Evaluation of a commercial radiochromatography module as an arterial blood activity monitor.

Input functions required for positron emission tomography (PET) tracer kinetic modeling are often obtained from arterial blood. In some situations, using short-lived radiotracers, e.g. [(15)O]water, rapid sample handling is required. A method used at several facilities is to pump blood through a detector system at a constant rate. We investigate the suitability of a commercial radiochromatography module (IN/US Posi-RAM) for this new use. The Posi-RAM consists of two 2.5 cm (length) x 2.5 cm (diameter) cylindrical bismuth germanate (BGO) detectors that can operate in coincidence mode. Arterial blood is transported through the system via a length of tubing with flow rate controlled by a peristalsis pump. A custom-counting loop and support frame were designed for the Posi-RAM for PET studies. System sensitivity was determined to be 1.1 x 10(4) cps/(MBq ml(-1)). Dead time as a function of count-rate was found to be less than 1% for concentrations below 3.5 MBq ml(-1), a range encompassing all human-study values. In a human study, the performance of the device was found to be similar to that of the facility's current blood monitor (Siemens Fluid Monitor). We conclude that the Posi-RAM has the necessary sensitivity and count-rate capabilities to be used as a real-time blood activity monitor.

Attenuation correction for a combined 3D PET/CT scanner.

In this work we demonstrate the proof of principle of CT-based attenuation correction of 3D positron emission tomography (PET) data by using scans of bone and soft tissue equivalent phantoms and scans of humans. This method of attenuation correction is intended for use in a single scanner that combines volume-imaging (3D) PET with x-ray computed tomography (CT) for the purpose of providing accurately registered anatomical localization of structures seen in the PET image. The goal of this work is to determine if we can perform attenuation correction of the PET emission data using accurately aligned CT attenuation information. We discuss possible methods of calculating the PET attenuation map at 511 keV based on CT transmission information acquired from 40 keV through 140 keV. Data were acquired on separate CT and PET scanners and were aligned using standard image registration procedures. Results are presented on three of the attenuation calculation methods: segmentation, scaling, and our proposed hybrid segmentation/scaling method. The results are compared with those using the standard 3D PET attenuation correction method as a gold standard. We demonstrate the efficacy of our proposed hybrid method for converting the CT attenuation map from an effective CT photon energy of 70 keV to the PET photon energy of 511 keV. We conclude that using CT information is a feasible way to obtain attenuation correction factors for 3D PET.

Test-retest variability of serotonin 5-HT2A receptor binding measured with positron emission tomography and [18F]altanserin in the human brain.

The role of serotonin in CNS function and in many neuropsychiatric diseases (e.g., schizophrenia, affective disorders, degenerative dementias) support the development of a reliable measure of serotonin receptor binding in vivo in human subjects. To this end, the regional distribution and intrasubject test-retest variability of the binding of [18F]altanserin were measured as important steps in the further development of [18F]altanserin as a radiotracer for positron emission tomography (PET) studies of the serotonin 5-HT2A receptor. Two high specific activity [18F]altanserin PET studies were performed in normal control subjects (n = 8) on two separate days (2-16 days apart). Regional specific binding was assessed by distribution volume (DV), estimates that were derived using a conventional four compartment (4C) model, and the Logan graphical analysis method. For both analysis methods, levels of [18F]altanserin binding were highest in cortical areas, lower in the striatum and thalamus, and lowest in the cerebellum. Similar average differences of 13% or less were observed for the 4C model DV determined in regions with high receptor concentrations with greater variability in regions with low concentrations (16-20%). For all regions, the absolute value of the test-retest differences in the Logan DV values averaged 12% or less. The test-retest differences in the DV ratios (regional DV values normalized to the cerebellar DV) determined by both data analysis methods averaged less than 10%. The regional [18F]altanserin DV values using both of these methods were significantly correlated with literature-based values of the regional concentrations of 5-HT2A receptors determined by postmortem autoradiographic studies (r2 = 0.95, P < 0.001 for the 4C model and r2 = 0.96, P < 0.001 for the Logan method). Brain uptake studies in rats demonstrated that two different radiolabeled metabolites of [18F]altanserin (present at levels of 3-25% of the total radioactivity in human plasma 10-120 min postinjection) were able to penetrate the blood-brain barrier. However, neither of these radiolabeled metabolites bound specifically to the 5-HT2A receptor and did not interfere with the interpretation of regional [18F]altanserin-specific binding parameters obtained using either a conventional 4C model or the Logan graphical analysis method. In summary, these results demonstrate that the test-retest variability of [18F]altanserin-specific binding is comparable to that of other PET radiotracers and that the regional specific binding of [18F]altanserin in human brain was correlated with the known regional distribution of 5-HT2A receptors. These findings support the usefulness of [18F]altanserin as a radioligand for PET studies of 5-HT2A receptors.

Correction for scatter in 3D brain PET using a dual energy window method.

A method for scatter correction using dual energy window acquisition has been developed and implemented on data collected with a brain-PET tomograph operated in the septa retracted, 3D mode. Coincidence events are assigned to (i) an upper energy window where both photons deposit energy between 380 keV and 850 keV or (ii) a lower energy window where one or both photons deposit within 200 keV and 380 keV. Scaling parameters are derived from measurements of the ratios of counts from line sources due to scattered and unscattered events in the two energy windows in head-sized phantoms. A scaled subtraction of the two energy windows produces a distribution of scatter which is smoothed prior to subtraction from the upper energy window. In phantoms, the correction was found to restore the uniformity, contrast and linearity of activity concentration. Relative activity concentrations were restored to within 7% of their true values in a multicompartment phantom. The method was found to provide accurate correction for scattered events arising from activity outside the direct detector field of view. In a three-compartment phantom containing water, 18F and 11C scanned in dynamic, multiframe mode, the half-lives of the two isotopes were restored to within 2% of their true value.

Reduced dose and improved image quality with a computerized line-scan radiography system.

Diode-array digital radiography (DADR) is a patented technology which shows promise for producing improved radiographic image quality while reducing the X-ray dose to the patient. DADR combines geometric scatter rejection with a scintillator and solid-state photodiode array detector of large dynamic range to create diagnostic X-ray images which makes efficient use of the patient dose. Engineering measurements were made to determine the basic characteristics of the system. Engineering measurements were made to determine the basic characteristics of the system. A number of image postprocessing techniques were examined for further improving the image quality of the DADR system. Unsharp masking, local contrast stretching, and modified local contrast stretching were used. The modified local contrast stretching has produced the best results to date, with image quality exceeding that of standard film/screen chest images. Images have been postprocessed using facilities of the Pittsburgh Supercomputer Center.

Primary CT diagnosis of abdominal masses in a PACS environment.

Whether the display medium--film versus cathode ray tube (CRT)--affects observer performance during interpretation of computed tomographic (CT) images is an important research issue in these times of implementation and growth of picture archiving and communications systems in radiology. The authors performed a multiobserver receiver operating characteristic (ROC) study to determine the performance of radiologists who read abdominal CT studies displayed on film, as well as on a high-resolution workstation (video monitor) that made use of three different display modes. A total of 166 examinations were evaluated by eight radiologists, who recorded their ordinal confidence ratings of the demonstration of presence or absence of abdominal masses. ROC analysis showed small differences in the confidence ratings assigned by individual readers for the detection and interpretation tasks. Results for the group as a whole showed no significant reduction or improvement in observer performance when ratings for any one of the workstation display modes were analyzed. The results of this study demonstrate that current CRT display technology is adequate for enabling the primary detection of abdominal masses with CT examinations.

The effect of grip strength on radial bone in postmenopausal women.

This communication explores the correlation in 255 postmenopausal women of grip strength to bone tissue density (BTD) and cross-sectional area (CSArea) of the radius. While grip strength correlated cross-sectionally with the baseline measures of both BTD and CSArea, grip strength affected differentially the changes that transpired in the two bone parameters over the 3 years of the study. Thus, the increases in the CSArea of the radius were significantly enhanced by higher grip strength, while BTD losses were not. Since the power of muscle contraction is a factor in the mechanical loading of a bone, it is argued that the differential effects of grip strength on the two bone parameters of the radius suggest that moderate loading can effect favorable changes in the geometry of the bone, without necessarily affecting changes in BTD.

Endogenous estrogen levels and calcium intakes in postmenopausal women. Relationships with cortical bone measures.

To examine the interactions between hormone levels and calcium with cortical bone, we have attempted to combine risk factors for the development of peak skeletal mass with factors that may be related to the maintenance of bone integrity after menopause. A total of 174 postmenopausal women participated in our study. There was little relationship found between androgen hormones and radial bone density. Estrone levels were independently related to radial bone density. Examination of the relationship of calcium intake to bone revealed a protective effect solely in women who reported high "lifetime" calcium intakes. Taking calcium and estrone together revealed an additive relationship between the two factors, in that women with high estrone and high calcium levels had significantly greater bone density than women with less calcium and/or estrone. The results suggest that a lifetime of adequate calcium intake coupled with adequate levels of serum estrogens could maximize bone density after menopause.

The effects of walking on the cross-sectional dimensions of the radius in postmenopausal women.

This report deals with the analysis of data from a 3-year clinical trial on the effect of walking on postmenopausal bone loss. Two hundred fifty-five women, with an average age of 57 at entry, were randomized into two groups, a walking and a control group. Bone measures in the shaft of the radius were carried out with a CT scanner in search of generalized skeletal effects rather than effects localized to the bones of the leg. Although bone density losses were comparable in the two randomized groups, changes in the cross-sectional area of the radius were significantly greater in the walkers with high grip strength (greater than 25 Kg) than in the controls with comparable high grip strength which corresponded to the upper half range of the grip-strength distribution. It is concluded that the moderate activity of walking exerted systemically positive effects on the radius which, within the protocol of the study, could be substantiated only when synergized with inherent muscle strength.

Digital radiography of the chest by self-scanning linear diode arrays.

Diode array digital radiography DADR is a method of radiographic imaging that combines the advantages of computer technology with self-scanning linear diode arrays. These digital images are superior to those obtained by film in recording and displaying information in the lightest and the darkest areas of the film, resulting in a balanced image of the entire thorax without compromising detail, and at reduced radiation dose. This is a direct result of the wide dynamic range, high contrast sensitivity, fiber optic coupling, small diode size, short exposure time, and rejection of scattered x-rays of the system coupled with digital post-processing enhancement of the image displayed at 1024 X 1024 pixels.

The relationship of endogenous estrogen to bone density and bone area in normal postmenopausal women.

The relationship of endogenous concentrations of estrogen, in particular estrone, to the dominant radial bone density and bone area was examined in 78 normal postmenopausal women (mean age 57 years). The women were a subset of a population participating in a clinical trial designed to determine the effects of walking on bone loss. The data reported here were collected at baseline prior to randomization. Radial cortical bone density and bone area were measured at 30 per cent of the distance between the wrist and the elbow in the dominant arm. Estrone levels obtained by extraction and column chromatography were measured by radioimmunoassay. Estrone concentrations were cross-sectionally related to both radial bone density (r = 0.39, p less than 0.001) and bone area (r = 0.39, p less than 0.001). This relationship was independent of age, number of years since onset of menopause, and degree of obesity. In multiple regression analysis, estrone levels accounted for 15 per cent of the variance in bone density and bone area in this population. These results suggest that measurement of estrone in normal postmenopausal women may assist in the identification of women who are at high risk for osteoporosis and, thus, possible candidates for estrogen replacement therapy.

Diode array digital radiography: initial clinical experience.

Initial clinical results are described for a new method of digital radiography based on high-detail self-scanning linear diode arrays which overcome many of the limitations of present film or other digital methods. The technique uses a fan-shaped x-ray beam to produce a nearly scatter-free image on a phosphor strip that is fiber-optically coupled to six self-scanning arrays of light-sensitive diodes spaced 0.025 mm, thus providing 6,144 discrete sensors across the field of view. Because these diodes have a greatly expanded dynamic range and operate at very low noise, it becomes possible to visualize small density differences or contrast below 1% both in the light and dark areas of the image. Because of the efficiency of detection and display, radiation doses can be reduced for a given information content. Our preliminary clinical studies have shown to broad application of our method in examining the chest and abdomen and in performing intravenous digital arteriography.

Electronic radiography in neurosurgery.

The authors describe the use of electronic radiography or short-exposure fluoroscopy with concurrent video recording of images in neurosurgery. The technique is applicable to all neurosurgical procedures in which fluoroscopy is used, such as transphenoidal surgery, trigeminal RF rhizolysis, percutaneous cordotomy, etc. With the use of subtraction techniques and intra-operative angiography, vascular maps of the cerebral vascular system can be made that allow the surgeon to puncture or to avoid vascular structures during stereotaxic procedures. Besides a great reduction in radiation exposure, this technique offers new advantages and potential for neurosurgical and neuroradiological interventional procedures.

Evaluation of benefits and risks of breast cancer screening.

Benefit/risk ratios derived by another study group for a population screened at a breast cancer detection center during the first year of operation are analyzed. The authors of the present paper look at the problem in a somewhat different manner. Benefit/risk ratios derived using this approach are significantly lower than those reported in the previous study. The results of the present study indicate that annual mass screening of women under the age of 50 is of questionable value.

An evaluation of a high resolution closed-circuit television link in a hospital radiology department.

We have installed and developed a high resolution closed-circuit television system for transmission of radiographic film images from the emergency room in our hospital to the reading room in our radiology department. Using this system, the radiologist can consult promptly on all films and he has increased efficiency. To transmit high detail images, our television system uses a high resolution vidicon camera with a scan rate of 1029 lines and with a limiting resolution of 1200 TV lines. To further increase the overall diagnostic value of our system, we have added remote controls for changing the magnification, illumination and position of the film. In a preliminary clinical trial, seven radiologists were each shown 27 patient film sets transmitted through the television system and then viewed directly on a conventional view box. An analysis of variance of the accuracy rates in each method showed a statistical difference in methods. Even though the error rate was slightly higher using closed-circuit system, radiologist performance was of acceptable accuracy when considering the advantages of the system. In addition, many of the factors reducing the TV system performance have been eliminated or controlled, and further experiments should reflect an even smaller difference between the two methods.