Biomedical subjects

F H Fahey

Publications and source records attributed to F H Fahey.

At least 19 recordsLinked to original sources

PubMed1996

Lag phase quantification for solid gastric emptying studies.

UNLABELLED: This study compared the different calculation methods of the solid gastric emptying lag phase and evaluated the effect of the temporal sampling interval on the calculated value using the modified power exponential (MPE) method. METHODS: Twenty normal control subjects and 42 patients had anterior and posterior image acquisition on a multihead gamma camera, one frame per minute x 90. ROIs were selected for the stomach, gastric antrum and small bowel. Time-activity curves (TACs) were generated for anterior, posterior and geometric mean data. The lag phase was calculated using various methods such as transition point, starting index, first appearance of bowel activity (FABA), MPE and antral peak filling time. To determine the importance of the temporal sampling rate on the calculation of the lag phase by the MPE, intervals between 1 and 20 min were analyzed. RESULTS: The transition point, starting index and FABA correlated extremely high (r = > or = 0.92) in normal control subjects and patients. Normal lag phase values were mean 22-24 +/- 10 min for transition point, starting index and FABA compared with 47 +/- 18 min for the MPE method (p < 0.0001). The MPE correlated poorly with the other method (r = 0.74). Antral peak filling time correlated poorly (r = 0.47) with transition point, starting index and FABA, but somewhat better with the MPE (r = 0.70). Comparing 15-min versus 1-min sampling intervals using the MPE, 35% of subjects had values that differed by > or = 7.5 min and 10% had values differing by > or = 15 min. CONCLUSION: The lag phase calculated by the MPE correlated poorly with other methods, and its accuracy was limited by the rate of the temporal sampling. The transition point, starting index and FABA all highly correlated with each other; the latter is a particularly reliable physiological indicator and is easily quantified using a small-bowel TAC.

Adolescent↗

PubMed1995

Quantitation of SPECT performance: Report of Task Group 4, Nuclear Medicine Committee.

A comprehensive performance testing program is an essential ingredient of high-quality single-photon emission computed tomography (SPECT). Many of the procedures previously published are complicated, time consuming, or require a special testing environment. This Task Group developed a protocol for evaluating SPECT imaging systems that was simple, practical, required minimal test equipment, and could be performed in a few hours using processing software available on all nuclear medicine computers. It was designed to test rotational stability of uniformity and sensitivity, tomographic spatial resolution, uniformity and contrast, and the accuracy of attenuation correction. It can be performed in less than three hours and requires only a Co-57 flood source, a line source, and a tomographic cylindrical phantom. The protocol was used 51 times on 42 different cameras (seven vendors) by four different individuals. The results were used to establish acceptable ranges for the measured parameters. The variation between vendors was relatively small and appeared to reflect slight differences in basic camera performance, collimation, and reconstruction software. Individuals can use the tabulated values to evaluate the performance of individual systems.

Cobalt Radioisotopes↗

PubMed1995

Intermodality, retrospective image registration in the thorax.

UNLABELLED: The purpose of this study was to develop an accurate, retrospectively applicable procedure for registering thoracic studies from different modalities in a short amount of time and with minimal operator intervention. METHODS: CT and PET studies were acquired from six patients. The pleural surfaces in both image sets were determined by segmenting based on 50% of the maximum soft-tissue value in the study. These surfaces were converted into three-dimensional volumes and used to register the CT and PET studies in three dimensions using a sum of least squares fitting approach. The registered PET study was then displayed in a hot metal scale overlayed on top of the gray scale CT study. The accuracy of the fit was evaluated through a phantom study and preliminary clinical evaluation. RESULTS: A phantom study was performed to determine the limits of this technique. The accuracy was determined to be less than 2.3 mm in the x and y direction and 3 mm in the z direction. Preliminary clinical evaluation was also performed with encouraging results. CONCLUSION: This technique accurately registers PET and CT images of the thorax, retrospectively, without the need for external fiducial markers or other a priori action.

Aged↗

PubMed1994

Evaluation of emission-transmission registration in thoracic PET.

UNLABELLED: The intent of this investigation was to quantitate the amount of misregistration between PET emission and transmission scans of the thorax that occurs in a normal clinical environment. METHODS: The data from 17 FDG myocardial studies were evaluated. Prior to injection, a transmission study was acquired for 15 min using a 68Ge/68Ga ring source. The location of the cross-hairs from a laser alignment system was marked on the patient who was then removed from the scanner and injected with 10 mCi of FDG. After 45 min, the patient was placed back on the table and repositioned with the previously placed marks and a 15-min emission scan was acquired. The outline of the lungs on both the transmission and emission images was manually segmented. Both attenuation-corrected and noncorrected emission images were evaluated and the one that provided clearer visualization of the outline of the lungs was chosen for segmentation. The segmented contours of the transmission and emission scans were then registered with the method described by Pelizzari et al. using the transmission image as the "head" and the emission image as the "hat." The allowable transformations were x and y shifts and rotation in the transverse plane. RESULTS: Shifts in the x-axis averaged 2.4 mm (range: 0.2-7.3 mm, 80% less than 3.3 mm) with shifts in the y-axis averaging 2.6 mm (range: 0.1-8.7 mm, 80% less than 2.4 mm) and rotations in the transverse plane averaging 1.6 degrees (range: 0.2 to 5.1 degrees, 80% less than 2.4 degrees). A phantom study indicated that the accuracy of this method of evaluating misregistration was 2.35 mm and 1.81 mm in the x and y directions, respectively. CONCLUSION: Our preliminary evaluation indicates that careful application of laser alignment is an adequate method of registration in most cases.

Algorithms↗

PubMed1992

Biphasic solid and liquid gastric emptying in normal controls and diabetics using continuous acquisition in LAO view.

The purpose of this study was to investigate the various phases of gastric emptying using a dual-isotope liquid-solid meal ([99mTc]SC egg sandwich and [111In]DPTA in water) and continuous acquisition in the left anterior oblique view. The study groups consisted of 10 normal controls and 20 diabetics with symptoms suggestive of diabetic gastroparesis. Solid-phase emptying in both groups almost always had a lag phase followed by linear emptying. Liquid-phase emptying was biexponential in 4/10 normals and 12/20 diabetics, with a short early rapid emptying rate (mean T1/2 = 48 min in normals and 79 min in diabetics). Solid emptying was delayed in 10, normal in eight, and rapid in two diabetics. Liquid emptying was delayed in 9/10 diabetics who had delayed solid emptying. Diabetics as a group had a significantly delayed solid lag phase (P less than 0.025), rate of emptying (P less than 0.05) and percent emptying at 90 min (P less than 0.025) compared to normal controls. Diabetic liquid emptying was also significantly delayed (P less than 0.025). The second component of liquid emptying strongly correlated with the solid rate of emptying (r = 0.826 in normals and 0.855 in diabetics). Continuous acquisition of gastric emptying studies in the LAO view has allowed us to better define the various phases of solid and liquid gastric emptying.

Adolescent↗

PubMed1992

Sensitivity, resolution and image quality with a multi-head SPECT camera.

This investigation sought to determine which collimation factors were most important in providing superior image quality with a three-headed SPECT device. The relationship between sensitivity, resolution and SPECT image quality was studied. Two different sets of parallel-hole collimators were used. The ultrahigh-resolution collimators have higher spatial resolution (8.9 versus 11.0 mm), but only 55% of the sensitivity of the high-resolution collimators. A phantom with hot rods was imaged with both collimator sets. Observers compared images with the ultrahigh-resolution collimators to images of varying counts with the high-resolution collimators and determined which high-resolution images matched the ultrahigh-resolution images in image quality. Eleven patient studies were acquired with both collimator sets for equal time, and observers chose which image set they preferred. Transverse images of brain and liver studies were simulated with varying resolution and counts and subjectively compared. The phantom study indicated that the improvement in resolution led to image quality comparable to increasing the number of counts by a factor of 2.5 to 3.4. The clinical studies showed that the ultrahigh-resolution collimators were preferred in a large majority of the cases. These trends were also seen in the simulation study. These results confirm that higher resolution collimators should be used with multihead SPECT devices. The improvement in resolution more than compensates for the loss in sensitivity, leading to an overall improvement in image quality.

Brain↗

PubMed1992

Calculation of a gallbladder ejection fraction: advantage of continuous sincalide infusion over the three-minute infusion method.

The purpose of this study was to investigate alternative methods of infusing sincalide for calculation of a gallbladder ejection fraction (GBEF) during cholescintigraphy (5 mCi 99mTc-mebrofenin). After gallbladder filling, three methods of infusion were compared in 23 normal volunteers: (1) 0.02 microgram/kg as a 3-min infusion, (2) 0.02 microgram/kg as a 30-min infusion, and (3) 0.01 microgram/kg as a 30-min infusion (14 subjects), all performed on separate days. With the 3-min infusion, the emptying pattern was usually exponential and completed in 15 min. The mean (GBEF) was 52% +/- 26% at 20 min and 56% +/- 27% at 30 min (range 0%-100%). GBEFs were less than 35% in six subjects and 35%-38% in four. Side effects were noted by 11/23 subjects. With the slow infusions, emptying was linear; no side effects were noted. With 0.02 microgram/kg, the mean GBEF was 50% +/- 27% at 20 min and 70% +/- 22% at 30 min (range 26%-95%). Similar results were seen with 0.01 microgram/kg, but the data were more limited. The 30-min infusion had a higher normalcy rate than the 3-min method (91% versus 74%). Females had significantly lower GBEFs than males (p less than 0.05%). We conclude that the slow infusion method is preferable; it is more physiological, results in more complete emptying, has no side effects, has less normal variability, and should improve the specificity of this test. The lower mean female GBEF may have pathophysiological significance.

Adult↗

PubMed1991

Improved detection of small cavernous hemangiomas of the liver with high-resolution three-headed SPECT.

The purpose of this study was to review our experience with 99mTc-red blood cell scintigraphy for diagnosis of cavernous hemangiomas of the liver using a new three-headed, high-resolution dedicated SPECT system. Of 19 patients referred with a total of 38 lesions seen on CT, US, or MRI, 14 patients had 24 lesions that were hemangioma-positive with SPECT (all true-positives). Six of these 14 patients also had 9 hemangioma-negative lesions; all were less than or equal to 1.3 cm in size and false-negative. The remaining five patients had hemangioma-negative lesions only (1 false-negative, 4 true-negatives). Two hemangiomas were seen by SPECT that were not detected by CT, US, or MR. The sensitivity for hemangiomas greater than or equal to 1.4 cm. was 100% (20/20). The sensitivity was 33% for lesions 0.9-1.3 cm, and 20% for lesions less than or equal to 0.8 cm. The smallest hemangioma detected was 0.5 cm. These results show a definite improvement in sensitivity with high-resolution triple-headed SPECT over previously reported results using single-headed SPECT. High-resolution SPECT has improved our ability to detect small cavernous hemangiomas of the liver.

Erythrocytes↗

PubMed1991

Three-dimensional SPECT simulations of a complex three-dimensional mathematical brain model and measurements of the three-dimensional physical brain phantom.

We have developed a three-dimensional computer simulation of SPECT imaging. We have applied the simulation procedure to the realistic mathematical Hoffman three-dimensional brain model to generate the projection data (in the absence of attenuation, scatter, or noise) of both a parallel-hole and a multidetector SPECT system with point-focusing collimators. The simulated projection data were then reconstructed using standard software. The projection data resulting from the distribution of grey matter alone, or grey and white matter, were simulated. The results of these simulations indicate the existence of significant qualitative and quantitative artifacts in reconstructed human brain images. For example, the reconstructed values for grey matter along a cortical circumferential profile in a transverse slice through the basal ganglia varied by a factor of 2.40 (parallel-hole) and 2.99 (point-focusing), although the original grey matter values were identical in all cortical regions in the model. We have compared the simulated reconstructed images with those obtained by imaging the physical three-dimensional Hoffman brain phantom, which was constructed based upon the same set of data from which the mathematical three-dimensional Hoffman brain model was derived. Although the simulation did not include all of the degrading factors present in the physical imaging, the two images were in good agreement, indicating the applicability of the simulation to a realistic situation and the importance of the detector resolution effect.

Artifacts↗

PubMed1989

Left anterior oblique projection and peak-to-scatter ratio for attenuation compensation of gastric emptying studies.

Compensation for soft-tissue attenuation is necessary for accurate quantitation of nuclear gastric emptying studies. We sought an attenuation compensation method that would require the acquisition of images from a single projection, thus allowing for continuous dynamic acquisition. We investigated the use of the left anterior oblique (LAO) projection and the peak-to-scatter ratio (P/S) method. Phantom studies indicated that the P/S was not only a function of the amount of overlying attenuating material but also a function of the activity in the small intestine. Two models for the P/S method were developed, one that considered the activity in the small intestine and one that did not. A series of 27 patients (21 for solid gastric emptying and six for liquid gastric emptying) were studied comparing the results using the geometric mean (GM) method with the two P/S methods, the LAO and the uncorrected anterior (ANT) projection. The uncorrected ANT view for solid gastric emptying underestimated the percent emptying at 60 min by approximately 7%. The P/S method did not adequately compensate for attenuation. The use of the LAO projection yielded results that were highly correlated and unbiased when compared to the GM method. Accurate estimates of liquid gastric emptying can be obtained without attenuation compensation.

Drinking↗

PubMed1988

The effect of the Garren-Edwards Gastric Bubble on solid and liquid gastric emptying.

To determine the effect of the Garren-Edwards Gastric Bubble (GEGB) on gastric emptying, radionuclide solid and liquid gastric emptying in 12 obese patients prior to insertion of the GEGB was studied. Four were restudied at one and seven days and ten patients were restudied at twelve weeks with the GEGB in place. There were no significant differences in liquid gastric emptying at one and seven days nor in solid and liquid gastric emptying at twelve weeks. Solid gastric emptying was significantly decreased from a mean of 63% to 31% after one day (P less than 0.05) and returned to preplacement baseline by seven days. These results indicate that gastric emptying is not significantly changed after twelve weeks with the GEGB in place. Therefore, the mechanism of action for weight reduction with the GEGB is not likely to be mediated by an effect on gastric emptying. However, the solid food-induced dyspeptic symptoms commonly noted 1-3 days after placement of the GEGB, which resolve within seven days, are probably explained by transiently delayed solid gastric emptying.

Adolescent↗

PubMed1988

Comparison of bone mineral density in both hips.

Dual-photon absorptiometry (DPA) was performed on both hips of 40 patients to determine if the calculated bone-mineral density (BMD) of one hip could be used to predict the BMD of the opposite hip. For the Ward triangle, femoral neck, and greater trochanter the correlation coefficients between the BMD of the two hips was .920, .917, and .843, and the standard errors (SE) of the estimate for the linear regression of the left hip on to the right were 0.067, 0.063, and 0.077 g cm-2. The absolute error of predicting one hip from the other was not a function of BMD and thus the relative error increases with lower BMD values. The relative errors were 17%, 8%, and 7% for BMDs of 0.4, 0.8, and 1.0 g cm-2, respectively. The interobserver variability was small, with an r value of .96 and an SE of the estimate value of 0.036 g cm-2. The relative error in the mild-to-moderate osteoporosis categories was 2.5 times the precision of the instrument, indicating that the asymmetry of BMD is due to real differences between hips. Therefore the BMD of one hip cannot be used to predict that of the other with sufficient accuracy to discriminate clinically relevant trends in BMD.

Adult↗

PubMed1988

Renal scans in pregnant transplant patients.

This study demonstrates the normal technetium-99m diethylenetriaminepentaacetic acid ([99mTc]DTPA) renal scan in pregnant patients with transplanted kidneys. Five pregnant renal transplant patients had seven [99mTc]DTPA renal studies to assess allograft perfusion and function. All scans showed the uteroplacental complex. The bladder was always compressed and distorted. The transplanted kidney was frequently rotated to a more vertical position. In all patients allograft flow and function were maintained. There was calyceal retention on all studies and ureteral retention activity in three of five patients. Using the MIRD formalism, the total radiation absorbed dose to the fetus was calculated to be 271 mrad. This radiation exposure is well within NRCP limits for the fetus of radiation workers and an acceptable low risk in the management of these high risk obstetric patients.

Female↗

PubMed1988

Characterization of the rotating display.

The rotating display is a useful method for reviewing single photon emission computed tomography (SPECT) data. This study evaluated the requirements for a subjectively pleasing and useful implementation of this technique. Twelve SPECT data sets were modified and viewed by several observers who recorded the minimum framing rates for apparent smooth rotation, 3D effect, effects of image size, and other parameters. The results showed that a minimum of 16 frames was needed for a useful display. Smaller image sizes and more frames were preferred. The recommended minimal framing rate for a 64-frame study is 16-17 frames per second and for a 32-frame study, 12-13 frames per second. Other enhancements also were useful.

Data Display↗

PubMed1987

99mTc-glucoheptonate for quantitation of differential renal function.

Differential renal function was calculated by using 99mTc-glucoheptonate (Tc-GH) in 51 patients. Computer-acquired background-corrected individual renal function was calculated by using both the 1-3-min uptake counts and the 2-4-hr delayed static counts. The degree of correlation between the two was high (r = .96). An equally high correlation was noted in 16 children who were 12 years old or younger, in 15 patients with renal size disparity greater than 60/40%, and in six patients with abnormal creatinine clearances. Ten patients had a 30-min dynamic 99mTc-DTPA study followed immediately by the injection of Tc-GH and acquisition of delayed static images 2-4 hr later. A high degree of correlation (r = .99) was seen between the 1-3-min differential function obtained by using Tc-DTPA and the 2-4-hr delayed differential function obtained by using Tc-GH. This study shows that Tc-GH is a clinically useful and valid tool for calculation of differential renal function and that Tc-GH combines many of the best aspects of Tc-DTPA and Tc-DMSA.

Adolescent↗

PubMed1987

Hepatic visualization on iodine-131 whole-body thyroid cancer scans.

This study examines the frequency and significance of diffuse liver uptake on 131I whole-body thyroid cancer scans. Sixty whole-body scans on 27 patients with differentiated thyroid cancer were reviewed. Liver uptake was quantitated on another 21 studies (16 patients). Diffuse hepatic uptake was seen in 44% of patients and 35% of all the studies. It correlated best with the 131I dose administered (r = 0.733) and the product of the 131I percent radioactive iodine uptake (RAIU) and administered dose (r = 0.656), less well with the serum 131I protein bound iodine (r = 0.494) and the RAIU. This study demonstrates that liver visualization is more common than generally appreciated and is related to the 131I dose and indices of thyroid function although other factors may also play a role in liver visualization.

Adenocarcinoma↗

PubMed1986

Impact of radiocontaminants in commercially available iodine-123: dosimetric evaluation.

Iodine-123 (123I) is considered by some to be the radionuclide of choice for thyroid scintigraphy because of its ideal physical and biological characteristics and low radiation absorbed dose to the thyroid. However, commercially available 123I (p,2n) and (p,5n) have radiocontaminants. The MIRD formalism was used to estimate the absorbed dose to the thyroid for various age groups receiving recommended administered activities at the time of delivery and at two half-lives assuming radiocontamination levels specified by the suppliers. The calculations demonstrate that an 131I uptake with a technetium-99m scan at the time of delivery results in less absorbed dose to the thyroid than an 123I (p,2n) scan and uptake. At two half-lives the absorbed dose triples and becomes equivalent to the dose from an 131I scan. The absorbed dose from an 123I (p,5n) scan at two half-lives is higher than that of an 123I (p,2n) scan at the time of delivery. Iodine-123 capsules should not be decayed down in order to obtain a recommended pediatric administered activity. There appears to be no dosimetric advantage of commercially available 123I for thyroid scintigraphy for adults or most children.

Adolescent↗

PubMed1985

Thallium/technetium functional imaging of the thyroid and parathyroid. A case report.

This case report demonstrates the usefulness and limitations of technetium/thallium scintigraphy in the diagnosis of parathyroid hyperplasia. In addition, discordant thyroid tracer uptake (Tc-99m but not TI-201) due to colloid cysts is described. Another perspective in the controversy over which radiopharmaceutical, Tc-99m or TI-201, should be injected first also is presented.

Aged↗