Testing telediagnostic thyroid ultrasound in Peru: a new horizon in expanding access to imaging in rural and underserved areas.

PURPOSE: Thyroid ultrasound is a key tool in the evaluation of the thyroid, but billions of people around the world lack access to ultrasound imaging. In this study, we tested an asynchronous telediagnostic ultrasound system operated by individuals without prior ultrasound training which may be used to effectively evaluate the thyroid and improve access to imaging worldwide. METHODS: The telediagnostic system in this study utilizes volume sweep imaging (VSI), an imaging technique in which the operator scans the target region with simple sweeps of the ultrasound probe based on external body landmarks. Sweeps are recorded and saved as video clips for later interpretation by an expert. Two operators without prior ultrasound experience underwent 8 h of training on the thyroid VSI protocol and the operation of the telemedicine platform. After training, the operators scanned patients at a health center in Lima. Telediagnostic examinations were sent to the United States for remote interpretation. Standard of care thyroid ultrasound was performed by an experienced radiologist at the time of VSI examination to serve as a reference standard. RESULTS: Novice operators scanned 121 subjects with the thyroid VSI protocol. Of these exams, 88% were rated of excellent image quality showing complete or near complete thyroid visualization. There was 98.3% agreement on thyroid nodule presence between VSI teleultrasound and standard of care ultrasound (Cohen's kappa 0.91, P < 0.0001). VSI measured the thyroid size, on average, within 5 mm compared to standard of care. Readers of VSI were also able to effectively characterize thyroid nodules, and there was no significant difference in measurement of thyroid nodule size (P = 0.74) between VSI and standard of care. CONCLUSION: Thyroid VSI telediagnostic ultrasound demonstrated both excellent visualization of the thyroid gland and agreement with standard of care thyroid ultrasound for nodules and thyroid size evaluation. This system could be deployed for evaluation of palpable thyroid abnormalities, nodule follow-up, and epidemiological studies to promote global health and improve the availability of diagnostic imaging in underserved communities.

Biomechanical response to acupuncture needling in humans.

During acupuncture treatments, acupuncture needles are manipulated to elicit the characteristic "de qi" reaction widely viewed as essential to acupuncture's therapeutic effect. De qi has a biomechanical component, "needle grasp," which we have quantified by measuring the force necessary to pull an acupuncture needle out of the skin (pullout force) in 60 human subjects. We hypothesized that pullout force is greater with both bidirectional needle rotation (BI) and unidirectional rotation (UNI) than no rotation (NO). Acupuncture needles were inserted, manipulated, and pulled out by using a computer-controlled acupuncture needling instrument at eight acupuncture points and eight control points. We found 167 and 52% increases in mean pullout force with UNI and BI, respectively, compared with NO (repeated-measures ANOVA, P < 0.001). Pullout force was on average 18% greater at acupuncture points than at control points (P < 0.001). Needle grasp is therefore a measurable biomechanical phenomenon associated with acupuncture needle manipulation.

Interlaboratory comparison of ultrasonic backscatter, attenuation, and speed measurements.

In a study involving 10 different sites, independent results of measurements of ultrasonic properties on equivalent tissue-mimicking samples are reported and compared. The properties measured were propagation speed, attenuation coefficients, and backscatter coefficients. Reasonably good agreement exists for attenuation coefficients, but less satisfactory results were found for propagation speeds. As anticipated, agreement was not impressive in the case of backscatter coefficients. Results for four sites agreed rather well in both absolute values and frequency dependence, and results from other sites were lower by as much as an order of magnitude. The study is valuable for laboratories doing quantitative studies.

Elastography: ultrasonic estimation and imaging of the elastic properties of tissues.

The basic principles of using sonographic techniques for imaging the elastic properties of tissues are described, with particular emphasis on elastography. After some preliminaries that describe some basic tissue stiffness measurements and some contrast transfer limitations of strain images are presented, four types of elastograms are described, which include axial strain, lateral strain, modulus and Poisson's ratio elastograms. The strain filter formalism and its utility in understanding the noise performance of the elastographic process is then given, as well as its use for various image improvements. After discussing some main classes of elastographic artefacts, the paper concludes with recent results of tissue elastography in vitro and in vivo.

Viewing DICOM-compliant CT images on a desktop personal computer: use of an inexpensive DICOM receive agent and freeware image display applications.

OBJECTIVE: Our objective was to determine the ease of installation and use of relatively inexpensive and free software applications that allow Macintosh users to receive and view CT images from a Digital Imaging and COmmunication in Medicine-compliant imaging network. CONCLUSION: Simple-to-use Macintosh-based options to transfer and view images are readily available and easily installed by users with minimal computer expertise.

Assessment of bone density using ultrasonic backscatter.

The goal of this project was to investigate the utility of ultrasonic backscatter for the assessment of bone status. Ultrasound offers a low-cost, portable, nonionizing alternative or complement to common X-ray- or radioisotope (gamma ray)-based methods of bone densitometry. Ultrasonic backscatter may provide useful information not revealed by ultrasonic attenuation and sound-speed densitometers. Backscatter is sensitive to microstructural variations in acoustic impedance and should therefore provide information regarding architecture (which is related to fracture risk), as well as density. Ultrasonic backscatter at 2.25 MHz and CT bone densitometric data have been acquired from 10 healthy human volunteers. The degree of correlation between CT and ultrasonic backscatter is high (r = 0.87, p < 0.001). The envelope signal-to-noise ratio was 1.81 +/- 0.08 (mean +/- standard deviation). This suggests that the number of scatterers per resolution cell is large, the radiofrequency signal approximately obeys circular Gaussian statistics, and the envelope obeys Rayleigh statistics. These results indicate promise for ultrasonic backscatter as a substitute for or an adjunct to other ultrasonic measurements (attenuation and sound speed) and X-ray measurements for the assessment of bone status.

Elastic moduli of breast and prostate tissues under compression.

To evaluate the dynamic range of tissue imaged by elastography, the mechanical behavior of breast and prostate tissue samples subject to compression loading has been investigated. A model for the loading was validated and used to guide the experimental design for data collection. The model allowed the use of small samples that could be considered homogeneous; this assumption was confirmed by histological analysis. The samples were tested at three strain rates to evaluate the viscoelastic nature of the material and determine the validity of modeling the tissue as an elastic material for the strain rates of interest. For loading frequencies above 1 Hz, the storage modulus accounted for over 93 percent of the complex modulus. The data show that breast fat tissue has a constant modulus over the strain range tested while the other tissues have a modulus that is dependent on the strain level. The fibrous tissue samples from the breast were found to be 1 to 2 orders of magnitude stiffer than fat tissue. Normal glandular breast tissue was found to have an elastic modulus similar to that of fat at low strain levels, but the modulus of the glandular tissue increased by an order of magnitude above fat at high strain levels. Carcinomas from the breast were stiffer than the other tissues at the higher strain level; intraductal in situ carcinomas were like fat at the low strain level and much stiffer than glandular tissue at the high strain level. Infiltrating ductal carcinomas were much stiffer than any of the other breast tissues. Normal prostate tissue has a modulus that is lower than the modulus of the prostate cancers tested. Tissue from prostate with benign prostatic hyperplasia (BPH) had modulus values significantly lower than normal tissue. There was a constant but not significant difference in the modulus of tissues taken from the anterior and posterior portions of the gland.

Elastography of breast lesions: initial clinical results.

PURPOSE: To determine the appearance of various breast lesions on elastograms and to explore the potential of elastography in the diagnosis of breast lesions. MATERIALS AND METHODS: A total of 46 breast lesions were examined with elastography. Patients underwent biopsy or aspiration of all lesions, revealing 15 fibroadenomas, 12 carcinomas, six fibrocystic nodules, and 13 other lesions. The elastogram was generated from radio-frequency data collected with use of a 5-MHz linear-array transducer. The elastogram and corresponding sonogram were evaluated by a single observer for lesion visualization, relative brightness, and margin definition and regularity. The sizes of the lesions at each imaging examination and at biopsy were recorded and compared. RESULTS: Softer tissues such as fat appear as bright areas on elastograms. Firm tissues, including parenchyma, cancers, and other masses, appear darker. The cancers were statistically significantly darker than fibroadenomas (P < .005) and substantially larger on the elastogram than on the sonogram. Seventy-three percent of fibroadenomas and 56% of solid benign lesions could be distinguished from cancers by using lesion brightness and size difference. Some cancers that appeared as areas of shadowing on sonograms appeared as discrete masses on elastograms. CONCLUSION: Elastography has the potential to be useful in the evaluation of areas of shadowing on the sonogram. It also may be helpful in the distinction of benign from malignant masses.

Helical CT of renal masses: the value of delayed scans.

OBJECTIVE: Routine scanning techniques used for helical CT of the abdomen result in dense cortical opacification of the kidney, whereas the medulla and collecting system are not well opacified, which potentially compromises detection of renal masses. The purpose of this retrospective study was to determine if additional delayed views (taken approximately 2-4 min after the start of injection of contrast material) are necessary for the detection and characterization of renal masses. MATERIALS AND METHODS: Early (60-70 sec after the start of the injection of contrast material) and delayed scans of 40 patients with suspected renal masses were blindly evaluated by two observers. The patients harbored a total of 187 renal masses (including 62 solid masses). Each region of the kidney (upper, middle, and lower pole) was scored for the presence of a mass. Scoring was done as a binary decision and also as a five-point confidence score for receiver operating characteristic analysis. RESULTS: We found 97 regions that contained renal masses and 114 regions that did not. Receiver operating characteristic analysis revealed the observers to have significantly greater confidence in detection of renal masses on the delayed scans. The binary data showed the two observers to have a sensitivity of 97% for delayed scans versus 77% (p = .0002) and 89% (p = .027), respectively, for the early scans. For the first observer, early and delayed scans were of equal specificity, but for the second observer, the delayed scans yielded greater specificity (94% versus 85%, p = .024). On the early scans, both observers were significantly more likely to miss a neoplastic lesion than a nonneoplastic lesion. The less experienced of the two observers also tended to have greater difficulty in characterizing the lesions on the early scans. CONCLUSION: Because of the significant risk of missing a renal mass, especially a neoplasm, on early cortical-phase scans, additional delayed scans appear justified when a renal mass is suspected on the basis of other imaging tests or clinical history.

Scrotal-inguinal ultrasonography: a technique for identifying the nonpalpable inguinal testis without laparoscopy.

PURPOSE: Treatment of the patient with a nonpalpable testis is controversial, since a high percent will have an inguinal testis or testicular remnant at exploration. While laparoscopy is an effective modality for localizing the intra-abdominal testis, diagnostic laparoscopy is of limited value for patients with nonpalpable (normal or atrophic) inguinal testes. In an effort to identify preoperatively impalpable inguinal testes, we performed scrotal-inguinal ultrasound. MATERIALS AND METHODS: We evaluated 64 patients (74 nonpalpable testes) in the last 4 years, representing 20% of all those presenting with cryptorchidism. Average patient age was 4.5 years (range 6 months to 17 years). All patients underwent preoperative scrotal-inguinal ultrasound and surgical exploration. Diagnostic laparoscopy was reserved for patients with negative ultrasound and no palpable tissue in the scrotum or groin on a preoperative examination. RESULTS: Scrotal-inguinal ultrasound correctly identified 40 of the 42 inguinal testes (95% sensitivity), 7 of the 21 atrophic inguinal testes (33% sensitivity) and 1 of the 11 intra-abdominal testes (9% sensitivity). Therefore, scrotal-inguinal ultrasound correctly identified an inguinal testis or remnant for 47 of the 74 nonpalpable testes (64%), eliminating the need for diagnostic laparoscopy in those cases. For 26 of 74 nonpalpable testes with negative ultrasound 13 had an associated palpable inguinal or scrotal nubbin of tissue, and inguinal exploration only was performed, resulting in 9 orchiectomies, 2 inguinal orchiopexies and 2, 2-stage orchiopexies. Of the 13 nonpalpable testes without palpable nubbins and negative scrotal-inguinal ultrasound 8 were intra-abdominal and 5 were atrophic inguinal testes. CONCLUSIONS: Scrotal-inguinal ultrasound identifies patients with nonpalpable testes who will maximally benefit from diagnostic laparoscopy. When diagnostic laparoscopy was limited to nonpalpable testes without palpable nubbins and negative scrotal-inguinal ultrasound, only 13 of 74 (18%) required laparoscopy. Inguinal exploration without further diagnostic studies is appropriate for boys with nonpalpable testes and palpable nubbins.

Quantitative sonographic feature analysis of clinical infant hypoxia: a pilot study.

PURPOSE: To determine whether textural features derived from sonographic pixel intensities differ significantly between healthy infants and infants who have had acute clinical hypoxic episodes. METHODS: Neurosonographic and calibration phantom-processed image data were evaluated prospectively from 9 infants (age range, 1 to 163 days) with at least 1 episode of hypoxia and compared with image data from a control population of 16 healthy infants (age range, 1 to 191 days). Custom software was used to make 45 textural feature measurements on 40 x 40-pixel regions of interest within brain parenchyma in the distribution of each major cerebral artery, the thalami, and the cerebellum and in a tissue-mimicking calibration phantom. Means comparison testing was followed by logistic regression to assess statistical variation between the patients and the control group. RESULTS: Nine of 45 textural features showed statistically significant differences between mean values comparing the two groups. Mean gray level was the most sensitive predictor of differences between the two populations (mean gray level for healthy subjects was 46.8; mean gray level for patients was 56.3). An average of mean gray values in areas supplied by the posterior cerebral arteries and the cerebellum was even more sensitive for differentiating healthy subjects from patients. CONCLUSIONS: Quantitative sonographic textural feature analysis showed differences between the brains of healthy infants and those of infants with clinical hypoxia.

Measurements of ultrasonic backscatter coefficients in human liver and kidney in vivo.

Ultrasonic backscatter coefficients, in the range of 2.0-4.0 MHz, were measured in normal human livers and kidneys in vivo. In liver, data were acquired and analyzed from 15 normal volunteers and 19 patients with hepatitis. No significant difference between normal and chronic hepatitis was found. The power-law fit to the backscatter coefficient in normal liver as a function of frequency was eta(f) = 4.5 x 10(-5) f1.6 cm-1 Str-1. This is comparable to that measured by other investigators in in vitro preparations of human and animal liver and to that measured by two other teams of investigators in in vivo human liver. In kidney, data were acquired from 11 normal volunteers. The power-law fit to the backscatter coefficient in normal kidney was eta (f) = 2.3 x 10(-5) f2.1 cm-1 Str-1. This is in the range of that measured by other investigators in in vitro preparations of human and animal kidney. In order to assess the system dependence of in vivo abdominal organ backscatter coefficients, measurements were performed using two different ultrasonic data-acquisition systems. The two systems exhibited close agreement.

Biliary tract: three-dimensional helical CT without cholangiographic contrast material.

Bile duct anatomy depicted with a three-dimensional (3D) model developed with helical computed tomography (CT) data was compared with cholangiographic depiction. The ductal system was completely displayed from all angles in four of six patients, as well as the stricture and length of bile duct between strictures and the bifurcation in five of six cases. 3D rendering can depict preoperative ductal anatomy.

The optimal temporal window for CT of the liver using a time-density analysis: implications for helical (spiral) CT.

OBJECTIVE: Scanning protocols for conventional CT of the liver have been proposed. Current availability of helical CT with a four- to sixfold decrease in scan time requires significant adjustments in these protocols. The present study assesses the implications of time-density curves on the performance of helical liver CT. MATERIALS AND METHODS: Twenty patients without liver lesions were studied for time-density analysis of the aorta, inferior vena cava (ICV), portal vein, and liver. Scans were performed at the level of the portal vein at baseline and every 15 s for 3 min following uniphasic administration of 150 ml (300 mg I/ml) nonionic contrast agent. Regions of interest were used to measure three areas in each anatomic structure over time. Median and mean peak enhancement times were calculated for all 20 patients. Cubic spline interpretation was employed to determine the point of equilibrium. RESULTS: Results demonstrated the following average maximum enhancement values and times for peak enhancement: aorta: 227 HU (75 s); liver: 123 HU (105 s); portal vein: 187 HU (90 s); IVC: 142 HU (90 s). Hepatic enhancement achieved 67 HU over baseline. Peak portal enhancement occurred 15 s prior to liver enhancement (p = 0.001). Aortic and hepatic curves became parallel (onset of equilibrium) at a median time of 120 s. CONCLUSION: Helical scanning requires a longer delay (70-80 s) than used for conventional CT. Upon application of these principles, scan initiation occurs higher on the liver enhancement curve, improving liver enhancement without impinging on equilibrium.

US tissue characterization workstation: applications and design.

This article discusses the purpose, design, and uses of an ultrasonographic tissue characterization workstation. The distinguishing characteristic of a tissue characterization workstation is its ability to analyze and classify image textures. Texture is defined as regularly or randomly repeating patterns. Small texture differences in an image are difficult to observe in the presence of noise. Therefore, it is necessary to analyze the image quantitatively. Quantitative measurements include run-length statistics, fractal dimension, and correlation statistics. The workstation is designed so that a radiologist can analyze the patient's images through an easy-to-use graphical user interface. The workstation software is based on standards, so that it can be run on a variety of different hardware platforms. The workstation can be used in a research environment to distinguish between images of malignant and benign breast lesions, which are difficult to diagnose visually. Further work is being done to make the workstation software into a useful clinical tool.

Understanding the process of quantitative ultrasonic tissue characterization.

Because the human vision system cannot distinguish the broad range of gray values that a computer visual system can, computerized image analysis may be used to obtain quantitative information from ultrasonographic (US) real-time B-mode scans. Most quantitative US involves programming an off-line computer to accept, analyze, and display US image data in a way that enhances the detection of changes in small-scale structures and blood flow that occur with disease. Common image textural features used in quantitative US tissue characterization consist of first-order gray-level statistics (eg, occurrence frequency of gray levels independent of location or spatial relationship) and second-order gray-level statistics dependent on location and spatial relationship, including statistical analysis of gradient distribution, co-occurrence matrix, covariance matrix, run-length histogram, and fractal features. A customized tissue signature software has been developed to analyze image data obtained from clinical US scanners. Means comparison testing and multivariate analysis techniques are used to compare the numbers generated for a particular region of interest. By integrating these techniques into the radiologist's interpretation of the sonogram, the quantitative information gained may lead to earlier detection of lesions difficult to see with the human eye.

Quantitative ultrasonic detection of parenchymal structural change in diffuse renal disease.

OBJECTIVE: The authors determined whether quantitative ultrasound could be useful in the evaluation of diffuse renal disease. METHODS: Digitized radiofrequency ultrasound data were acquired from the kidneys of patients with biopsy-proven diffuse renal disease and transplant rejection (37 patients plus 18 normal volunteers). The results of the quantitative analysis were compared with histology results to determine if microscopic renal structure could be correlated with quantitative features such as scatterer size and scatterer spacing. The results also were analyzed using receiver operating characteristic analysis to determine if diffuse disease could be detected reliably using quantitative methods. RESULTS: The three most useful features in the native kidneys were mean scatterer spacing (MSS), sigma's, and average scatterer size (D). Using these features, it was possible to detect diffuse renal disease causing a decrease in renal function with an area under the ROC curve (Az) of 0.93. The feature D corresponded closely to histologically measured average glomerular diameters. For normals, D = 216 microns and glomerular diameter = 211 microns. No histologic correlate was found for scatterer spacing. In transplants, MSS and integrated backscatter were most useful for detecting rejection (Az = 0.87), and D in rejection was similar to the values for normal kidney and normally functioning transplants. CONCLUSIONS: The D value corresponds to glomerular diameter, and glomerular enlargement can be detected readily using quantitative ultrasound. Combinations of two to four quantitative features can detect diffuse renal disease and transplant rejection reliably.

Image staining and differential diagnosis of ultrasound scans based on the Mahalanobis distance.

The covariance matrices associated with each state of health or disease from a previous study are used as the basis of an image staining display technique for aid in quantitative differential diagnosis. A state of health or disease is chosen by the clinician: this selects the covariance matrix from the data base. A region of interest (ROI) is then scrolled through an abdominal B-scan. For each position of the ROI a point in the four-dimensional feature space is calculated. A natural measure of the distance of this point from the center of mass (multivariate mean) of the disease class is calculated in terms of the covariance matrix of this class; this measure is the Mahalanobis distance. The confidence level for acceptance or rejection of the hypothesized disease class is obtained from the probability distribution of this distance, the T(2) probability law. This confidence level is color coded and used as a color stain that overlays the original scan at that position. The variability of the calculated features is studied as a function of ROI size, or the spatial resolution of the color coded image, and it is found that for an ROI in the neighborhood of 4 cm(2) most of the variability due to the finite number of independent samples (speckles) is averaged out, leaving the "noise floor" associated with inter- and intra-patient variability. ROIs on the order of 1 cm(2) may result with technical advances in B-scan resolution. A small number of points on organ boundaries are entered by the user, to fit with arcs of ellipses to be used to switch between organ (liver and kidney) data bases as the ROI encounters the boundary. By selecting in turn various state-of-health or state-of-disease databases, such images of confidence levels may be used for quantitative differential diagnosis. The method is not limited to ultrasound, being applicable in principle to features obtained from any modality or multimodality combination.