Patient motion frequently occurs during coincidence imaging studies performed on hybrid PET/SPECT systems due to long acquisition times (30-50 min). The influence of patient motion on image quality and a motion correction method with hybrid PET/SPECT systems were investigated on a Picker AXIS dual head system. The evaluation was done using phantoms made of point, line and spherical sources filled with F-18 solution and inserted in a cylinder. Translations of 0.5 to 4.0 cm in the axial direction, and rotations from 5/spl deg/ to 30/spl deg/ at various times during the acquisition were applied. SNR, object contrast, FWHM and FWTM were calculated. Object deformation caused by motion was expressed as the ratio of the moments of inertia corresponding to the principal axes. The motion correction method applied is based on acquiring multiple fast scans and comparing them for motion. Scans prior to and after rotation and translation of the phantom were reconstructed separately, and combined using image registration. Changes in position of the phantom caused a decrease in contrast and resolution, as well as mispositioning and splitting of the sources. Motion in the axial direction splits the source in two parts that can appear several slices apart depending on the size of the motion. FWHM increased from 8.4 mm to 11.3 mm, and FWTM increased from 14.6 mm to 21.2 mm when 30/spl deg/ rotation was applied. The deformation of the spherical sources changed from 7% (no motion) up to 91% over the of motions applied in this study. Detection and correction of motion from coincidence data is a complex problem. Since motion at a given angular position of the camera can affect 20-40 projections, recording pre and post motion events in the same image. The proposed correction method successfully corrects for arbitrary motion, however further work is required to evaluate performance and quantitative accuracy with clinical data.

UNLABELLED Current dosimetric models of the brain and head lack the anatomic detail needed to provide the physical data necessary for suborgan brain dosimetry. During the last decade, several new radiopharmaceuticals have been introduced for brain imaging. The marked differences of these tracers in tissue specificity within the brain and their increasing use for diagnostic studies support the need for a more anthropomorphic model of the human brain and head for use in estimating regional absorbed dose within the brain and its adjacent structures. METHODS A new brain model has been developed that includes eight subregions: the caudate nuclei, the cerebellum, the cerebral cortex, the lateral ventricles, the lentiform nuclei, the thalami, the third ventricle and the white matter. This brain model is incorporated within a total revision of the head model presented in MIRD Pamphlet No. 5 Revised. Modifications include the addition of the eyes, the teeth, the mandible, an upper facial region, a neck region and the cerebrospinal fluid within both the cranial and spinal regions. RESULTS Absorbed fractions of energy for photon and electron sources located in 14 source regions within the new model were calculated using the EGS4 Monte Carlo radiation transport code for particles in the energy range 10 keV-4 MeV. These absorbed fractions were then used along with radionuclide decay data to generate S values for 24 radionuclides that are used in clinical or investigational studies of the brain, 12 radionuclides that localize within the cranium and spinal skeleton and 12 radionuclides that selectively localize in the thyroid gland. CONCLUSION A substantial revision to the dosimetric model of the adult head and brain originally published in MIRD Pamphlet No. 5 Revised is presented. This revision supports suborgan brain dosimetry for a variety of radiopharmaceuticals used in neuroimaging. Dose calculations for the neuroimaging agent 1231-tropane provide an example of the new model and yield mean brain doses that are consistent with published values. However, the absorbed dose to subregions within the brain such as the caudate and lentiform nuclei may exceed the average brain dose by a factor of up to 5.

Conventional partial orbit SPECT acquisition (90/spl deg/, 120/spl deg/ or 180/spl deg/ depending on number of camera heads) on multihead cameras enhance the problems caused by patient motion or change in organ position ("cardiac creep"), since the misplaced data are present at several intervals in the projection set. The authors investigated the effects of source motion and developed new image motion correction methods based on 360/spl deg/ acquisition of each detector on a three camera SPECT system. Experimental measurements with point sources and cardiac phantom were used to evaluate the influence of source motion on SPECT images. A point source phantom was rotated 5-30/spl deg/ CCW and moved axially 0.5-4.0 cm. A cardiac phantom was moved in laterally (0.5-4.0 cm) and in the axial direction (0.5-4.0 cm). Cross-correlation of images from different heads at the same angular position is used to detect and correct for motion. Two correction methods were investigated: (1) summation of complete 360/spl deg/ projection sets without correction, (2) time normalization of projection frames without motion to replace frames affected by motion. The first method corrects for small displacement of the source (<0.5 cm translation and <5/spl deg/ rotation). The second method significantly decreases degradation in image quality and can reduce or eliminate losses in accuracy of quantitative indices calculated from image data since uncorrupted data sets at each angular position are available and used for correction. The proposed method with 360/spl deg/ rotation successfully corrects for arbitrary motion (translations and/or rotations).

UNLABELLED This study evaluates the use of the 99mTc-DTPA aerosol lung clearance method to investigate radiation-induced lung changes in eight patients undergoing radiotherapy for lung or breast carcinoma. The sensitivity of the method was compared with chest radiography for detecting radiation-induced changes in the lung, regional alterations within (irradiated region) and outside (shielded region) the treatment ports, effect of irradiated lung volume, and dependence on time after radiotherapy. METHODS Serial DTPA lung clearance studies were performed before the first radiation treatment (baseline), then weekly during a 5- to 7-wk course, and up to 12 times post-therapy over periods of 56-574 days. The total activity deposited in the lungs for each study was approximately 150 microCi (approximately 5.6 MBq). DTPA clearance, expressed in terms of the biological half-time, t 1/2, was computed from the slopes of the least-squares fit regression lines of the time-activity curves for the first 10 min for irradiated and shielded lung regions. RESULTS Major findings include: (a) significant and early DTPA t 1/2 changes were observed in all patients during and after radiotherapy; (b) changes in DTPA t 1/2 values were observed in both irradiated and shielded lung regions in all patients suggesting a radiation-induced systemic reaction; (c) changes in DTPA t 1/2 values were correlated (p < 0.05) with the irradiated lung volumes; (d) significantly reduced DTPA t 1/2 values were observed in three patients who subsequently presented with clinical symptoms and/or radiographic changes consistent with radiation pneumonitis (t1/2 felt to 19% +/- 6% of baseline values, compared with 64% +/- 17% in the remaining patients [p < 0.01]); (e) the onset of decreased DTPA t 1/2 values in these three patients occurred 35-84 days before clinical symptoms and/or radiographic changes; and (f) DTPA t 1/2 tended to approach baseline values with time after radiotherapy, suggesting a long-term recovery in lung injury. CONCLUSION These observations show significant and early alterations in DTPA lung clearance during and after radiotherapy that may provide a sensitive assay to monitor changes in radiation-induced lung injury and may facilitate early therapeutic intervention.

The effect on chronic crack users of a 3 month detoxification programme on lung clearance of inhaled Tc-99(m)-diethylenetriamine pentaacetate (Tc-99(m)-DTPA) aerosol, spirometry and gas exchange was determined in a controlled in-patient clinical treatment setting. Imaging studies were carried out in eight chronic crack users (four crack-only and four crack plus tobacco) before and after the successful completion of the detoxification programme to measure the clearance of inhaled Tc-99(m)-DTPA from the lungs, an index of lung epithelial permeability. Tc-99(m)-DTPA lung clearance, expressed in terms of the biological half-time, T-1/2, was determined from the slopes of the least-squares fit regression lines of the respective time-activity plots. The mean (+/- S.D.) global T-1/2 values of the crack-only (75+/-39 min) and crack plus tobacco users (22+/-10 min) were significantly shorter (P < 0.02 and P < 0.001, respectively) than from the lungs of the non-smoking controls (124 +/- 29 min). This was consistent with increased lung epithelial permeability secondary to crack-related lung injury. The mean global T-1/2 value of the crack plus tobacco users was significantly shorter (P < 0.05) than that of the crack-only users. After detoxification, the abnormally rapid lung clearance became normal in two of the four crack-only users studied, improved in a third and remained unchanged in the fourth, a subject whose T-1/2 value was already normal initially. However, lung clearance improved in only one of the four crack plus tobacco users studied. Faster Tc-99(m)- DTPA clearance was the only impairment found in seven of the eight crack users, the eighth having restrictive lung disease. Crack-related lung injury, reflected by abnormally rapid Tc-99(m)-DTPA lung clearance, may be at least partially reversible after a 3 month period of abstinence from crack.

SPECT and associated imaging procedures were used in beagle dogs to (1) evaluate the uptake, distribution, and clearance properties of i.v.-injected 123I IMP (IMP) and 99mTc HMPAO (HMPAO) in the brain, lungs, liver, and kidneys; (2) quantify the acute effects (after 15 sec) of very low doses (0.5 or 1.0 mg/kg) cocaine on the kinetics and localization properties of IMP and HMPAO; and (3) evaluate comparative imaging properties of IMP and HMPAO for measuring regional cerebral blood flow (rCBF). Regional and global uptake and localization of IMP or HMPAO were evaluated in control studies using dynamic planar (0–30 min) and SPECT imaging (at 35 min). The regional distribution properties of IMP and HMPAO in the brain were estimated from regions of interest (ROIs) drawn around anatomic structures on MR slices and manually registered with corresponding SPECT slices. Cocaine significantly reduced the 30-min IMP uptake in the brain and lungs by ~15%, but only slightly changed HMPAO uptake in the brain and other organs. In the control studies, the respective uptakes of IMP in the brain and lungs were 9 and 39% greater (p < 0.01) than those of HMPAO. In control SPECT studies, the highest uptake of IMP was observed in the thalamus and progressively less activity was observed in the parietal lobe, frontal lobe, cerebellum, occipital lobe, and entire brain; activity in the olfactory bulb was lower than in all other regions. Cocaine reduced IMP uptake in the cerebellum (p < 0.01), occipital lobe (p < 0.01), and entire brain (p < 0.05). IMP uptake (cpm/pixel-mCi) in the different brain regions was 1.3 to 2.1 times greater than that of HMPAO (p < 0.001). HMPAO uptake was more homogeneous throughout the gray matter of the brain; no significant uptake differences were observed among flagged regions. Results indicate that single, acute doses of cocaine, 0.5 and 1.0 mg/kg, significantly altered the uptake and localization properties of IMP in the dog's brain, lungs, liver, and kidneys. Variations in regional uptake of IMP in the parietal, frontal, and occipital lobes, cerebellum, and thalamus were greater than with HMPAO.

UNLABELLED:During the last decade, several new radiopharmaceuticals have been introduced for brain imaging. The marked differences of these tracers in tissue specificity within the brain and their increasing use for diagnostic studies support the need for a more anthropomorphic model of the human brain and head. Brain and head models developed in the past have comprised only simplistic representations of this anatomic region.METHODS:A new brain model has been developed which includes eight subregions: the caudate nucleus, the cerebellum, the cerebral cortex, the lateral ventricles, the lentiform nucleus, the thalamus, the third ventricle and the white matter. This brain model has been included within a slightly modified version of the head model developed by Poston et al. in 1984. The head model, which includes both the thyroid and eyes, was modified in this work to include the cerebrospinal fluid within the cranial and spinal regions.RESULTS:Absorbed fractions of energy for photon and electron sources located in thirteen source regions within the new head model were calculated using the EGS4 Monte Carlo radiation transport code for radiations in the energy range 10 keV to 4 MeV.CONCLUSION:S-values were calculated for five radionuclides used in brain imaging (11C, 15O, 18F, 99(m)Tc and 123I) and for three radionuclides showing selective uptake in the thyroid (99(m)Tc, 123I, and 131I). S-values were calculated using 100 discrete energy points in the beta-emission spectrum of the different radionuclides.

The comparative localization properties of 5 radiopharmaceuticals which have been used to image primary brain tumors were investigated in a transplanted gliosarcoma in the Fisher 344 rat. Planar and SPECT images using pinhole collimation were used to investigate localization 2-4 times between 13d and 28d after transplant Imaging studies of intravenously administered Tl-201 Cl, Tc-99m-HMPAO, -MIBI, and -DTPA, and I-123 IMT were made in 70 rats. Localization properties were measured in unirradiated (n=39) and irradiated (n=31, 22.5 Gy to brain, 14 days after transplant) control and tumor-bearing rats. Ex vivo imaging and well cup measurements were made at sacrifice. MRI was used to define tumor border ROIs. Major observations include: (1) Tl, IMT, DTPA, and MIBI show increased uptake in tumor, with tumor-to-nontumor uptake ratios (tnt) from planar pinhole ROIs ranging from 1.3{plus_minus}.1 to 2.9{plus_minus}.7 between 13 and 28 d after transplant; HMPAO shows decreased activity in tumor with tnt ranging from 0.4-0.6{plus_minus}.1; (2) high resolution SPECT provides significantly greater discrimination between tumor and nontumor uptake: SPECT tnt=10.3{plus_minus}2{sub DTPA}, 3.0{plus_minus}.3{sub IMT}, 10.5{plus_minus}2{sub MIBI}, 5.6{plus_minus}2{sub TL} and 0.4{plus_minus}.1{sub HMPAO}; planar tnt=2.2{plus_minus}.4{sub DTPA}, 1.4{plus_minus}.1{sub IMT}, 1.9{plus_minus}.4{sub MIBI}, 2.1{plus_minus}.7{sub TL}, and 0.5{plus_minus}.1{sub HMPAO}; and (3) no significant differences in uptake are seen betweenmore » irradiated, more slowly growing tumors and the unirradiated tumors, and maximum tnt contrast is observed at 21 d with all radiopharmaceuticals. The study shows Tc-99m DTPA and Tc-99m MIBI to have the highest selective uptake in irradiated and unirradiated growing tumor.« less

Background. High resolution spatial details of the distribution of activity in three dimensions is required to evaluate the localization and dosimetric properties of radiolabelled monoclonal antibodies in tumors and normal tissues. Planar imaging of small animals with a resolution of 5-10 mm is usually the imaging modality of choice. The authors investigated high resolution single-photon emission computed tomographic (SPECT) imaging, based on a rotating pinhole scintillation camera. Although the sensitivity of the pinhole collimator is low, several radionuclides offer suitable decay properties to perform pinhole SPECT, especially in conjunction with high activity levels used in radioimmunotherapy. Methods. Transverse, sagittal, and coronal sections were reconstructed using a three-dimensional cone-beam algorithm, which is a generalization of the two-dimensional fan-beam filtered backprojection algorithm. Before reconstruction, the pinhole projections were corrected for the decay of the radionuclide, geometric and intrinsic efficiency variations of the camera system, and center of rotation shift. Results. The spatial resolution at 50 mm from the pinhole collimator with 3.3 mm aperture was 3.4 mm, and the sensitivity 7.2 c/s/mu Ci for technetium-99m. With the 2 mm collimator the resolution was 2.2 mm, and the sensitivity was 2.6 c/s/mu Ci. To show the spatial resolution in vivo, a rat was injected with 185 MBq of technetium-99m-methylene diphosphonate or with 5 mCi technetium-99m-hexamethylpropylene amine oxime. The bone structures were well delineated in the methylene diphosphonate image, and in the hexamethylpropylene amine oxime image, the brain was nicely shown. For comparison a magnetic resonance image for the same section was done. Conclusions. High resolution SPECT imaging with the pinhole collimator provides mapping of the activity in three-dimensions, needed for more detailed biodistribution data and to perform more accurate dosimetry.

A study was conducted to evaluate the feasibility of simultaneous dual radionuclide brain imaging with 123I and 99mTc using photopeak image subtraction techniques or offset photopeak image acquisition. The contribution of the photons from one radionuclide to a second radionuclide's photopeak energy window (crosstalk) was evaluated for SPECT and planar imaging of a brain phantom containing 123I and 99mTc for a range of activity levels and distribution properties approximating those in rCBF images of the adult human brain. Crosstalk was evaluated for 10% symmetrical energy windows centered on the 123I and 99mTc photopeaks and for 10% energy windows asymmetrically placed to the left and right of the center of the respective photopeaks. Major observations include: (1) in the centered photopeak windows, 99mTc crosstalk in the 123I window is 8.9% of the 99mTc seen in the 99mTc window and ranges from 37.5% to 75.0% of the 123I in the 123I window. 123I crosstalk is 37.8% of the 123I seen in the 123I window and ranges from 4.4% to 8.9% of the 99mTc seen in the 99mTc window; (2) the spatial distribution of a radionuclide's crosstalk photons differs from that observed in the radionuclide's photopeak window; (3) a 99mTc photopeak window offset to the left does not decrease 123I crosstalk, and the percentage of 99mTc scattered photons is significantly increased in the window. Offsetting the 123I window to the right decreases 99mTc crosstalk to 9.0% to 17.9% of the 123I counts, but decreases 123I sensitivity by 39.9%; and (4) offsetting both photopeak windows to the right decreases the 99mTc scattered photons in the 99mTc window, but increases 123I crosstalk to 17.0% to 33.8% of the 99mTc counts. The findings show that image quality, spatial resolution, and quantitative accuracy are degraded to unacceptable levels with the combinations of energy windows tested for dual radionuclide imaging of 99mTc and 123I. This indicates that dual radionuclide imaging must be thoroughly tested and validated before use in clinical studies.

UNLABELLEDThe performance of pinhole SPECT and the application of this technology to investigate the localization properties of radiopharmaceuticals in vivo in small laboratory animals are presented.METHODSSystem sensitivity and spatial resolution measurements of a rotating scintillation camera system are made for a low-energy pinhole collimator equipped with 1.0-, 2.0- and 3.3-mm aperture pinhole inserts. The spatial detail offered by pinhole SPECT for in vivo imaging was investigated in studies of the brain and heart in Fisher 344 rats by administering 201TICI, 99mTc-HMPAO, 99mTc-DTPA and 99mTc-MIBI. Image acquisition is performed using a rotating scintillation camera equipped with a pinhole collimator; projection data are acquired in conventional step-and-shoot mode as the camera is rotated 360 degrees around the subject. Pinhole SPECT images are reconstructed using a modified cone-beam algorithm developed from a two-dimensional fanbeam filtered backprojection algorithm.RESULTSThe reconstructed transaxial resolution of 2.8 mm FWHM and system sensitivity of 0.086 c/s/kBq with the 2.0-mm pinhole collimator aperture provide excellent spatial detail and adequate sensitivity for imaging the regional uptake of the radiopharmaceuticals in tumor, organs and other tissues in small laboratory animals.CONCLUSIONThe resolution properties of pinhole SPECT are superior to those which have been achieved thus far with conventional SPECT or PET imaging technologies. Pinhole SPECT provides an important approach for investigating localization properties of radiopharmaceuticals in vivo.

Crosstalk components (XC) present in one or both energy windows (EWs) in dual radionuclide images can influence the detectability of cold defects and overestimate areas of hyperperfusion. Changes in lesion contrast due to the presence of crosstalk photons and correction methods were evaluated for combinations of radionuclides. Monte Carlo simulations of SPECT and planar imaging of a brain phantom containing 10 lesions ranging in size from 1 to 12 cm{sup 2} were run for Tc-99m, Xe-133, Tl-201 and I-123. Simulations of the gray and white matter compartments and lesions were run individually to allow greater flexibility in evaluating different radionuclide uptake distributions. Simulations of image acquisition at 15 EWs, corresponding to the baseline settings and EWs commonly used for imaging all four radionuclides, were recorded for each radionuclide. The system energy resolution (ER) was set at 1% intervals between 6 and 14%. XCs were calculated for: (1) Tc and I with 4:1 activity ratio (AR) of Tc/I; (2) Tc and Tl with a 5:1 AR and (3) Tc and Xe with a 2:1 and 4:1 AR. Cold defects of 10 to 60% with Xe, Tl and I were seen as 3 to 45% defects due to XC from Tc whenmore » similar distribution and defect size were assumed for both radionuclides. Large changes in lesion contrast were observed when multiple lesions with increased (hyperperfused regions) and decreased activity were used in the same study especially if cold lesions on Xe, Tl and I images, appear as regions with increased activity uptake on the Tc study. Image contrast improved when images recorded in the 100-110 keV EW were used to estimate and correct for Tc XC in the Xe- and Tl-studies; 10-60% defects were seen as defect of 6-55%. The study shows that large changes in lesion contrast and detectability due to XC can be corrected using a third EW in dual radionuclide imaging of Tc-Xe and Tc-Tl.« less

Sn-117m(4+)DTPA prepared at Brookhaven National Laboratory has favorable physical and biological characteristics for use as a palliative agent to relieve pain from osseous metastases. The short range of the emitted conversion electrons permits large bone radiation doses without excessive radiation to the bone marrow. An accompanying 158.6 keV gamma is useful for monitoring the distribution. The T1/2 of 13.6 days provides an adequate shelf life. A previous study in humans has demonstrated favorable dosimetry with a bone surface dose of approximately 57.9 mGy/MBq and a bone surface to marrow ratio of 10:1. This study was instituted to find a dose level which was effective and to monitor effects on bone marrow. Sn-117m was administered to 14 patients. Administered activity ranged between 66 and 573 MBq or 1.2-5.8 MBq/kg body weight. At the lower dose levels (<3.1 MBq/kg, n=7), 1 obtained good relief of pain, 1 partial relief, and 1 no relief. The remaining 4 were not evaluated because of the need for further treatment of soft tissue disease or because of intervening death. The 7 patients treated at the higher dose level (4.8-5.8 MBq/kg) included patients with prostate (3), breast (3) and unknown (1) primary cancers. All patients experienced reliefmore » of pain, 5 excellent and 2 partial. No marrow suppression was observed as a result of Sn-117m therapy. Initial observations indicate that Sn-117m DTPA is effective in palliation of pain from osseous metastases without producing bone marrow suppression. Further studies at a higher dose level are planned.« less

The uptake, distribution, and clearance properties of 123I-IMP in the brain were evaluated in controls and asymptomatic crack users to investigate cerebral blood flow alterations in crack abuse. Serial dynamic planar images of the brain (0-25 min), SPECT of the brain (0.5 hr and 4 hr) and whole-body scans (75 min) were obtained in 21 crack abusers and 21 control subjects. Major observations include: (a) foci of abnormally reduced 123I-IMP activity mainly in the frontal and parieto-occipital cortex or marked irregularities in the uptake of 123I-IMP throughout the cerebral cortex consistent with moderate to severe disruption in regional cerebral blood flow were observed on the 0.5 hr SPECT images of 16/21 asymptomatic crack users; (b) no correlation could be demonstrated between the incidence or severity of SPECT perfusion abnormality with the frequency, amount or length of time of crack use; (c) focal perfusion defects observed in 6/21 crack users on the 0.5-hr SPECT images partially or completely filled-in on delayed SPECT at 4 hr in four of six subjects; (d) the rate of cerebral uptake of 123I-IMP in crack users averaged 23% less than observed in control subjects over the first 25 min after tracer administration; and (e) 123I-IMP activity reaching the brain of cigarette smoking control subjects (n = 14) at 25 min after injection averaged 42.5% less than in nonsmoking controls (n = 7). Quantitative measurements of the uptake and distribution properties of 123I-IMP in the brain proved to be an objective, sensitive and useful measure of regional cerebral blood flow in crack abuse.

Tin-117 has certain physical characteristics (half-life of 13.6 days, low-energy-conversion electrons, gamma photon of 158.6 keV) that suggest that it may be a favorable agent for radionuclide therapy. It has been shown in animal models that Sn-117m in the chemical form Sn(4+)diethylenetriaminepentaacetic acid localizes selectively in bone. The authors therefore studied its whole-body distribution in 10 patients to obtain absorbed dose estimates for therapy. The results showed that more than 50% of the administered activity was absorbed in the bones of patients with metastatic carcinoma. Retention was determined primarily by radioactive decay. For adult men, the radiation absorbed dose estimate averaged 54.8 mGy/MBq (203 rad/mCi) to bone surfaces and 6.1 mGy/MBq (22.6 rad/mCi) to the red marrow. All other tissues received less than 1/10 of the dose received by red marrow. These results suggest that a clinical therapeutic trial should be attempted.

pharmaceutical. The patient inhales the aerosolized prod uctoveraperiodof3 mm.At thisflowrate,approximately 125 @tl of liquid is inhaled per minute. Most of the radio pharmaceutical is exhaled and trapped in a filter, and 3.1 @il/minare delivered to the alveoli. Following this initial phase, the patient breathes room air. The 99mTcDTPA that has been deposited in the alveoli crossesthe alveolar-capillarymembraneand entersthe