Comparison of the 18F-FDG avidity at PET of benign and malignant pure ground-glass opacities: a paradox?

AIM: To determine if pure ground-glass opacities (GGOs) and the subgroup of ground-glass nodules (GGNs) typically demonstrate higher 2-[18F]-fluoro-2-deoxy-d-glucose (18F-FDG) uptake at positron-emission tomography (PET) when benign than when malignant. MATERIALS AND METHODS: Informed consent was waived for this institutional review board (IRB)-approved, Health Insurance Portability and Accountability Act (HIPAA) compliant, retrospective study. A review of all 1,864 combined PET/computed tomography (CT) examinations performed in 2011 on a single system to identify pure GGOs with mean diameter ≥1 cm yielded 166 GGOs. Two blinded subspecialty-trained thoracic radiologists independently assessed GGO size, morphology, attenuation, and location on CT. A blinded nuclear radiologist procured the SUVmax for each GGO. Final diagnosis of malignancy (n=21) was made based on histopathology or upon increased size and attenuation; a final diagnosis of benignity (n=106) was made if GGO resolved, was new within 3 months, evolved in a manner consistent with pulmonary fibrosis, or was stable for ≥60 months; 29 were indeterminate and were excluded, along with 10 cases with unreliable SUVmax measurements, yielding 127 GGOs, of which 68 were GGNs, in 76 patients. RESULTS: The SUVmax was significantly higher in benign than malignant GGOs (p=0.0017) and in the GGN subgroup (p=0.03). A threshold SUVmax >1.5 for GGOs, including GGNs, assured benignity in this cohort. CONCLUSION: Benign GGOs and the benign GGN subgroup demonstrated significantly higher FDG uptake at PET than malignant GGOs/GGNs. Awareness of this finding may prevent misinterpretation of highly 18FDG-avid pure GGOs/GGNs as definitively malignant, which could lead to unnecessary thoracic surgery and its associated risks.

Comparison of 18F-FDG avidity at PET of benign and malignant pure ground-glass opacities: a paradox? Part II: artificial neural network integration of the PET/CT characteristics of ground-glass opacities to predict their likelihood of malignancy.

AIM: To assess the ability of artificial neural networks (ANNs) to predict the likelihood of malignancy of pure ground-glass opacities (GGOs), using observations from computed tomography (CT) and 2-[18F]-fluoro-2-deoxy-d-glucose (FDG) positron-emission tomography (PET) images and relevant clinical information. MATERIALS AND METHODS: One hundred and twenty-five cases of pure GGOs described in a previous article were used to train and evaluate the performance of an ANN to predict the likelihood of malignancy in each of the GGOs. Eighty-five cases selected randomly were used for training the network and the remaining 40 cases for testing. The ANN was constructed from the image data and basic clinical information. The predictions of the ANN were compared with blinded expert estimates of the likelihood of malignancy. RESULTS: The ANN showed excellent predictive value in estimating the likelihood of malignancy (AUC = 0.98±0.02). Employing the optimal cut-off point from the receiver operating characteristic (ROC) curve, the ANN correctly identified 11/11 malignant lesions (sensitivity 100%) and 27/29 benign lesions (specificity 93.1%). The expert readers found 23 lesions indeterminate and correctly identified 17 lesions as benign. CONCLUSION: ANNs have potential to improve diagnostic certainty in the classification of pure GGOs, based upon their CT appearance, intensity of FDG uptake, and relevant clinical information, and may therefore, be useful to help direct clinical and imaging follow-up.

Acute Gouty Knee Arthritis: Ultrasound Findings Compared With Dual-Energy CT Findings.

OBJECTIVE: The purpose of this study was to compare findings of ultrasound (US) with dual-energy CT (DECT) findings in patients presenting with suspected gouty knee arthritis. SUBJECTS AND METHODS: This prospective study included 65 patients (52 men and 13 women; median age, 61.7 years [range, 38-87 years]) with an initial clinical diagnosis of acute gouty knee arthritis who underwent DECT performed using a 128-MDCT scanner and US performed using a 5-18-MHz transducer. Both intra- and extraarticular findings obtained using each modality were tabulated. RESULTS: DECT identified gout as the final diagnosis for 52 of 65 patients (80.0%). An alternative diagnosis was confirmed for the remaining 13 patients. US detected gout in 31 of 52 patients (sensitivity, 59.6%) and produced findings negative for gout in seven of 13 patients (specificity, 53.8%). The double contour sign on US was positive for gout in 23 of 52 patients (44.2%) and negative in 12 of 13 patients (92.3%). Extraarticular urate deposition was identified by DECT in 44 of 52 patients, compared with identification by US in 11 of 52 patients (p < 0.001). CONCLUSION: The sensitivity of US for the diagnosis of gouty knee arthritis is limited, particularly with respect to extraarticular urate deposition. The double contour sign is the single most valuable sign for the assessment of gouty knee arthritis by US.

Reconstruction of surface potential from Kelvin probe force microscopy images.

We present an algorithm for reconstructing a sample surface potential from its Kelvin probe force microscopy (KPFM) image. The measured KPFM image is a weighted average of the surface potential underneath the tip apex due to the long-range electrostatic forces. We model the KPFM measurement by a linear shift-invariant system where the impulse response is the point spread function (PSF). By calculating the PSF of the KPFM probe (tip+cantilever) and using the measured noise statistics, we deconvolve the measured KPFM image to obtain the surface potential of the sample.The reconstruction algorithm is applied to measurements of CdS-PbS nanorods measured in amplitude modulation KPFM (AM-KPFM) and to graphene layers measured in frequency modulation KPFM (FM-KPFM). We show that in the AM-KPFM measurements the averaging effect is substantial, whereas in the FM-KPFM measurements the averaging effect is negligible.

Clinical, Imaging, and Lab Correlates of Severe COVID-19 Leukoencephalopathy.

BACKGROUND AND PURPOSE: Patients infected with the Severe Acute Respiratory Syndrome coronavirus 2 (SARS-CoV-2) can develop a spectrum of neurological disorders, including a leukoencephalopathy of variable severity. Our aim was to characterize imaging, lab, and clinical correlates of severe coronavirus disease 2019 (COVID-19) leukoencephalopathy, which may provide insight into the SARS-CoV-2 pathophysiology. MATERIALS AND METHODS: Twenty-seven consecutive patients positive for SARS-CoV-2 who had brain MR imaging following intensive care unit admission were included. Seven (7/27, 26%) developed an unusual pattern of "leukoencephalopathy with reduced diffusivity" on diffusion-weighted MR imaging. The remaining patients did not exhibit this pattern. Clinical and laboratory indices, as well as neuroimaging findings, were compared between groups. RESULTS: The reduced-diffusivity group had a significantly higher body mass index (36 versus 28 kg/m2, P < .01). Patients with reduced diffusivity trended toward more frequent acute renal failure (7/7, 100% versus 9/20, 45%; P = .06) and lower estimated glomerular filtration rate values (49 versus 85 mL/min; P = .06) at the time of MRI. Patients with reduced diffusivity also showed lesser mean values of the lowest hemoglobin levels (8.1 versus 10.2 g/dL, P < .05) and higher serum sodium levels (147 versus 139 mmol/L, P = .04) within 24 hours before MR imaging. The reduced-diffusivity group showed a striking and highly reproducible distribution of confluent, predominantly symmetric, supratentorial, and middle cerebellar peduncular white matter lesions (P < .001). CONCLUSIONS: Our findings highlight notable correlations between severe COVID-19 leukoencephalopathy with reduced diffusivity and obesity, acute renal failure, mild hypernatremia, anemia, and an unusual brain MR imaging white matter lesion distribution pattern. Together, these observations may shed light on possible SARS-CoV-2 pathophysiologic mechanisms associated with leukoencephalopathy, including borderzone ischemic changes, electrolyte transport disturbances, and silent hypoxia in the setting of the known cytokine storm syndrome that accompanies severe COVID-19.

Transrectal Subharmonic Ultrasound Imaging for Prostate Cancer Detection.

OBJECTIVE: To assess the prostate cancer (CaP) detection rates of contrast-enhanced, transrectal subharmonic ultrasound imaging (SHI). MATERIALS AND METHODS: This IRB-approved study enrolled 55 subjects. The initial 5 subjects were studied for SHI optimization, while the remaining 50 were evaluated with contrast-enhanced sonography using continuous SHI, color, and power Doppler as well as conventional grayscale, continuous color, and power Doppler and SHI combined with maximum flash replenishment. A maximum of 6 directed biopsy cores were obtained from sites of greatest asymmetrical enhancement, followed by spatially distributed cores in a double sextant distribution. Subharmonic time-intensity parameters, including time to peak intensity, peak intensity, and estimated perfusion were also evaluated for each directed biopsy core. Receiver operating characteristic curve analysis and conditional logistic regression were employed to assess the benefit of each modality and the quantitative SHI parameters. RESULTS: Cancer was detected in 22 of 50 subjects. Among subjects with clinically significant CaP (n = 11), targeted cores were more likely to be positive (odds ratio 1.39, P = .02). The majority of patients detected by SHI demonstrated significant CaP (5/8); SHI remained an independent marker of malignancy in a multivariate logistic regression model (P = .027). Receiver operating characteristic curve analysis of imaging findings compared to biopsy results yielded diagnostic accuracies ranging from 0.59 to 0.80 for all imaging modalities with the highest being for quantitative subharmonic perfusion estimates. CONCLUSION: This first-in-humans study provides a preliminary estimate of the diagnostic accuracy of SHI for detection of clinically significant CaP (up to 80%).

Improved detection of metastatic melanoma by T2*-weighted imaging.

BACKGROUND AND PURPOSE: The imaging features of metastatic melanomas are distinctive due to the presence of melanin and the propensity for hemorrhage. Both hemorrhage and melanin can produce T1-weighted hyperintensity and T2*-weighted signal intensity loss. We hypothesized that T2*-weighted images would improve detection of metastatic melanoma. METHODS: The T2* and T1 characteristics of 120 newly detected metastatic brain lesions from 31 patients with malignant melanoma were compared with those of 120 brain metastases from 23 patients with lung cancer. RESULTS: Melanoma metastases were 5 times more likely to demonstrate prominent T2*-related signal intensity loss (susceptibility effect) than were lung metastases (42% vs 8%; P < .01), and 4.5 times more likely to demonstrate T1 hyperintensity (55% vs 12%; P < .01). Patients with melanoma had lesions that were either hypointense on T2*-weighted images, hyperintense on T1 images, or both, in 71% (85/120), compared with 19% (23/120) of lung carcinoma metastases (P < .01). Melanoma lesions were 16 times more likely than lung cancer lesions to show combined T2* related signal intensity loss and T1 hyperintensity (P < .01). Remarkably, 8 melanoma lesions (7%) in 3 patients were detectable principally on the T2*-weighted sequences, whereas no lung cancer lesion was detected solely on susceptibility images. We found a direct correlation between melanin content and T1 hyperintensity but no correlation between T2* intensity and melanin. CONCLUSION: T2*-weighted images improve lesion detection in patients with melanoma metastases, and in conjunction with T1-weighted sequences, can suggest melanoma as the etiology of an intracranial mass. This sequence should be employed for evaluation of possible brain metastasis in patients without a known primary malignancy and in studies for melanoma staging.

Poly(ethylene glycol)-coated anti-cardiac myosin immunoliposomes: factors influencing targeted accumulation in the infarcted myocardium.

Biodistribution and infarct accumulation of different liposome preparations in rabbits with experimental myocardial infarction have been investigated. The influence of such parameters as liposome size, and presence or absence of poly(ethylene glycol) (PEG) and infarct-specific antimyosin antibody (AM) on liposome behavior in vivo was studied. All three variables were shown to affect liposome biodistribution, liposome size being the least significant variable. Statistical analysis of the data obtained demonstrated that of all variables, PEG coating expresses the strongest influence on the liposome blood clearance, significantly (P=0.0001) increasing the mean level of blood radioactivity under all circumstances. Infarct accumulation depended upon the presence of both PEG (P=0.0013) and AM (P=0.005). The infarct-to-normal ratio was affected by the presence of AM (P=0.0002), but the extent of the effect depended also on the presence of PEG (P=0.01). Two differing mechanisms can be seen in infarct accumulation of PEG-liposomes (slow accumulation via the impaired filtration) and AM-liposomes (specific binding of immunoliposomes with the exposed antigen). Both mechanisms are supplementary in case of liposomes carrying PEG and AM at the same time. An optimization strategy is suggested for using liposomes as carriers for diagnostic (a high target-to-nontarget ratio is required) and therapeutic (a high absolute accumulation in the target is required) agents.

Schizophrenic subjects show aberrant fMRI activation of dorsolateral prefrontal cortex and basal ganglia during working memory performance.

BACKGROUND: Working memory (WM) deficits in schizophrenia have been associated with dorsolateral prefrontal cortex (DLPFC) dysfunction in neuroimaging studies. We previously found increased DLPFC activation in schizophrenic versus normal subjects during WM performance (Manoach et al 1999b). We now have investigated whether schizophrenic subjects recruit different brain regions, particularly the basal ganglia and thalamus, components of frontostriatal circuitry thought to mediate WM. METHODS: We examined regional brain activation in nine normal and nine schizophrenic subjects during WM performance using functional magnetic resonance imaging. Subjects performed a modified version of the Sternberg Item Recognition Paradigm that included a monetary reward for correct responses. We compared high and low WM load conditions to each other and to a non-WM baseline condition. We examined activation in both individual subjects and averaged group data. RESULTS: Relative to normal subjects, schizophrenic subjects exhibited deficient WM performance, at least an equal magnitude of right DLPFC activation, significantly greater left DLPFC activation, and increased spatial heterogeneity of DLPFC activation. Furthermore, only the schizophrenic group activated the basal ganglia and thalamus, even when matched for task performance with the normal group. CONCLUSIONS: Aberrant WM performance and brain activation in schizophrenia may reflect dysfunction of frontostriatal circuitry that subserves WM. Future studies will elucidate the contribution of the anatomical components of this circuitry to WM deficits.

Schizophrenic subjects activate dorsolateral prefrontal cortex during a working memory task, as measured by fMRI.

BACKGROUND: Neuroimaging studies of schizophrenic subjects performing working memory (WM) tasks have demonstrated a relative hypoactivity of prefrontal cortex compared with normal subjects. METHODS: Using functional magnetic resonance imaging (fMRI), we compared dorsolateral prefrontal cortex (DLPFC) activation in 12 schizophrenic and 10 normal subjects during rewarded performance of a WM task. Subjects performed a modified version of the Sternberg Item Recognition Paradigm (SIRP), a continuous performance, choice reaction time (RT) task that requires WM. We compared a high WM load condition with a nonWM choice RT condition and with a low WM load condition. RESULTS: Schizophrenic subjects performed the tasks better than chance but worse than normal subjects. They showed greater activation than normal subjects in the left DLPFC but did not differ in the right DLPFC or in the control region. In the schizophrenic group, left DLPFC activation was inversely correlated with task performance, as measured by errors. CONCLUSIONS: These findings contrast with previous studies that demonstrated task-related hypofrontality in schizophrenia. Task parameters that may contribute to this difference are discussed. We hypothesize that the performance and activation differences we observed are also manifestations of prefrontal dysfunction in schizophrenia. They reflect inefficient functioning of the neural circuitry involved in WM.

Secondary elevation of extracellular neurotransmitter amino acids in the reperfusion phase following focal cerebral ischemia.

The purpose of this study was to evaluate amino acid neurotransmitter dynamics in the reperfusion phase after transient cerebral ischemia. In vivo microdialysis was used to measure extracellular amino acid levels in a rabbit model of focal ischemia. During 30 min of transient ischemia (n = 5), small but significant (p < 0.05) increases in glutamate, aspartate, gamma-aminobutyric acid (GABA), and taurine were noted. These elevations rapidly returned to baseline levels upon recirculation and remained constant for up to 5.5 h of reperfusion. In rabbits subjected to 2 h of transient ischemia (n = 5), two phases of amino acid release were seen. During ischemia, large (5- to 50-fold) elevations in glutamate, aspartate, GABA, and taurine occurred, as expected. These elevations rapidly normalized upon unocclusion. However, significant (p < 0.05) secondary elevations in glutamate, aspartate, and GABA occurred after 2-4 h of reperfusion. Regression analysis demonstrated significant correlations between primary (ischemic) and secondary (reperfusion) efflux. In permanent ischemia (n = 5), amino acid levels remained elevated throughout the entire experiment. Secondary elevations in excitatory amino acids may further contribute to the excitotoxic cascade during reperfusion.

Inadequacy of sample sizes in clinical trials of laboratory parameters attributable to invalid statistical assumptions.

Clinical trials often determine the sample size based on the use of statistical methods such as analysis of variance, t tests, and rank sum tests, which compare mean or median values. The resulting studies rarely are big enough to show that the method is based on mistaken assumptions. Data from a recent clinical trial of nephrotoxicity associated with the use of contrast agents during angiography found a significant difference on the order of the difference that previous studies had intended to detect. It also showed that a central assumption does not apply to changes in serum creatinine. As a result, the previous studies had considerably lower power than believed. Their lack of significance reflected only the mistaken assumption. Analysis of variance, t tests, and rank sum tests may be just as invalid for other clinical parameters. Lack of significance cannot be automatically taken to imply a small treatment effect.

Test-retest reliability of a functional MRI working memory paradigm in normal and schizophrenic subjects.

OBJECTIVE: Repeated functional magnetic resonance imaging (fMRI) studies of schizophrenic subjects may identify brain activity changes in response to interventions. To interpret the findings, however, it is crucial to know the test-retest reliability of the measures used. METHOD: The authors scanned seven normal subjects and seven schizophrenic subjects on two occasions during performance of a working memory task. They quantified the reliability of task performance and brain activation. RESULTS: In both groups, task performance was reliable, and all a priori regions were activated in group-averaged test and retest data. In individual schizophrenic subjects, however, indices of cognitive activation were not reliable across sessions. Normal subjects showed reasonable reliability of activation. CONCLUSIONS: Even given reliable task performance, stable clinical status, and a stable pattern of group-averaged activation, individual subjects showed unreliable brain activation. This suggests that repeated fMRI studies of schizophrenia should control for sources of variation, both artifactual and intrinsic.

Tolerance of autologous and allogeneic bone grafts to therapeutic radiation in humans.

PURPOSE: To examine the effect of perioperative irradiation on bone graft healing and functional integrity. METHODS AND MATERIALS: Fifty-five bone grafts (10 autologous and 45 allogeneic) performed between 1978 and 1995 were evaluated retrospectively. Sixteen received preoperative radiation, 11 received postoperative, and 13 were treated with a combination of pre- and postoperative radiation. Fifteen nonirradiated grafts were randomly selected to serve as controls. Twenty-three of the grafts were placed in patients who received chemotherapy in the perioperative period. Functional graft survival and radiographic healing quality were evaluated. RESULTS: Overall rates of graft survival at 1 year were 89% for autografts and 79% for allografts. Graft survival rates were 86% and 68% at 1 and 5 years for the irradiated group, and 67% and 58% for the control group. No significant difference was seen in the Kaplan-Meier graft survival curves of the two groups. There was a nonsignificant trend toward improved radiographic healing quality in the control group. No significant differences in outcome based on treatment chronology were found with survival rates of 88% for preoperative treatment and 100% for postoperative treatment. No relation between outcome and bone dose (preoperative + postoperative dose), graft dose (postoperative dose), or mean dose/day was found. There was a trend (p = 0.0525) toward worse outcome seen in the Kaplan-Meier curves of patients who received chemotherapy. This difference, however, was not seen in the 1-year survival rates or healing quality. Tobacco use tended toward predicting failure, with 63% graft survival compared to 85% in nonsmokers (p = 0.09). Healing quality was significantly lower in the smoking group. CONCLUSION: The low failure rate of grafts in irradiated sites, overall and compared to controls from this study and relevant literature, as well as the lack of dose and time effects, does not support significant deviation from the indicated treatment regimen for patients who have received or are expected to receive a graft. The trend toward decreased quality of radiographic bone healing, and data published in relevant literature indicating improved healing when radiation is withheld until 3-4 weeks postoperatively suggest this delay should be attempted when not expected to otherwise compromise patient outcome. A nonsignificant trend only for the effect of chemotherapy on bone grafts was seen, thus we do not recommend changes in its use as appropriate for disease management other than a preference against use during the immediate perioperative period.

The futility of the chest radiograph in the febrile infant without respiratory symptoms.

OBJECTIVE: Major pediatric textbooks advocate a chest radiograph as part of the diagnostic evaluation for a sepsis workup for febrile infants less than 3 months old. Very few studies have addressed the value of performing a chest radiograph in this situation. Two studies previously published lack the numbers to statistically justify a conclusion about the need to perform a chest radiograph in the febrile infant. METHODS: Evaluated were 197 febrile infants 3 months old or less with a history, physical examination, chest radiograph, and other laboratory studies to determine the cause of their fever. This group of infants was combined with the group of infants from two similar studies published previously in the literature using cumulative meta-analysis. The combined group resulted in 617 infants. RESULTS: The combined group of infants had 361 infants who had no clinical evidence of pulmonary disease on history or physical examination. All 361 infants had normal chest radiograph. These results gave a 95% confidence interval that the chance of a positive chest radiograph in a patient with no pulmonary symptoms would occur less than 1.02% of the time. CONCLUSIONS: The generally advocated policy of obtaining a chest radiograph as part of the sepsis workup in febrile infants should be discontinued, and chest radiographs should be obtained only in febrile infants who have clinical indications of pulmonary disease.

Multicenter trial of ionic versus nonionic contrast media for cardiac angiography. The Iohexol Cooperative Study.

Contrast agents used for cardiac angiography are different in regard to ionicity, osmolality and physiologic effects. The nonionic contrast media have been shown to have less toxic effects and a better safety profile than do higher osmolar agents. To better assess this risk, clinically stable patients undergoing cardiac angiography were stratified according to the presence of diabetes mellitus, and level of serum creatinine, and then randomized to receive either iohexol (Omnipaque 350) or sodium meglumine diatrizoate (Renografin 76). All adverse events that occurred during and immediately after angiography were tabulated. A multivariate model was used to identify patients at increased risk for adverse outcome. The 1,390 patients were randomized to iohexol (n = 696) or diatrizoate (n = 694). Significant differences were found in the number of patients with contrast media-related adverse (iohexol vs diatrizoate: 10.2 vs 31.6%; p < 0.001) and cardiac adverse (7.2 vs 24.5%; p < 0.001) events. Severe reactions and the need for treatment were more frequent with diatrizoate than with iohexol, but there was no difference in the incidence of death. The presence of New York Heart Association classification 3 or 4 and serum creatinine > or = 1.5 mg/dl predicted a higher incidence of adverse events as a result of contrast media alone. Use of iohexol is associated with a lower incidence of all types of adverse events during cardiac angiography than is diatrizoate.

A multicentre evaluation of the laser assisted ratio analyser (LARA): a novel device for measurement of 13CO2 in the 13C-urea breath test for the detection of Helicobacter pylori infection.

BACKGROUND: The laser assisted ratio analyser (LARA) was developed as a novel device to measure 13CO2 in the urea breath test for the detection of H. pylori infection. The analyser was tested in a prospective multicentre study in 444 patients in North America (Phase 1) followed by second study involving 160 patients (Phase 2). METHODS: Patients undergoing endoscopy for clinical indications had antral and gastric biopsies taken for histological examination, culture and CLO test. One hour after endoscopy, a baseline breath sample was obtained, 100 mg of 13C-urea were ingested and breath samples were obtained at 30 and 60 min post ingestion. Data obtained with the LARA were compared with the results of culture, rapid urease testing and central pathology in two different combinations {reference standards}. The study was conducted in two phases: in Phase 2, a modification was made to the LARA that improved the removal of water vapour from the breath sample. RESULTS: In Phase I, data from 331 patients were analysed using a cut off of (delta) 7.8 +/- 0.8, the sensitivity of the method was 91.7% and the specificity was 86.5%, using the reference standard of 2 of 3 tests (CLO, culture or histology) being positive. Positive and negative predictive values were, respectively, 85.2% and 92.5%. In Phase 2 of the study, 160 patients were enrolled and 141 patients were analysed using the same standards. We used the same reference standards but with a cut off of (delta) 6.1 +/- 0.6. The sensitivity and specificity increased to 96.8% and 98.6%, respectively. Positive and negative predictive values were, respectively, 98.4% and 97.3%. The detection rates for H. pylori were similar in patients with peptic ulcer or H. pylori associated gastritis. CONCLUSIONS: The LARA provides an accurate non-invasive means of detecting 13CO2 in the 13C-urea breath test for H. pylori in a multicentre clinical environment that compares well with invasive 'gold standard' methods.

Calculation of tissue attenuation with a clinical ultrasound unit.

RATIONALE AND OBJECTIVES: Five alternative methods for estimating tissue attenuation with a clinical ultrasound unit were evaluated. METHODS: Two homogeneous tissue mimicking phantoms (with known attenuations of 0.25 and 0.54 db/cm/MHz) and 22 human placentas were scanned. Attenuation coefficients were computed by linear regression of 1) L(f), the log spectral difference; 2) Fav (d), the average spectral frequency; 3) log[P(d)], the logarithm of the spectral power; 4) Fav (d) x log[P(d)]; and 5) (Fav(d) + log[P(d)])/2. RESULTS: Each of these five heuristics provided accurate estimates for the relative attenuations of the two phantoms. For placental tissue, method 3 provided better regression fits than methods 1 and 2. Methods 4 and 5 provide the best regression fits (P < .01). CONCLUSIONS: The combination of both frequency and power information in methods 4 and 5 compensates, in part, for nonlinearities introduced by tissue heterogeneity. A parameter that combines both frequency and time domain information is likely to provide more reliable estimates of attenuation than power or frequency measurements alone.

Effect of focal zone on a curved array transducer.

RATIONALE AND OBJECTIVES: This study investigates the effect of electronic focusing of a linear array transducer on received ultrasound signal. METHODS: Two tissue-mimicking phantoms of known attenuation were imaged with a focal distance that was varied from 2 to 12 cm. Received signal was processed by Fourier analysis to compute average frequency and power as functions of depth within the phantom. RESULTS: Average received frequency increases dramatically over the first centimeter from the transducer and then decreases linearly to 8 to 11 cm with a slope proportional to the phantom's attenuation. Average frequency from greater depths decreases more rapidly and is dependent on the focal zone. Received power peaks at approximately the focal depth and decays exponentially beyond that level; the decay constant is proportional to the phantom's attenuation but independent of focusing. CONCLUSIONS: The frequency and power of received ultrasound signal are altered by electronic focusing in ways that may significantly influence both tissue characterization and clinical imaging applications.

Anticoagulant effects of nonionic versus ionic contrast media in angiography syringes.

To determine whether nonionic contrast media present a clotting hazard when plastic or glass injection syringes are contaminated with aspirated blood, we evaluated two nonionic (iohexol and iopamidol) and two ionic (ioxaglate and diatrizoate) contrast agents. We used a blood:contrast media ratio of 2 mL:5 mL and ten normal donors, each studied at 10, 20, 30, and 60 minutes, a parallel study of clotting and fibrinopeptide A (FPA) generation in plastic tubes, and life table analysis to estimate more accurately donor-based early clotting probabilities. While ionic contrast media are stronger anticoagulants, both nonionic and ionic media retard clotting in plastic tubes, and clotting in plastic and glass angiography syringes in comparison to saline controls. A clotting probability of 1% for nonionic agents in plastic syringes was not reached until a time (mean +/- SD) of 21.5 +/- 3.2 minutes. This contrasts with a time of 8.7 +/- 2.5 minutes for saline control. With plastic syringes, no clotting at all was observed at 10 and 20 minutes with either class of agents. Neither class of agents hastened the generation of FPA. We found no evidence, therefore, that nonionic agents either cause clots or are procoagulant.