MR Imaging of the Cervical Spine in Nonaccidental Trauma: A Tertiary Institution Experience.

BACKGROUND AND PURPOSE: Cervical MR imaging has demonstrated a utility for detecting soft tissue injury in nonaccidental trauma. The purpose of this study was to identify the incidence and types of cervical spine injury on MR imaging in nonaccidental trauma and to correlate cervical spine injury with parenchymal injury on brain MR imaging and findings on head CT. MATERIALS AND METHODS: A retrospective review of children diagnosed with nonaccidental trauma in a tertiary referral pediatric hospital over 8 years was performed. Inclusion criteria were children younger than 5 years of age, a confirmed diagnosis of nonaccidental trauma, and cervical spine MR imaging within 1 week of presentation. Brain and cervical spine MR imaging, head CT, cervical radiographs, and skeletal surveys were reviewed. RESULTS: There were 89 patients included in this study (48 males; mean age, 9.1 months [range, 1-59 months]). Cervical spine injury on MR imaging was found in 61 patients (69%). Ligamentous injury was seen in 60 patients (67%), with interspinous ligaments being most commonly involved. Abnormal capsular fluid (atlanto-occipital and atlantoaxial) was present in 28 patients (32%). Cervical spine injury on MR imaging was significantly associated with parenchymal restricted diffusion on brain MR imaging and parenchymal injury on head CT (P = .0004 and P = .0104, respectively). Children with restricted diffusion on brain MR imaging were 6.22 (point estimate) times more likely to have cervical spine injury on MR imaging. CONCLUSIONS: There is a high incidence of cervical spine injury in pediatric nonaccidental trauma. Positive findings may affect management and suggest a traumatic etiology.

Pleomorphic xanthoastrocytoma of childhood: MR imaging and diffusion MR imaging features.

BACKGROUND AND PURPOSE: Pleomorphic xanthoastrocytomas are rare astrocytic neoplasms of childhood and young adulthood. The purpose of this retrospective review was to evaluate MR imaging features of pediatric pleomorphic xanthoastrocytomas with an emphasis on diffusion MR imaging. MATERIALS AND METHODS: Review of the neuro-oncology data base revealed 11 pediatric patients (range, 4.7-16.1 years) with pleomorphic xanthoastroacytomas with 9 of these patients having preoperative MR imaging available. Six patients had preoperative diffusion MR imaging. Demographics, histopathology slides, conventional imaging characteristics (location, cystic component, hemorrhage, enhancement, vasogenic edema, inner table scalloping), and ADC metrics (mean tumor ADC and tumor to normal brain ADC ratio) were evaluated. RESULTS: Three pleomorphic xanthoastrocytomas had anaplastic features. Ten tumors were supratentorial. Two-thirds (6 of 9) of all tumors were either predominantly cystic or had cystic components, and three-fourths (6 of 8) of the supratentorial tumors had associated inner table scalloping. Seven of the 9 tumors had marked vasogenic edema (>10 mm). Mean tumoral ADC (n = 7) was 912 ± 219 × 10(-6) mm(2)/s (min-max: 617-1189). The tumor to normal brain ADC ratio was 1.14 ± 0.26 (min-max: 0.75-1.47). CONCLUSIONS: Pleomorphic xanthoastrocytoma should be entertained in the differential diagnosis of peripheral supratentorial tumors that appear during childhood. Cysts, inner table scalloping, and marked vasogenic edema are relatively frequent features. Relatively low ADC values and ADC ratios are not uncommon in pleomorphic xanthoastrocytoma.

Diffusion MRI improves the accuracy of preoperative diagnosis of common pediatric cerebellar tumors among reviewers with different experience levels.

BACKGROUND AND PURPOSE: Although utility of diffusion MR imaging in the preoperative diagnosis of common pediatric cerebellar tumors is generally recognized, its added value has not been systematically studied previously. The purpose of this study was to evaluate the impact of diffusion MR imaging on the accuracy of preoperative diagnosis of common pediatric cerebellar tumors among reviewers with different experience levels. MATERIALS AND METHODS: Review of the neuro-oncology data base yielded 96 patients whose preoperative brain MR imaging included both diffusion MR imaging (b = 1000 s/mm(2)) and ADC maps. There were 38 pilocytic astrocytomas, 33 medulloblastomas, 17 ependymomas, and 8 atypical teratoid/rhabdoid tumors. Six reviewers (4 residents, 2 neuroradiologists) evaluated the examinations. Two sessions were conducted with each reviewer, without and with diffusion MR imaging data on 2 separate days. The impact of diffusion MR imaging on accuracy of diagnoses was assessed. RESULTS: In choosing the correct diagnosis of the 4 alternatives, performances of 5 of the 6 reviewers improved significantly with inclusion of the diffusion MR imaging data, from 63%-77% (P = .0003-.0233). The performance of 1 reviewer also improved, but the difference did not attain statistical significance (P = .1944). Inclusion of diffusion MR imaging data improved the likelihood of rendering a correct diagnosis (odds ratio = 3.16, 95% confidence interval = 2.07-4.00) over all tumor types. When embryonal tumors were regarded as a single group, the rate of correct diagnosis increased from 66%-83% with diffusion MR imaging data, and performances of all of the reviewers improved significantly (P = .0001-.05). The improvement in performances resulted from increased correct diagnoses of pilocytic astrocytomas, medulloblastomas, and atypical teratoid/rhabdoid tumors. There was no improvement in the correct diagnoses of ependymomas with inclusion of the diffusion MR imaging data. CONCLUSIONS: Diffusion MR imaging improves accuracy of preoperative diagnosis of common pediatric cerebellar tumors significantly among reviewers with differing experience levels.

Strengthening the argument for rapid brain MR imaging: estimation of reduction in lifetime attributable risk of developing fatal cancer in children with shunted hydrocephalus by instituting a rapid brain MR imaging protocol in lieu of Head CT.

BACKGROUND AND PURPOSE: Children with shunted hydrocephalus have been undergoing surveillance neuroimaging, generally in the form of head CT, for evaluation of ventricular size. As the life expectancy of these children has improved due to better shunt technology and medical care, risks related to the ionizing radiation incurred during multiple head CT examinations that they are expected to undergo throughout their lifetime have become a concern. The purpose of this study is to estimate the LAR of developing fatal cancer due to head CT for ventricular size assessment in children with shunted hydrocephalus and to assess the impact of instituting a rapid brain MR imaging protocol in reducing radiation exposure. MATERIALS AND METHODS: Retrospective review of medical records yielded 182 patients who underwent neuroimaging for assessment of ventricular size. Available neuroimaging studies (head CT and rapid brain MR) were counted and annual neuroimaging frequency was calculated. It was assumed that these patients undergo a similar number of neuroimaging studies annually through 20 years of age. A risk estimate was calculated based on the BEIR VII report and effective doses obtained using the International Commission on Radiologic Protection Report 103 organ weighting factors. RESULTS: The mean annual neuroimaging study frequency was 2.1. Based on the average age of 1.89 years, it was assumed neuroimaging surveillance commences in the second year of life. LAR was calculated assuming that a patient undergoes neuroimaging in the form of head CT at this frequency (2/year) through 20 years of age. Assuming 2 scans are performed per year and the low-dose head CT protocol is used, approximately 1 excess lifetime fatal cancer would be generated per 230 patients; with standard head CT, there would be 1 excess lifetime fatal cancer per 97 patients. CONCLUSIONS: Children with shunted hydrocephalus are at increased risk of developing fatal cancer if they are to undergo surveillance using head CT. Implementation of a rapid brain MR imaging protocol with no radiation detriment will reduce this risk.

Hyperlipidemia resulting in abnormal density and signal intensity of blood in a neonate with lipoprotein lipase deficiency.

We present the imaging findings in an 8-week-old infant with LPL deficiency. Due to markedly increased lipoproteins in the serum, abnormal hypodensity and abnormal T1-weighted hyperintensity were identified in the dural venous sinuses and medullary veins.

Subependymoma of the cerebellopontine angle and prepontine cistern in a 15-year-old adolescent boy.

SUMMARY: A case of cerebellopontine angle and prepontine cistern subependymoma in a 15-year-old adolescent boy is presented with a review of the literature. Apparent diffusion coefficient values for subependymoma are reported. Differential considerations for the unusual location of this rare tumor are discussed.

Sphenoid sinus craniopharyngioma simulating mucocele.

We present a case of extracranial craniopharyngioma simulating a sphenoid sinus mucocele in a 12-year-old female who presented with progressive subacute left-sided visual disturbance. Although infrasellar craniopharyngioma is a rare entity, the presence of foci of calcification within the lesion is a useful finding for diagnosis.

Monte Carlo evaluation of object shape effects in iodine-131 SPET tumor activity quantification.

In our clinical iodine-131 single-photon emission tomography (SPET) quantification for radioimmunotherapy, calibration and partial volume correction are based on measurements with phantoms containing spheres to simulate patient tumors even though real tumors are frequently nonspherical. In this study, Monte Carlo simulation was used to evaluate how object shape influences "spill-out" and "spill-in", which are major sources of quantification error associated with the poor spatial resolution of 131I SPET. Objects that varied in shape (spheres, cylinders, and an irregular structure) but were identical in activity and volume were simulated. Iterative reconstruction employed both attenuation and triple-energy-window scatter compensation. VOIs were defined in the reconstructed images both using physical boundaries and using expanded boundaries to allow for the limited resolution. When physical boundaries were used, both spill-out and spill-in were more significant for nonspherical structures than for spherical structures. Over the range of object volumes (50-200 ml) and at all background levels, VOI counts in cylinders were lower than VOI counts in spheres. This underestimation increased with decrease in object size (for the cold background -18% at 200 ml and -39% at 50 ml). It also decreased with increase in background activity because spill-in partially compensated for spill-out. It was shown that with a VOI larger than physical size, the results are independent of object shape and size only in the case of cold background. Activity quantification was carried out using a procedure similar to that used in our clinic. Quantification of nonspherical objects was improved by simple sphere-based partial volume correction, but the error was still large in some cases (for example, -39% for a 50-ml cylinder in a cold background and -35% for a 200-ml irregular structure defined on the basis of a typical tumor outlined on an X-ray computed tomography scan of a patient with non-Hodgkin's lymphoma). Partial volume correction by patient-specific Monte Carlo simulation may provide better quantification accuracy.

Accuracy of 131I tumor quantification in radioimmunotherapy using SPECT imaging with an ultra-high-energy collimator: Monte Carlo study.

UNLABELLED: Accuracy of 131I tumor quantification after radioimmunotherapy (RIT) was investigated for SPECT imaging with an ultra-high-energy (UHE) collimator designed for imaging 511-keV photons. METHODS: First, measurements and Monte Carlo simulations were carried out to compare the UHE collimator with a conventionally used, high-energy collimator. On the basis of this comparison, the UHE collimator was selected for this investigation, which was carried out by simulation of spherical tumors in a phantom. Reconstruction was by an expectation-maximization algorithm that included scatter and attenuation correction. Keeping the tumor activity constant, simulations were carried out to assess how volume-of-interest (VOI) counts vary with background activity, radius of rotation (ROR), tumor location, and size. The constant calibration factor for quantification was determined from VOI counts corresponding to a 3.63-cm-radius sphere of known activity. Tight VOIs corresponding to the physical size of the spheres or tumors were used. RESULTS: Use of the UHE collimator resulted in a large reduction in 131I penetration, which is especially significant in RIT where background uptake is high. With the UHE collimator, typical patient images showed an improvement in contrast. Considering the desired geometric events, sensitivity was reduced, but only by a factor of 1.6. Simulation results for a 3.63-cm-radius tumor showed that VOI counts vary with background, location, and ROR by less than 3.2%, 3%, and 5.3%, respectively. The variation with tumor size was more significant and was a function of the background. Good quantification accuracy (<6.5% error) was achieved when tumor size was the same as the sphere size used in the calibration, irrespective of the other parameters. For smaller tumors, activities were underestimated by up to -15% for the 2.88-cm-radius sphere, -23% for the 2.29-cm-radius sphere, and -47% for the 1.68-cm-radius sphere. CONCLUSION: Reasonable accuracy can be achieved for VOI quantification of 131I using SPECT with an UHE collimator and a constant calibration factor. Difference in tumor size relative to the size of the calibration sphere had the biggest effect on accuracy, and recovery coefficients are needed to improve quantification of small tumors.

Tumor-absorbed-dose estimates versus response in tositumomab therapy of previously untreated patients with follicular non-Hodgkin's lymphoma: preliminary report.

I-131-radiolabeled tositumomab (Anti-B1 Antibody), in conjunction with unlabeled tositumomab, was employed in a phase II clinical trial for the therapy of 76 previously-untreated follicular-non-Hodgkin's-lymphoma patients at the University of Michigan Cancer Center. For all patients, conjugate-view images were obtained at six to eight time points on seven consecutive days after a tracer infusion of the antibody. A SPECT image set was obtained on day two or three after the therapy infusion for 57 of the patients. Of these, 55 are suitable for dosimetric evaluation. To date, we have completed analysis and response characterization of 20 patients from the subset of 55. All 20 patients had either a complete response (CR) or a partial response (PR). Conjugate-views provided a time-activity curve for a composite of nearby, individual tumors. These tumors were unresolved in the anterior-posterior projection. Pre-therapy CT provided volume estimates. Therapy radiation dose was computed for the composite tumor by standard MIRD methods. Intra-therapy SPECT allowed the calculation of a separate dose estimate for each individual tumor associated with the composite tumor. Average dose estimates for each patient were also calculated. The 30 individual tumors in PR patients had a mean radiation dose of (369 +/- 54) cGy, while the 56 individual tumors in CR patients had a mean radiation dose of (720 +/- 80) cGy. According to a mixed ANOVA analysis, there was a trend toward a significant difference between the radiation dose absorbed by individual tumors for PR patients and that for CR patients. When the radiation dose depended on only the patient response, the p value was 0.04. When the radiation dose depended on the pre-therapy volume of the individual tumor as well as on the patient response, the p value was 0.06. Since the patient response was complete in 75% of the patients, the analysis of the total cohort of 55 evaluable patients is needed to have a larger number of PR patients to better test the trend toward a significant difference. A pseudo-prediction analysis for patient-level dose and response was also carried out. The positive predictive value and the negative predictive value were 73% and 80%, respectively when a patient's average radiation dose was used. The predictive values were 73% and 60%, respectively, when the patient's average base-10 logarithm of radiation dose was used. A complete overlap for the dose range of CR patients compared to that for PR patients precluded higher predictive values. In conclusion, there was a trend toward a significant difference in the radiation dose between CR and PR patients, but it was only moderately predictive of response.

Initial results for Hybrid SPECT--conjugate-view tumor dosimetry in 131I-anti-B1 antibody therapy of previously untreated patients with lymphoma.

UNLABELLED: A study of the use of 131I-labeled anti-B1 monoclonal antibody, proceeded by an unlabeled predose, for therapy of previously untreated non-Hodgkin's lymphoma patients has recently been completed at the University of Michigan, Ann Arbor. More than half of the patients treated were imaged intratherapy with SPECT to separate apparently large tumors, unresolved by conjugate views, into individual ones specified by CT scan. The dosimetry of these tumors is reported here. METHODS: The activity-quantification procedure used 3-dimensional CT-to-SPECT fusion so that attenuation maps could be computed from CT and that volumes of interest could be drawn on the CT slices and transferred to the SPECT images. Daily conjugate-view images after a tracer dose of labeled anti-B1 antibody followed by an unlabeled predose provided the shape of the time-activity curve for the calculation of therapy dosimetry. Reconstructed SPECT counts that were within a volume of interest were converted to activity by using a background-and-radius-adaptive conversion factor. Activities were increased for tumors less than 200 g using a recovery-coefficient factor derived from activity measurements for a set of spheres with volumes ranging from 1.6 to 200 cm3. The calculated tumor radiation absorbed dose was based, in part, on the CT volume and on the intratherapy-SPECT activity. RESULTS: The mean of the radiation dose values for 131 abdominal or pelvic tumors in 31 patients was 616 cGy with a standard deviation of +/- 50 cGy. The largest dose was 40 Gy and the smallest dose was 73 cGy. The mean volume for the tumors was 59.2 +/- 11.2 cm3. The correlation coefficient between absorbed dose and tumor volume was small (r2 = 0.007), and the slope of the least-squares fit represented a decrease of only 36.4 cGy per 100 cm3 increase in volume. This small slope may reflect a characteristic of anti-B1 antibody therapy that is important for its success. The mean absorbed dose per unit administered activity was 1.83 +/- 0.145 Gy/GBq. The largest value was 12.6 Gy/GBq, and the smallest value was 0.149 Gy/GBq. The mean dose for 9 axillary tumors in 5 patients was significantly lower than the average dose for abdominal and pelvic tumors (P = 0.01). Therefore, axillary tumors should be grouped separately in assessing dose-response relationships. Anecdotal patient results tended to verify the validity of using the shape of the conjugate-view time-activity curve for the average SPECT-intratherapy curve. However, there was also an indication that the shape varies somewhat for individual tumors with respect to time to peak. CONCLUSION: Hybrid SPECT-conjugate-view dosimetry provided radiation absorbed dose estimates for the individual patient tumors that were resolved by CT.

Trans-sphenoidal and sphenoethmoidal encephalocele: report of two cases and review of the literature.

Basal encephaloceles are the least common form of encephalocele. Due to the critical position of the bony defect, visual and endocrinological abnormalities are frequently associated with basal encephaloceles. There is significant confusion in the classification of basal encephaloceles, particularly among trans-sphenoidal, sphenoethmoidal and intrasphenoidal subtypes. Two cases of basal encephaloceles are presented (one trans-sphenoidal and one sphenoethmoidal), along with a review of the literature. The relationship between the basal encephaloceles and endocrinological abnormalities is also emphasized.

Characterization of scatter and penetration using Monte Carlo simulation in 131I imaging.

UNLABELLED: In 131I SPECT, image quality and quantification accuracy are degraded by object scatter as well as scatter and penetration in the collimator. The characterization of energy and spatial distributions of scatter and penetration performed in this study by Monte Carlo simulation will be useful for the development and evaluation of techniques that compensate for such events in 131I imaging. METHODS: First, to test the accuracy of the Monte Carlo model, simulated and measured data were compared for both a point source and a phantom. Next, simulations to investigate scatter and penetration were performed for four geometries: point source in air, point source in a water-filled cylinder, hot sphere in a cylinder filled with nonradioactive water, and hot sphere in a cylinder filled with radioactive water. Energy spectra were separated according to order of scatter, type of interaction, and gamma-ray emission energy. A preliminary evaluation of the triple-energy window (TEW) scatter correction method was performed. RESULTS: The accuracy of the Monte Carlo model was verified by the good agreement between measured and simulated energy spectra and radial point spread functions. For a point source in air, simulations show that 73% of events in the photopeak window had either scattered in or penetrated the collimator, indicating the significance of collimator interactions. For a point source in a water-filled phantom, the separated energy spectra showed that a 20% photopeak window can be used to eliminate events that scatter more than two times in the phantom. For the hot sphere phantoms, it was shown that in the photopeak region the spectrum shape of penetration events is very similar to that of primary (no scatter and no penetration) events. For the hot sphere regions of interest, the percentage difference between true scatter counts and the TEW estimate of scatter counts was <12%. CONCLUSION: In 131I SPECT, object scatter as well as collimator scatter and penetration are significant. The TEW method provides a reasonable correction for scatter, but the similarity between the 364-keV primary and penetration energy spectra makes it difficult to compensate for these penetration events using techniques that are based on spectral analysis.

Mycotic pseudoaneurysm of the aortic arch: an unusual complication of invasive pulmonary aspergillosis.

Invasive pulmonary aspergillosis (IPA) is usually a condition of the immunocompromised patients. The organism has a tendency to invade pulmonary blood vessels. Extension of a pulmonary parenchymal lesion to involve the mediastinal great vessels is very rare. This is the first case where the extension of IPA to the aortic arch and the formation of a pseudoaneurysm were demonstrated on serial CT scans.

I-131 anti-B1 therapy/tracer uptake ratio using a new procedure for fusion of tracer images to computed tomography images.

In patients with non-Hodgkin's lymphoma being treated by I-131-radiolabeled anti-B1 monoclonal antibody, we test the hypothesis that the activity taken up in tumors during therapy is the same as that observed during tracer evaluation, except for scaling by the ratio of administered activities. Chemotherapy-relapsed patients are imaged only with planar conjugate views, whereas previously untreated patients are imaged with planar conjugate views and with single-photon emission computed tomography (SPECT). The SPECT tracer activity quantification requires computed tomography (CT) to SPECT image fusion, for which we devised a new procedure: first, the tracer SPECT images are fused to the therapy SPECT images. Then, that transformation is combined with the therapy SPECT-to-CT transformation. We also use (a) the same volumes of interest defined on CT for both tracer and therapy image sets, and (b) a SPECT counts-to-activity conversion factor that adapts to background and rotation radius. We define R as the ratio of therapy activity percentage of infused dose over tracer activity percentage of infused dose at 2-3 days after monoclonal antibody infusion. For 31 chemotherapy-relapsed patients, the R ratio for 60 solitary or composite tumors averages 0.931 +/- 0.031. The hypothesis of R being 1 is rejected with greater than 95% confidence. However, the difference from 1 is only 7.4%. The range of R is 0.43-1.55. For seven previously untreated patients, R averages 1.050 +/- 0.050 for 24 solitary tumors evaluated by SPECT. For six of these patients, R averages 0.946 +/- 0.098 for one of these solitary tumors and for five composite tumors, evaluated by conjugate views. Both results agree with the hypothesis that R is 1. The range of R for the SPECT tumors is 0.71 +/- 0.03 to 1.82 +/- 0.53, and for the conjugate view tumors, it is 0.70-1.35. Plots of R versus tumor volume yield small correlation coefficients. That from SPECT approaches a statistically significant difference from zero correlation (P = 0.06). In summary, on average, the tumor percentage of infused dose following tracer administration is predictive of therapeutic percentage of infused dose within 8%. For greater accuracy with individual tumors, however, an intratherapy evaluation is probably necessary because the range of R is large.

MIRD pamphlet no. 16: Techniques for quantitative radiopharmaceutical biodistribution data acquisition and analysis for use in human radiation dose estimates.

This report describes recommended techniques for radiopharmaceutical biodistribution data acquisition and analysis in human subjects to estimate radiation absorbed dose using the Medical Internal Radiation Dose (MIRD) schema. The document has been prepared in a format to address two audiences: individuals with a primary interest in designing clinical trials who are not experts in dosimetry and individuals with extensive experience with dosimetry-based protocols and calculational methodology. For the first group, the general concepts involved in biodistribution data acquisition are presented, with guidance provided for the number of measurements (data points) required. For those with expertise in dosimetry, highlighted sections, examples and appendices have been included to provide calculational details, as well as references, for the techniques involved. This document is intended also to serve as a guide for the investigator in choosing the appropriate methodologies when acquiring and preparing product data for review by national regulatory agencies. The emphasis is on planar imaging techniques commonly available in most nuclear medicine departments and laboratories. The measurement of the biodistribution of radiopharmaceuticals is an important aspect in calculating absorbed dose from internally deposited radionuclides. Three phases are presented: data collection, data analysis and data processing. In the first phase, data collection, the identification of source regions, the determination of their appropriate temporal sampling and the acquisition of data are discussed. In the second phase, quantitative measurement techniques involving imaging by planar scintillation camera, SPECT and PET for the calculation of activity in source regions as a function of time are discussed. In addition, nonimaging measurement techniques, including external radiation monitoring, tissue-sample counting (blood and biopsy) and excreta counting are also considered. The third phase, data processing, involves curve-fitting techniques to integrate the source time-activity curves (determining the area under these curves). For some applications, compartmental modeling procedures may be used. Last, appendices are included that provide a table of symbols and definitions, a checklist for study protocol design, example formats for quantitative imaging protocols, temporal sampling error analysis techniques and selected calculational examples. The utilization of the presented approach should aid in the standardization of protocol design for collecting kinetic data and in the calculation of absorbed dose estimates.

MR imaging in a desmoid tumor of the posterior mediastinum with extension into the abdominal cavity. A case report.

We report on a rare case of desmoid tumor in a 40-year-old man with low back pain and cough. There was no history of previous surgery or trauma. MR imaging revealed a posterior mediastinal mass extending into the abdominal cavity.

Deadtime correction for two multihead Anger cameras in 131I dual-energy-window-acquisition mode.

Two side-by-side energy windows, one at the photopeak and one at lower energy, are sometimes employed in quantitative SPECT studies. We measured the count-rate losses at moderately high activities of 131I for two multihead Anger cameras in such a dual-window-acquisition mode by imaging a decaying source composed of two hot spheres within a warm cylinder successively over a total of 23 days. The window locations were kept fixed and the paralyzable model was assumed. In addition, for the Picker Prism 3000 XP camera, the source was viewed from three different angles separated by 120 degrees and the final results are from an average over these three angles. For the Picker camera, the fits to the data from the individual windows are good (the mean of the squared correlation coefficient equals 0.98) while for the Siemens Multispect camera fits to the data from head 1 and from the lower-energy, monitor window are relatively poor. Therefore, with the Siemens camera the data from the two windows are combined for deadtime computation. Repeated autopeaking might improve the fits. At the maximum count rate, corresponding to a total activity of 740 MBq (20 mCi) in the phantom, the multiplicative deadtime correction factor is considerably larger for the Picker than for the Siemens camera. For the Picker camera, it is 1.11, 1.12, and 1.12 for heads 1-3 with the photopeak window and 1.10 for all heads with the lower-energy monitor window. For the Siemens camera, the combined-window deadtime correction factor is 1.02 for head 1 and 1.03 for head 2. Differences between the deadtime correction factor for focal activity and for the total activity do not support the hypothesis of count misplacement between foci of activity at these count rates. Therefore, the total-image dead time correction is recommended for any and all parts of the image.

Preliminary results from intensity-based CT-SPECT fusion in I-131 anti-B1 monoclonal-antibody therapy of lymphoma.

BACKGROUND: In treatment of non-Hodgkin's lymphoma patients with predose-plus-I-131-labeled anti-B1 (anti-CD20) monoclonal antibody, an intratherapy single photon emission computed tomography (SPECT) image is an important part of research estimates of tumor dosimetry. For that imaging, a computed tomography (CT)-SPECT fusion is used both to obtain an attenuation map for the space-alternating generalized expectation maximization reconstruction and to provide CT-based volumes of interest (VoI) to determine activity in tumors and organs. Fusion based on external, skin-surface markers has been used but may not correctly superimpose internal structures. METHODS: A new algorithm, developed and implemented in the Department of Radiology, University of Michigan, and based on the mutual information of grayscale values, was investigated. Results from four anti-B1 therapy patients are presented. RESULTS: In one patient, the new intensity-based fusion provided total reconstructed counts for kidneys that were higher than those produced by marker-based fusion; therefore, the VoI was probably located more accurately. In a second patient, after an acquisition that did not include any skin markers, the new algorithm produced counts/pixel that were similar for four of five tumors consistent with what is expected from an ideal therapy combined with accurate count density estimates. The fifth tumor was quite small and will have its final activity estimate moved toward consistency with the others after a recovery coefficient multiplication. For four tumors in two patients, direct comparison of the two algorithms yielded count totals that were different by no more than 7.2%. CONCLUSIONS: The use of CT-SPECT fusion and subsequent transfer of tumor VoI originally drawn in high-resolution CT space offers potential advantages for quantifying tumor uptake of radioactivity. A new, mutual-information-based fusion algorithm is usable without skin markers. Results indicate that the new fusion algorithm gives equal tumor count values within 7.2% compared with fusion based on external markers. It increases estimates of kidney activity by an average of 6.4%.