Early detection of myocardial ischaemia in cardiac surgery is important. We have developed an ultrasonic system for continuous myocardial monitoring by use of miniature transducers. The aim of this study was to investigate the system's ability to detect ischaemia in patients undergoing off-pump coronary artery bypass grafting (CABG), and whether automated signal analysis could detect ischaemia. In 10 patients scheduled for CABG, ultrasound transducers were fixed to the epicardium in the area supplied by left anterior descending artery (LAD), and in a remote area for control. M-mode images with measurements of wall-thickening velocities were presented in real time and systolic (S') and post-systolic velocities (PSVs) were recorded. An automated algorithm for ischaemia detection was developed, using end-systolic wall thickening as a fraction of total wall thickening. Registrations were made at baseline and during LAD occlusion. Echocardiographic strain was used as reference. Nine of 10 patients developed ischaemia during LAD occlusion, with resulting decrease in systolic and increase in post-systolic wall-thickening velocities (P<0.001). In these nine patients, Vdiff shifted below zero with no overlap between baseline and LAD occlusion (P<0.001). The automated wall-thickening fraction was reduced from 0.93±0.05 to 0.57±0.15 (P=0.001). A cut-off value of 0.85 could completely separate normal from ischaemic myocardium in all patients. The ultrasonic system detected regional ischaemia during LAD occlusion. An automated analysis algorithm demonstrated excellent ability to detect ischaemia. This technology can develop into a useful tool to detect ischaemia in cardiac surgery.

Intrauterine sonographic measurement of the embryonic brain mantle

To evaluate embryonic brain mantle measurements using intrauterine sonography in the early first trimester. In 85 women about to undergo therapeutic termination at 6-11 weeks' gestation we studied the embryonic brain mantle using a specially developed 20-MHz, flexible, catheter-based, high-resolution, real-time, miniature (1.8 mm in outer diameter) ultrasound transducer. Thickness of the embryonic brain telencephalon, diencephalon, mesencephalon and rhombencephalon was measured. We found a linear relationship between gestational age and telencephalon thickness (R(2) = 51.9%, P < 0.0001), diencephalon thickness (R(2) = 62.2%, P < 0.0001), mesencephalon thickness (R(2) = 59.2%, P < 0.0001) and rhombencephalon thickness (R(2) = 47.8%, P = 0.0043). There was also a linear relationship between crown-rump length and telencephalon thickness (R(2) = 55.0%, P < 0.0001), diencephalon thickness (R(2) = 59.6%, P < 0.0001), mesencephalon thickness (R(2) = 55.0%, P < 0.0001) and rhombencephalon thickness (R(2) = 52.3%, P = 0.0025). Embryonic brain mantle measurements by intrauterine sonography are feasible, although the invasive nature of this technique limits its usefulness in routine clinical practice. It is possible, however, that further improvement in the resolution of transvaginal sonography will allow accurate and reproducible non-invasive imaging of embryonic brain mantle development in the near future.

Drug Uptake Enhancement Using Sonodynamic Effects at 4 MHz—A Potential Application for Micro-Ultrasonic-Transducers

Sonodynamic therapy is a cancer treatment method that uses macro scale ultrasound devices to enhance the cytotoxic efficacy of anticancer drugs, such as doxorubicin [1]. In this paper, unconventional, miniature ultrasound transducers (5 mm x 5 mm x 0.5 mm) were used to create a tone-burst ultrasound (4 MHz, 32 Watt/cm(2), 20% duty cycle, 50 ms burst period). It was found that the transducer significantly (p < 0.01) enhanced the immediate cells lysis when combining with doxorubicin (20 microM) in human prostate cancer cells (PC3). With a 30-s ultrasound exposure, the immediate cell lysis and long-term cytotoxicity were enhanced by 70% and 83%, respectively, compared to controls. We have demonstrated that ultrasound in combination with doxorubicin could strongly inhibit tumour cell proliferation in vitro at lower doses of the drug. This work is a first step towards a microelectromechanical system (MEMS)-based, implantable micro-ultrasonic transducers (MUTs) that could be used in sonodynamic therapy.

OP03.02: Abnormal opercular formation on prenatal cerebral imaging: significance and correlation with fetopathological and postnatal data

studied with specially developed catheter based high-resolution, real-time miniature ultrasound transducer. Each brain mantle and secondary brain vesicles could be clearly visualized, and thickness of telencephalon, diencephalon, mesencephalon and rhombencephalon were measured. The normal range of embryonic brain mantle measurements for each day of pregnancy was determined. A linear relationships were found between the gestational age and telencephalon thickness (R2 = 51.9%), diencephalon thickness (R2 = 62.2%), mesencephalon thickness (R2 = 59.2%), and rhombencephalon thickness (R2 = 47.8%), respectively. A linear relationships were also found between the crown-rump length and telencephalon thickness (R2 = 55.0%), diencephalon thickness (R2 = 58.3%), mesencephalon thickness (R2 = 55.0%), and rhombencephalon thickness (R2 = 52.3%), respectively. These results suggest that intrauterine sonography provide an accurate embryonic brain mantle measurement value in utero. Moreover, intrauterine sonography may become an important modality in future embryonal research and in detection of embryonic brain developmental disorders in the early first-trimester pregnancy.

OP03.03: Fetal medicine physicians and the communication of ‘bad news’: parent evaluations of being informed of their child's major abnormality

studied with specially developed catheter based high-resolution, real-time miniature ultrasound transducer. Each brain mantle and secondary brain vesicles could be clearly visualized, and thickness of telencephalon, diencephalon, mesencephalon and rhombencephalon were measured. The normal range of embryonic brain mantle measurements for each day of pregnancy was determined. A linear relationships were found between the gestational age and telencephalon thickness (R2 = 51.9%), diencephalon thickness (R2 = 62.2%), mesencephalon thickness (R2 = 59.2%), and rhombencephalon thickness (R2 = 47.8%), respectively. A linear relationships were also found between the crown-rump length and telencephalon thickness (R2 = 55.0%), diencephalon thickness (R2 = 58.3%), mesencephalon thickness (R2 = 55.0%), and rhombencephalon thickness (R2 = 52.3%), respectively. These results suggest that intrauterine sonography provide an accurate embryonic brain mantle measurement value in utero. Moreover, intrauterine sonography may become an important modality in future embryonal research and in detection of embryonic brain developmental disorders in the early first-trimester pregnancy.

Laparoscopy-Assisted Intrapelvic Sonography with a High-Frequency, Real-Time Miniature Transducer to Assess the Ovary: A Preliminary Report

Objective: Our purpose was to evaluate the normal and pathologic internal textures of the ovary using laparoscopy-assisted intrapelvic sonography (LAIPS) with a specially developed 20-MHz flexible catheter-based high-resolution real-time miniature (2.4 mm in outer diameter) ultrasound transducer in patients with gynecologic disorders and infertile women. Methods: 30 women (19 patients with gynecologic disorders and normal menstrual cycles (2 adenomyoses, 1 cervical cancer, 5 fibromyomas, 5 simple ovarian cysts, 1 endometriosis, 3 benign cystic teratomas, and 2 endometriomas), and 11 patients with infertility including 4 with polycystic ovarian syndrome, PCOS) were studied by intrapelvic sonography using a high-frequency real-time miniature transducer with pelvic saline effusion and laparoscopy. Results: In the normal ovary in the mid-follicular phase, follicles were depicted more distinctly than with transvaginal sonography (TVS). In the late-follicular phase, cumulus oophorus formations were visualized in 6 of 9 patients (54.5%), but were not clear using TVS. In the luteal phase, the corpus luteum was noted in 9 of 12 patients (75%) by both TVS and LAIPS. In patients with PCOS, the thickened capsule of the ovary was distinguished clearly especially in the peripheral type, in which numerous small cysts were aligned in the subcapsular region of the ovary, whereas it could not be detected by TVS. In all 4 cases with PCOS (8 ovaries), the ovarian capsular thickness could be measured by means of LAIPS. In subjects with benign cystic teratoma, minimal high echoic lesions were depicted. In subjects with endometrioma, a diffuse coarse-granular internal texture was visualized. However, depiction of internal structures in large pathologic ovarian lesions was markedly limited because of the shallow scanning range of the high-frequency transducer. Conclusion: LAIPS with a high-frequency real-time miniature transducer might be a useful diagnostic modality to evaluate the normal physiologic textures of the ovary, as well as those with PCOS.

High-frequency endoluminal ultrasonography for staging transitional cell carcinoma of the bladder

Objectives. To assess the feasibility and limitations of endoluminal ultrasound (ELUS) for clinical staging of bladder tumors. Methods. From 1998 to 1999, 32 patients with transitional cell carcinoma of the bladder were evaluated by high-frequency ELUS using miniature ultrasound transducers (20 MHz, 5.1F or 7.2F) before transurethral resection. Clinical staging using ELUS was compared with the results of pathologic staging. Results. Seventeen (94%) of the 18 patients with superficial tumors on ELUS were confirmed by pathologic examination to have Stage pTa (n = 12) or Stage pT1 (n = 5) disease, and 11 (63%) of the 14 patients with muscle-invasive tumors on ELUS were confirmed by pathologic evaluation to have Stage pT2a (n = 2) or Stage pT2b (n = 9) disease. In all of the misdiagnosed patients, the tumor lacked a well-defined base and was larger than 2 cm in size. It was difficult to distinguish between Stage Ta and Stage T1 tumors because of the limited resolution of ELUS and between Stage T2a and Stage T2b tumors because of its low penetration. Conclusions. ELUS using a high-frequency (20 MHz), miniature ultrasound transducer is able to distinguish superficial tumors from those with muscle invasion. However, the lack of penetration of the sonographic beam places major limitations on the evaluation of the depth of the invasion in large (greater than 2 cm) tumors with a broad base.

Intrauterine sonographic measurement of embryonic brain vesicle.

Our purpose was to evaluate embryonic brain vesicle measurements using intrauterine sonography in early first-trimester pregnancy. Fifty-one women about to undergo therapeutic abortion from 7-9.9 weeks gestational age were studied with a specially developed flexible catheter-based high-resolution real-time miniature (2.4 mm in outer diameter) ultrasound transducer (20 MHz). Length, width and height of telencephalon, diencephalon, mesencephalon and rhombencephalon were measured. The normal range of embryonic brain vesicle measurements for each day of pregnancy was determined. Curvilinear relationships were found between the menstrual age and telencephalon height (r(2) = 71.2%), diencephalon length (r(2) = 39. 6%), width (r(2) = 39.4%) and height (r(2) = 48.3%) and mesencephalon length (r(2) = 59.0%) respectively. Linear relationships were found between the menstrual age and telencephalon width (r(2) = 41.4%), mesencephalon height (r(2) = 58.7%) and rhombencephalon length (r(2) = 44.9%), width (r(2) = 56.8%) and height (r(2) = 35.5%) respectively. Telencephalon length and mesencephalon width were constant throughout menstrual age. These results suggest that intrauterine sonography provides accurate embryonic brain measurements in utero. Moreover, intrauterine sonography may become an important modality in future embryological research and in detection of embryonic brain developmental disorders in early first-trimester pregnancy.

Intrauterine Sonographic Visualization of Embryonic Genital Tubercle

Objective: To visualize embryonic genital tubercle using intrauterine sonography with a 20-MHz flexible catheter-based high-resolution real-time miniature transducer in early first-trimester pregnancy. Design: Randomized prospective study. Methods: A total of 39 women about to undergo therapeutic abortion from 7 to 10 weeks’ gestational age were studied with specially developed catheter-based high-resolution real-time miniature (2.4 mm in outer diameter) ultrasound transducer (20 MHz). Before the intrauterine sonographic procedure was performed, transvaginal sonographic assessment of the embryo was conducted. The percentage of embryonic genital tubercle (or phallus) visualized at each gestational age using intrauterine and transvaginal sonography is presented. Results: The genital tubercle could not be identified at 7 weeks of gestation with intrauterine sonography. The genital tubercle was visualized in 30% of embryos at 8 weeks’ gestation, and in 100% of embryos at 9 and 10 weeks. The genital tubercle was situated somewhat cranially to the sacral prominence at this gestational age. The genital tubercle could not be depicted with transvaginal sonography between 7 and 10 weeks of gestation. Conclusions: Intrauterine sonography provides a novel means for visualization of genital tubercle of the embryo. These results suggest that intrauterine sonography can become an important modality in future embryological research and in detection of embryonic developmental disorders in the early first-trimester pregnancy.

Laparoscopy-assisted intrapelvic sonography with a high-frequency, real-time miniature transducer for assessment of the Fallopian tube: a preliminary report.

Our purpose was to visualize normal and abnormal Fallopian tubes using laparoscopy-assisted intrapelvic sonography with a specially developed 20 MHz flexible catheter-based high-resolution, real-time miniature (2.4 mm outer diameter) ultrasound transducer in infertile women. A total of 21 women (20 infertile, one with unilateral hydrosalpinx, and one tubal pregnancy) were studied with pelvic saline effusion under laparoscopy. Fimbriae were clearly depicted with a cockscomb-like form in 95% of patients. All ampullae were visualized, and mucosal layers were clearly distinguished from muscle layers in 70% of patients. Scanty intratubal effusion was noted in 50% of patients, and tubal spastic findings were found in 10% of patients. In all, 60% of isthmuses were detected, and mucosal layers were distinguished from muscle layers in 30%. In the subject with hydrosalpinx, the tubal wall was thinner, and it was not possible to distinguish between muscle and mucosal layers. In the subject with a tubal pregnancy, the amniotic membrane and decidua were depicted more clearly than by transvaginal sonography. In conclusion, laparoscopy-assisted intrapelvic sonography with a high-frequency, real-time miniature transducer may be useful in the assessment of tubal texture and function in tubal disorders, possibly in infertility practice.

Three-dimensional intrauterine sonography in the early first-trimester of human pregnancy: preliminary study.

Our purpose was to visualize normal embryonal surface anatomic structures using three-dimensional (3D) intrauterine sonography with a 20 MHz flexible catheter-based high-resolution real-time miniature transducer in the early first trimester of pregnancy. A total of 15 women about to undergo therapeutic abortion at 7-9.9 weeks gestational age were studied by means of 3D intrauterine sonography with a specially developed catheter-based high-resolution real-time miniature (2.4 mm in outer diameter) ultrasound transducer (20 MHz). This imaging system can provide conventional 2D intrauterine sonographic images and can also generate within seconds high-quality 3D images in the surface and transparent mode. At week 8, prominent forehead was evident, and upper and lower limbs and midgut herniation were clearly depicted. At week 9, fingers and toes were depicted as small digital rays, and the sacral tail protruded caudally. The midline cranial ectodermal cleft was also identified. At week 10, embryonic face and fingers were clearly shown. 3D intrauterine sonography provides a novel means for visualizing of surface anatomic structures of the human embryo in utero. These results suggest that 3D intrauterine sonography can become an important modality in future embryological research and in detection of embryonic developmental disorders in the early first-trimester pregnancy.

Intrauterine sonographic assessments of embryonic heart diameter.

Our purpose was to evaluate embryonic heart diameter in early first-trimester pregnancy using intrauterine sonography with a 20 MHz flexible catheter-based high-resolution real-time miniature transducer. A total of 40 women about to undergo therapeutic abortion from 6-9.9 weeks gestational age and one abnormal pregnancy with fetal hydrops at 9 weeks were studied with a specially developed catheter-based high-resolution real-time miniature (2.4 mm outer diameter) ultrasound transducer (20 MHz). A curvilinear relationship was found between the menstrual age and embryonic heart diameter (R2 = 95.7%), and a normal range of embryonic heart diameter for estimating the growth of the embryonic heart during early first-trimester pregnancy was generated. A normogram of menstrual age as predicted by embryonic heart diameter was also established. There was a good curvilinear correlation between embryonic heart diameter and crown-rump length (R2 = 90.1%). The embryonic heart diameter/crown-rump length ratio rapidly decreased from week 6 to week 7, and remained almost constant thereafter. Embryonic heart diameter (5.2 mm) in the case of fetal hydrops at 9 weeks was above the normal range. These results may provide an additional method of estimating gestational age in the early first trimester of pregnancy. In this limited series, a single case of embryonic heart enlargement was demonstrated, suggesting its potential use in the detection of embryonic congestive heart failure.