Interreader variability and predictive value of US descriptions of solid breast masses: pilot study.

RATIONALE AND OBJECTIVES: This study evaluated the specificity of ultrasound (US) characteristics of solid breast lesions and the interreader variability in their interpretation. MATERIALS AND METHODS: In 61 patients, 70 sonographically visible solid masses, scheduled for biopsy because of findings from conventional imaging, were prospectively and sequentially accrued for evaluation. Three readers interpreted the sonograms and described the solid masses in terms of established US characteristics. The specificity and positive predictive value (PPV) for each characteristic were calculated by comparing US findings with biopsy findings, and interreader variability was evaluated. Five assessment categories were developed to guide recommendations for patient care. The relative performance of each reader was assessed by measuring the PPV for each assessment category and by measuring the area under the receiver operating characteristic curve. RESULTS: The specificity and PPV were calculated for all characteristics and for each reader. The average specificities of the three readers for the most frequently used six characteristics were as follows: spiculation, 97%+/-5 (standard deviation); taller than wide, 91%+/-4; central shadowing, 77%+/-1; markedly hypoechoic, 86%+/-5; duct extension, 95%+/-5; and microlobulation, 84%+/-3 (overall average specificity, 88.5%). The average PPVs for categories II-V were 5%, 10%, 63%, and 94%, respectively. The readers' interpretations were similar and correlated well. CONCLUSION: The proposed US recommendation system is an accurate predictor of histologic findings. A sonographic classification lexicon should prove valuable.

Renal blood flow changes induced with endothelin-1 and fenoldopam mesylate at quantitative Doppler US: initial results in a canine study.

PURPOSE: To evaluate quantitative Doppler ultrasonography (US) for assessing renal blood flow changes induced with endothelin-1 (ET-1) and fenoldopam mesylate in conscious dogs. MATERIALS AND METHODS: A blood flow probe was surgically implanted around the renal artery in eight adult dogs. Color and power Doppler US images were acquired in conscious restrained dogs during intravenous infusion of ET-1 and fenoldopam mesylate. Simultaneous with imaging, blood flow through the renal artery was measured with the implanted probe. The color level of the images within the region representing the kidney was analyzed to derive flow indices. These indices were compared with direct-flow measurements. RESULTS: The flow indices, color-weighted flow area (CWFA), and percentage of area of color, derived from color and power Doppler US images, correlated linearly with direct flow. The mean color level of color and power Doppler US images correlated weakly with direct flow. Pre- versus postinfusion CWFA decreased with all ET-1 infusions (P < or =.032). Infusion of fenoldopam mesylate increased CWFA in all cases (P < or =.032). CONCLUSION: Quantitative Doppler US enabled successful measurement of the flow changes induced with ET-1 and fenoldopam mesylate. Quantitative Doppler US is potentially useful as a noninvasive surrogate endpoint in evaluating the action of various therapeutic agents.

Value of iterative reconstruction, attenuation correction, and image fusion in the interpretation of FDG PET images with an integrated dual-head coincidence camera and X-ray-based attenuation maps.

PURPOSE: To compare lesion detectability on 2-[fluorine-18]fluoro-2-deoxy-D-glucose (FDG) positron emission tomographic (PET) images obtained with a dual-head coincidence (DHC) gamma camera equipped with an integrated x-ray tube-based transmission system (a) with images reconstructed with filtered back projection (FBP) and those reconstructed with an iterative reconstruction algorithm based on coincidence-ordered subsets expectation maximization (COSEM), (b) with images reconstructed without and with attenuation correction (AC), and (c) with images reconstructed without and with image fusion for anatomic mapping. MATERIALS AND METHODS: Thirty-five patients known or suspected to have malignancy underwent initial imaging with a dedicated positron emission tomography (PET) unit after injection of 10 mCi (370 MBq) of FDG. Transmission computed tomographic (CT) scans and FDG emission images were then obtained with the DHC camera. The proportion of lesions detected on the various sets of FDG DHC images was determined by using FDG PET as the standard of reference. Imaging findings were correlated with those from histologic examination and clinical follow-up, in consultation with the respective referring physicians. RESULTS: FDG PET depicted 78 lesions, 29 of which were equal to or less than 1.5 cm in diameter. FDG DHC depicted 52 of the 78 (67%), 59 of 78 (76%), and 61 of the 78 (78%) lesions, respectively, when image reconstruction was performed with FBP without AC, COSEM without AC, and both COSEM and AC. The detection rate of lesions 1.5 cm or smaller was better with COSEM and AC than with FBP (55% vs 34%, respectively). In addition, COSEM and AC allowed more confidence in the interpretation. None of these differences, however, were significant. Fusion of CT scans and FDG DHC images obtained with COSEM and AC allowed localization of lesions to the skeleton in three patients and to the liver versus adjacent bowel in three patients. Image fusion was especially helpful for localizing lesions in the neck in five patients. Anatomic mapping on fusion images was clinically relevant in 11 patients (31%). CONCLUSION: The COSEM reconstruction algorithm should replace FBP when available. Functional anatomic mapping improved lesion localization in one-third of the patients studied.

Survey of use of ST-segment monitoring in patients with acute coronary syndromes.

BACKGROUND: Although effective for assessing ongoing myocardial ischemia, ST-segment monitoring may be underused. OBJECTIVES: To determine the proportion of cardiac units in the United States that use ST-segment monitoring, hospital and unit characteristics associated with its use, how units use such monitoring with respect to research recommendations, if units that use ST-segment monitoring find it clinically useful and easy to use, and why some units are not using this type of monitoring. METHODS: A survey on ST-segment monitoring was mailed to a random sample of 500 cardiac nurse managers and clinical nurse specialists. RESULTS: Of the final 192 respondents, 104 (54.2%) reported that they were using ST-segment monitoring. Monitor brand was the only characteristic associated with use of this monitoring (P = .03). On units that used ST-segment monitoring, patients were monitored if they had myocardial infarction (81%), unstable angina (79.6%), or possible myocardial infarction (78.6%) and after percutaneous transluminal coronary angioplasty (47.6%). Leads were chosen according to unit protocol (60.2%) and 12-lead electrocardiographic findings (48.5%); leads II (95.0%) and V1 (75.2%) were used most often. The majority of units that use ST-segment monitoring agreed that it is clinically useful (83%) and easy to use (56%). Among the units not using ST-segment monitoring, the most common reason was that physicians were not interested (27.1%). CONCLUSIONS: ST-segment monitoring is not routinely used; when it is, research recommendations are often not followed. Increased awareness is needed among cardiac nurses and physicians of the clinical usefulness and proper use of ST-segment monitoring.

Instrumentation for coincidence imaging with multihead scintillation cameras.

Positron emission tomography (PET) has been used as a tool by investigators for many years to study metabolic processes in the body primarily with the radiopharmaceutical 18-fluordeoxyglucose. However, use of this technology has not been widespread because of the high expense of the equipment and its limitation to the imaging of positron emitters only. Recent improvements in scintillation camera technology have now made it possible to produce hybrid multihead cameras that can function in a coincidence mode for the detection of the annihilation radiation from positron emitters and in the normal mode for routine single-photon imaging. Although still limited in sensitivity, these camera systems continue to be improved and the recent addition of iterative reconstruction algorithms and attenuation correction capability have resulted in significant improvements in image quality. The integration of a low resolution computed tomography (CT) scanner with a dualhead camera by 1 manufacturer now makes it possible to perform attenuation correction and image fusion of anatomy and function into 1 image to improve the anatomic localization of abnormalities detected with coincidence imaging. Investigators continue to work on improved electronics and new types of detectors to further improve the sensitivity of these systems. These developments coupled with continued improvements in PET technology have resulted in the availability of a broad spectrum of systems for the investigator to consider when purchasing a system with positron imaging capability.

18-Fluorodeoxyglucose imaging with positron emission tomography and single photon emission computed tomography: cardiac applications.

The assessment of myocardial viability has become an important aspect of the diagnostic and prognostic work-up of patients with ischemic cardiomyopathy. Although revascularization may be considered in patients with extensive viable myocardium, patients with predominantly scar tissue should be treated medically or evaluated for heart transplantation. Among the many viability tests, noninvasive assessment of cardiac glucose use (as a marker of viable tissue) with F18-fluorodeoxyglucose (FDG) is considered the most accurate technique to detect viable myocardium. Cardiac FDG uptake has traditionally been imaged with positron emission tomography (PET). Clinical studies have shown that FDG-PET can accurately identify patients with viable myocardium that are likely to benefit from revascularization procedures, in terms of improvement of left ventricular (LV) function, alleviation of heart failure symptoms, and improvement of long-term prognosis. However, the restricted availability of PET equipment cannot meet the increasing demand for viability studies. As a consequence, much effort has been invested over the past years in the development of 511-keV collimators, enabling FDG imaging with single-photon emission computed tomography (SPECT). Because SPECT cameras are widely available, this approach may allow a more widespread use of FDG for the assessment of myocardial viability. Initial studies have directly compared FDG-SPECT with FDG-PET and consistently reported a good agreement for the assessment of myocardial viability between these 2 techniques. Additional studies have shown that FDG-SPECT can also predict improvement of LV function and heart failure symptoms after revascularization. Finally, recent developments, including coincidence imaging and attenuation correction, may further optimize cardiac FDG imaging (for the assessment of viability) without PET systems.

Image fusion using an integrated, dual-head coincidence camera with X-ray tube-based attenuation maps.

UNLABELLED: The purpose of this study was to characterize a dual-head gamma camera capable of FDG imaging using coincidence detection and equipped with an integrated x-ray transmission system for attenuation correction, anatomic mapping, and image fusion. METHODS: Radiation dose (425 mrads skin dose) and tissue contrast (0.7% deviation from expected values) were assessed for the x-ray system. Registration of transmission and emission scans was validated using a hot sphere phantom and was verified in selected patient studies. RESULTS: Fusion of anatomic maps and FDG images allowed precise anatomic localization of lesions identified using dual-head coincidence imaging. CONCLUSION: The combined approach of x-ray attenuation, anatomic mapping, and image fusion with scintigraphic studies provides a new diagnostic tool for nuclear medicine and fertile ground for future research.

Quantitative vascularity of breast masses by Doppler imaging: regional variations and diagnostic implications.

Seventy-four biopsy proven breast masses were imaged by color and power Doppler imaging to evaluate vascular pattern of malignant and benign breast masses. The images were analyzed for vascularity. The measurements were made over the entire mass as well as regionally at its core, at its periphery, and in the tissue surrounding it. The surgical specimens were analyzed for microvessel density. The diagnostic performance of Doppler sonographic vascularity indices was evaluated by receiver operating characteristic analysis. The malignant masses were 14 to 54% more vascular than the benign masses. Both types of masses were more vascular by ultrasonography than the tissue surrounding them. Whereas benign masses were 2.2 times more vascular than the surrounding tissue, the malignant masses were 5.0 times more vascular. In a subset of patients the regional vascularity at the core, periphery, and surrounding tissue by Doppler imaging exhibited a strong correlation (R2 > 0.9) with the corresponding histologic microvessel density measurements. Although the malignant masses exhibited a strong gradient in vascularity, core > periphery > surrounding tissue, the benign masses had relatively uniform distribution of vascularity. The area under the receiver operating characteristic curve (A(Z)) for the Doppler indices ranged from 0.56 +/- 0.07 to 0.65 +/- 0.07. A nonlinear analysis including age-specific values of Doppler indices improved the diagnostic performance to A(Z) = 0.85 +/- 0.06. In conclusion, quantitative Doppler imaging when used in combination with a nonlinear rule-based approach has the potential for differentiating between malignant and benign masses.

Comparison of FDG PET and positron coincidence detection imaging using a dual-head gamma camera with 5/8-inch NaI(Tl) crystals in patients with suspected body malignancies.

The purpose of this study was to compare the diagnostic accuracy of fluorine-18 fluorodeoxyglucose (FDG) images obtained with (a) a dual-head coincidence gamma camera (DHC) equipped with 5/8-inch-thick NaI(Tl) crystals and parallel slit collimators and (b) a dedicated positron emission tomograph (PET) in a series of 28 patients with known or suspected malignancies. Twenty-eight patients with known or suspected malignancies underwent whole-body FDG PET imaging (Siemens, ECAT 933) after injection of approximately 10 mCi of 18F-FDG. FDG DHC images were then acquired for 30 min over the regions of interest using a dual-head gamma camera (VariCam, Elscint). The images were reconstructed in the normal mode, using photopeak/photopeak, photopeak/Compton, and Compton/photopeak coincidence events. FDG PET imaging found 45 lesions ranging in size from 1 cm to 7 cm in 28 patients. FDG DHC imaging detected 35/45 (78%) of these lesions. Among the ten lesions not seen with FDG DHC imaging, eight were less than 1.5 cm in size, and two were located centrally within the abdomen suffering from marked attenuation effects. The lesions were classified into three categories: thorax (n=24), liver (n=12), and extrahepatic abdominal (n=9). FDG DHC imaging identified 100% of lesions above 1.5 cm in the thorax group and 78% of those below 1.5 cm, for an overall total of 83%. FDG DHC imaging identified 100% of lesions above 1.5 cm, in the liver and 43% of lesions below 1.5 cm, for an overall total of 67%. FDG DHC imaging identified 78% of lesions above 1.5 cm in the extrahepatic abdominal group. There were no lesions below 1.5 cm in this group. FDG coincidence imaging using a dual-head gamma camera detected 90% of lesions greater than 1.5 cm. These data suggest that DHC imaging can be used clinically in well-defined diagnostic situations to differentiate benign from malignant lesions.

FDG PET and dual-head gamma camera positron coincidence detection imaging of suspected malignancies and brain disorders.

UNLABELLED: The purpose of the study was to compare the diagnostic accuracy of fluorodeoxyglucose (FDG) images obtained with a dual-head coincidence gamma camera (DHC) with those obtained with a dedicated PET in a series of 26 patients. METHODS: Nineteen patients with known or suspected malignancies and 7 patients with neurological disorders underwent PET imaging after injection of approximately 10 mCi of FDG. Whole-body imaging was performed on 19 patients and brain imaging on 7 patients. DHC images were then acquired for 30 min over the region of interest using a dual-head gamma camera equipped with 3/8-in.-thick NaI(TI) crystals and parallel slit-hole collimators. The images were reconstructed in the normal mode, using photopeak/photopeak, photopeak/Compton and Compton/photopeak coincidence events. RESULTS: Although the spatial resolutions of PET with a dedicated PET scanner and of DHC are in the same range, the lesion detectability remains superior with PET (4 mm for PET versus 13.5 mm for DHC in phantom experiments) with a contrast ratio of 5:1. This is most probably attributable to the higher sensitivity of PET (2238 coincidences/min/microCi for PET versus 89 coincidences/min/microCi for DHC). The pattern of uptake and interpretation for brain imaging was similar on both PET and DHC images in all patients. In the 19 oncology patients, 38 lesions ranging from 0.7 to 5 cm were detected by PET. DHC imaging detected 28 (73%) of these lesions. Among the 10 lesions not seen with DHC, 5 were less than 1.2 cm, 2 were located centrally within the liver and suffered from marked attenuation effects and 3 were adjacent to regions with high physiological activity. The nondetectability of some lesions with DHC compared with PET can be explained by several factors: (a) start of imaging time (mean+/-SD: 73+/-16 min for PET versus 115+/-68 min for DHC, leading to FDG decay to 6.75 mCi for PET and 5.2 mCi for DHC); (b) limited efficiency of a 3/8-inch-thick Nal(TI) crystal to detect 18F photons; (c) suboptimal two-dimensional reconstruction algorithm; and (d) absence of soft-tissue attenuation correction for centrally located lesions. CONCLUSION: FDG DHC imaging is a promising technique for oncological and brain imaging.

Fluorine-18-fluorodeoxyglucose cardiac imaging using a modified scintillation camera.

Conventional 201TI and hexakis 2-methoxy-2-isobutyl isonitrile studies are less accurate as compared to FDG PET in the prediction of functional recovery after revascularization in patients with injured but viable myocardium. The introduction of a dual-head variable-angle-geometry scintillation camera equipped with thicker crystals (5/8 in.) and high-resolution, ultrahigh-energy collimators capable of 511 keV imaging has permitted FDG SPECT to provide information equivalent to that of PET for the detection of injured but viable myocardium in patients with chronic ischemic heart disease. The development of standardized glucose-loading protocols, including glucose-insulin-potassium infusion and the potential use of nicotinic acid derivatives, has simplified the method of obtaining consistently good-to-excellent quality FDG SPECT cardiac studies. FDG SPECT may become the modality of choice for evaluating injured but viable myocardium because of enhanced availability of FDG, logistics, patient convenience, accuracy and cost-effectiveness compared to PET.

Introduction to nuclear physics.

Photons for counting or imaging applications in nuclear medicine result from several processes. Gamma rays are produced from excited state transitions after beta decay and electron capture. Annihilation photons result from positron decay. The de-excitation of the atom after electron capture results in the production of characteristic x rays or Auger electrons. Metastable state transitions result in gamma ray emission or internal conversion electrons. All radiopharmaceuticals used in diagnostic nuclear medicine applications are tagged with radionuclides that emit photons as a result of one of these processes.

High-energy (511-keV) imaging with the scintillation camera.

A dual-head scintillation camera has been adapted for high-energy (511-keV) imaging by extending the useful energy range and linearity maps to 560 keV, implementing high-energy sensitivity maps, and developing high-energy collimators. High-energy parallel-hole collimators have inferior spatial resolution and sensitivity relative to the low-energy, high-resolution collimators commonly in use. With high-energy parallel-hole collimators, phantom studies show that the limit for detectability of "hot" lesions is 1.5 cm and 1.3 cm in diameter or larger for 2-[fluorine-18]fluoro-2-deoxy-D-glucose (FDG) uptake ratios of 5:1 and 10:1, respectively, if one assumes adequate counting statistics. Dual-isotope, single-acquisition techniques for using technetium-99m methoxy isobutyl isonitrile and FDG have been developed and proved useful in identification of ischemic but viable myocardium. High-energy fan-beam collimators have superior spatial resolution but inferior sensitivity relative to low-energy, high-resolution collimators. Metabolic images of the brain obtained with FDG demonstrate spatial resolution comparable with that of positron emission tomography, but such studies are often limited by inadequate counting statistics.

Fluorine 18-labeled fluorodeoxyglucose myocardial single-photon emission computed tomography: an alternative for determining myocardial viability.

The identification of hibernating myocardium in patients with poor ventricular function has become increasingly important as investigators demonstrate an improvement in ventricular performance in patients with injured but viable myocardium who undergo surgical revascularization. Modifications of 201Tl redistribution protocols and rest/stress 99mTc-labeled hexakis-2-methoxy-2-methyl propylisonitrile perfusion studies continue to underestimate myocardial viability compared with resting 18F-labeled fluorodeoxyglucose (18FDG) positron emission tomography. The combined data from multiple investigators suggest that 18FDG single-photon emission computed tomography used in combination with cardiac perfusion agents, either sequentially or with simultaneous dual-isotope acquisition, may provide an acceptable alternative to positron emission tomographic imaging for the detection of hibernating myocardium.

Detection of malignancies with SPECT versus PET, with 2-[fluorine-18]fluoro-2-deoxy-D-glucose.

PURPOSE: To compare single photon emission computed tomography (SPECT) with 2-[fluorine-18]fluoro-2-deoxy-D-glucose (FDG) and positron emission tomography (PET) with FDG to evaluate malignancies. MATERIALS AND METHODS: PET and SPECT, with fluorine-18 sodium fluoride, were performed sequentially in a cylindric phantom that contained different size spheres with activity ratios of 5:1, 10:1, and 15:1. PET and SPECT were also performed in 24 patients with known or suspected malignancies. RESULTS: Sensitivities of PET and SPECT were 2,238 cpm/microCi (82.8 cpm/MBq) and 129 cpm/microCi (4.8 cpm/MBq), respectively (reconstructed spatial resolution, 7 and 17 mm, respectively [13-cm radius of rotation]). In the phantom studies, lesions of 1.5 and 1.3 cm or more in diameter were detected with a ratio of 5:1 and 10:1, respectively, and an information density of 150 counts per square centimeter. At FDG PET, 46 hypermetabolic lesions consistent with tumor were depicted in patients; at FDG SPECT, 36 (78%) were depicted. Sensitivity of FDG SPECT was 92% for detection of malignancies 1.8 cm or more in diameter seen at FDG PET. CONCLUSION: Findings at FDG SPECT can help differentiate benign from malignant lesions.

Rest myocardial perfusion/metabolism imaging using simultaneous dual-isotope acquisition SPECT with technetium-99m-MIBI/fluorine-18-FDG.

UNLABELLED: The purpose of this study was to develop a dual-isotope simultaneous acquisition (DISA) protocol using a multihead SPECT camera equipped with an ultrahigh-energy (UHE) collimator to evaluate simultaneously rest cardiac perfusion and metabolism with 99mTc-MIBI/18FDG. METHODS: Physical measurements were first performed with phantoms to develop the acquisition protocol. Fifteen patients underwent DISA-SPECT with 99mTc-MIBI/18FDG to validate the protocol. To evaluate the quality of the 99mTc-MIBI images acquired with the UHE collimator, four patients underwent a resting 99mTc-MIBI scan acquired with a high-resolution, low-energy collimator prior to DISA-SPECT. RESULTS: With a window of 20% for both photopeaks and a 99mTc/18F concentration ratio of 3.2:1, the spillover from 18F into the 99mTc window is 6% of the counts in the window for normal subjects. Phantom images clearly demonstrated defects measuring 2 x 1 and 2 x 0.5 cm. Technetium-99m-MIBI images obtained with the UHE and high-resolution collimators provided similar diagnostic information. Using a stenosis of > 70% as criteria to diagnose coronary artery disease, DISA-SPECT had a sensitivity of 100% and a positive predictive value of 93%. CONCLUSION: Simultaneous evaluation of rest myocardial perfusion/metabolism with a multihead SPECT camera equipped with an UHE collimator is possible using 99mTc-MIBI/18FDG with a dual-isotope simultaneous acquisition protocol.

Evaluation of myocardial ischemia using a rest metabolism/stress perfusion protocol with fluorine-18 deoxyglucose/technetium-99m MIBI and dual-isotope simultaneous-acquisition single-photon emission computed tomography.

OBJECTIVES: This study sought to develop a dual-isotope single-acquisition single-photon emission computed tomographic (SPECT) protocol using a multihead SPECT camera equipped with an ultra-high energy collimator to evaluate rest metabolism/stress perfusion simultaneously with fluorine-18 (F-18) deoxyglucose/technetium-99m (Tc-99m) 2-hexakis-2-methoxy-2-methylpropyl isonitrile (MIBI). BACKGROUND: The most accurate and logistic method of identifying injured but viable myocardium remains a diagnostic challenge. METHODS: Sixty-five patients were given 25 to 50 g of glucose and, after approximately 60 min, an injection of 370 MBq (10 mCi) of F-18 fluorodeoxyglucose. After a 35-min distribution phase, patients underwent exercise or pharmacologic stress followed by administration of 925 MBq (25 mCi) of Tc-99m MIBI. Five patients underwent F-18 fluorodeoxyglucose position emission tomography before dual-isotope SPECT: RESULTS: With a window of 20% for both photopeaks and a technetium-99m/fluorine-18 concentration of 3.2:1, the "spillover" from fluorine-18 into the technetium-99m window is < 6% of the total counts in the window in patients with a normal distribution of both radiopharmaceuticals. Phantom images clearly demonstrated cardiac defects measuring 2 x 1 and 2 x 0.5 cm. There was no significant difference in the images of the five patients who underwent both positron emission tomography and SPECT: Fifty-seven patients (mean [+/- SD] age 55 +/- 15 years, range 25 to 83; 38 men, 19 women) had satisfactory images and were included in the study. Twenty-one patients had normal study results; 15 had mismatched defects; 14 had matched defects; and 7 had both matched and mismatched defects. Twenty-three patients (mean age 54 +/- 6 years, range 30 to 83; 14 men, 9 women) underwent coronary angiography within 3 months of dual-isotope SPECT: There were seven normal studies, eight with mismatched defects, one with a matched defect and seven with matched and mismatched defects. When stenosis > 70% was used as the criterion for a diagnosis of coronary artery disease, dual-isotope SPECT had a sensitivity of 100%, specificity of 88%, positive predictive value of 93%, negative predictive value of 100% and an accuracy of 96%. CONCLUSIONS: Dual-isotope SPECT may provide an alternative, accurate, cost-effective method to nitrogen-13 ammonia/F-18 fluorodeoxyglucose positron emission tomography or thallium-201 reinjection for identifying injured or dysfunctional but viable myocardium.