Gender differences in performance of script analysis by older adults.

Script analysis as a test of executive functions is presumed sensitive to cognitive changes seen with increasing age. Two studies evaluated if gender differences exist in performance on scripts for familiar and unfamiliar tasks in groups of cognitively intact older adults. In Study 1, 26 older adults completed male and female stereotypical scripts. Results were not significant but a tendency was present, with genders making fewer impossible errors on the gender-typical script. Such an interaction was also noted in Study 2, which contrasted 50 older with 50 younger adults on three scripts, including a script with neutral familiarity. The pattern of significant interactions for errors suggested the need to use scripts that are based upon tasks that are equally familiar to both genders.

Comparison of MRI pulse sequences in defining prostate volume after permanent implantation.

PURPOSE: To determine the relative value of three MRI pulse sequences in defining the prostate volume after permanent implantation. METHODS AND MATERIALS: A total of 45 patients who received a permanent 125I implant were studied. Two weeks after implantation, an axial CT scan (2 mm thickness) and T1-weighted, T1-weighted fat saturation, and T2-weighted axial MRI (3-mm) studies were obtained. The prostate volumes were compared with the initial ultrasound planning volumes, and subsequently the CT, T1-weighted, and T1-weighted fat saturation MRI volumes were compared with the T2-weighted volumes. Discrepancies in volume were evaluated by visual inspection of the registered axial images and the registration of axial volumes on the sagittal T2-weighted volumes. In a limited set of patients, pre- and postimplant CT and T2-weighted MRI studies were available for comparison to determine whether prostate volume changes after implant were dependent on the imaging modality. RESULTS: T1-weighted and T1-weighted fat saturation MRI and CT prostate volumes were consistently larger than the T2-weighted MRI prostate volumes, with a volume on average 1.33 (SD 0.24) times the T2-weighted volume. This discrepancy was due to the superiority of T2-weighted MRI for prostate definition at the following critical interfaces: membranous urethra, apex, and anterior base-bladder and posterior base-seminal vesicle interfaces. The differences in prostate definition in the anterior base region suggest that the commonly reported underdose may be due to overestimation of the prostate in this region by CT. The consistent difference in volumes suggests that the degree of swelling observed after implantation is in part a function of the imaging modality. In patients with pre- and postimplant CT and T2-weighted MRI images, swelling on the T2-weighted images was 1.1 times baseline and on CT was 1.3 times baseline, confirming the imaging modality dependence of prostate swelling. CONCLUSION: Postimplant T2-weighted MRI images provided superior prostate definition in all critical regions of the prostate compared with CT and the other MRI sequences tested. In addition to defining an optimal technique, these findings call two prior observations into question. Under dosing at the anterior base region may be overestimated because of poor definition of the prostate-bladder muscle interface. The swelling observed after implantation was lower on T2-weighted images as well, suggesting that a fraction of postimplant swelling is a function of the imaging modality. These findings have implications for preimplant planning and postimplant evaluation. As implant planning techniques become more conformal, and registration methods become more efficient, T2-weighted MRI after implantation will improve the accuracy of postimplant dosimetry.

A performance comparison of flat-panel imager-based MV and kV cone-beam CT.

The use of cone-beam computed tomography (CBCT) has been proposed for guiding the delivery of radiation therapy, and investigators have examined the use of both kilovoltage (kV) and megavoltage (MV) x-ray beams in the development of such CBCT systems. In this paper, the inherent contrast and signal-to-noise ratio (SNR) performance for a variety of existing and hypothetical detectors for CBCT are investigated analytically as a function of imaging dose and object size. Theoretical predictions are compared to the results of experimental investigations employing largearea flat-panel imagers (FPIs) at kV and MV energies. Measurements were performed on two different FPI-based CBCT systems: a bench-top prototype incorporating an FPI and kV x-ray source (100 kVp x rays), and a system incorporating an FPI mounted on the gantry of a medical linear accelerator (6 MV x rays). The SNR in volume reconstructions was measured as a function of dose and found to agree reasonably with theoretical predictions. These results confirm the theoretically predicted advantages of employing kV energy x rays in imaging soft-tissue structures found in the human body. While MV CBCT may provide a valuable means of correcting 3D setup errors and may offer an advantage in terms of simplicity of mechanical integration with a linear accelerator (e.g., implementation in place of a portal imager), kV CBCT offers significant performance advantages in terms of image contrast and SNR per unit dose for visualization of soft-tissue structures. The relatively poor SNR performance at MV energies is primarily a result of the low x-ray quantum efficiencies (approximately a few percent or less) that are currently achieved with FPIs at high energies. Furthermore, kV CBCT with an FPI offers the potential of combined volumetric and radiographic/fluoroscopic imaging using the same device.

Characterization of a fluoroscopic imaging system for kV and MV radiography.

An on-line kilovoltage (kV) imaging system has been implemented on a medical linear accelerator to verify radiotherapy field placement. A kV x-ray tube is mounted on the accelerator at 90 degrees to the megavoltage (MV) source and shares the same isocenter. Nearly identical CCD-based fluoroscopic imagers are mounted opposite the two x-ray sources. These systems are being used in a clinical study of patient setup error that examines the advantage of kV imaging for on-line localization. In the investigation reported here, the imaging performance of the kV and MV systems are characterized to provide support to the conclusions of the studies of setup error. A spatial-frequency-dependent linear systems model is used to predict the detective quantum efficiencies (DQEs) of the two systems. Each is divided into a series of gain and spreading stages. The parameters of each stage are either measured or obtained from the literature. The model predicts the system gain to within 7% of the measured gain for the MV system and to within 10% for the kV system. The systems' noise power spectra (NPSs) and modulation transfer functions (MTFs) are measured to construct the measured DQEs. X-ray fluences are calculated using modeled polyenergetic spectra. Measured DQEs agree well with those predicted by the model. The model reveals that the MV system is well optimized, and is x-ray quantum noise limited at low spatial frequencies. The kV system is suboptimal, but for purposes of patient positioning yields images superior to those produced by the MV system. This is attributed to the kV system's higher DQE and to the inherently higher contrasts present at kV energies.

A radiographic and tomographic imaging system integrated into a medical linear accelerator for localization of bone and soft-tissue targets.

PURPOSE: Dose escalation in conformal radiation therapy requires accurate field placement. Electronic portal imaging devices are used to verify field placement but are limited by the low subject contrast of bony anatomy at megavoltage (MV) energies, the large imaging dose, and the small size of the radiation fields. In this article, we describe the in-house modification of a medical linear accelerator to provide radiographic and tomographic localization of bone and soft-tissue targets in the reference frame of the accelerator. This system separates the verification of beam delivery (machine settings, field shaping) from patient and target localization. MATERIALS AND METHODS: A kilovoltage (kV) x-ray source is mounted on the drum assembly of an Elekta SL-20 medical linear accelerator, maintaining the same isocenter as the treatment beam with the central axis at 90 degrees to the treatment beam axis. The x-ray tube is powered by a high-frequency generator and can be retracted to the drum-face. Two CCD-based fluoroscopic imaging systems are mounted on the accelerator to collect MV and kV radiographic images. The system is also capable of cone-beam tomographic imaging at both MV and kV energies. The gain stages of the two imaging systems have been modeled to assess imaging performance. The contrast-resolution of the kV and MV systems was measured using a contrast-detail (C-D) phantom. The dosimetric advantage of using the kV imaging system over the MV system for the detection of bone-like objects is quantified for a specific imaging geometry using a C-D phantom. Accurate guidance of the treatment beam requires registration of the imaging and treatment coordinate systems. The mechanical characteristics of the treatment and imaging gantries are examined to determine a localizing precision assuming an unambiguous object. MV and kV radiographs of patients receiving radiation therapy are acquired to demonstrate the radiographic performance of the system. The tomographic performance is demonstrated on phantoms using both the MV and the kV imaging system, and the visibility of soft-tissue targets is assessed. RESULTS AND DISCUSSION: Characterization of the gains in the two systems demonstrates that the MV system is x-ray quantum noise-limited at very low spatial frequencies; this is not the case for the kV system. The estimates of gain used in the model are validated by measurements of the total gain in each system. Contrast-detail measurements demonstrate that the MV system is capable of detecting subject contrasts of less than 0.1% (at 6 and 18 MV). A comparison of the kV and MV contrast-detail performance indicates that equivalent bony object detection can be achieved with the kV system at significantly lower doses (factors of 40 and 90 lower than for 6 and 18 MV, respectively). The tomographic performance of the system is promising; soft-tissue visibility is demonstrated at relatively low imaging doses (3 cGy) using four laboratory rats. CONCLUSIONS: We have integrated a kV radiographic and tomographic imaging system with a medical linear accelerator to allow localization of bone and soft-tissue structures in the reference frame of the accelerator. Modeling and experiments have demonstrated the feasibility of acquiring high-quality radiographic and tomographic images at acceptable imaging doses. Full integration of the kV and MV imaging systems with the treatment machine will allow on-line radiographic and tomographic guidance of field placement.

Colonic volvulus in children: value of barium enema for diagnosis and treatment in 14 children.

OBJECTIVE: Colonic volvulus is a rare type of intestinal obstruction in children. We reviewed our experience in 14 cases to determine the specific portion of the colon involved and the value of barium enema for diagnosis. MATERIALS AND METHODS: We retrospectively reviewed medical and radiologic records of 14 cases of colonic volvulus in children at the Children's Hospital of St. Paul from 1955 to 1992. Both abdominal plain radiographs and barium studies were examined. The children were 3 months to 15 years old. RESULTS: Two cases involved the transverse colon, two were cecal, and 10 occurred in the sigmoid colon. Findings on barium enema indicated colonic volvulus in all 14 children. The barium enema also was successful therapy in 11 of the 14 cases. CONCLUSION: As unusual as colonic volvulus is in children, it should remain in the differential diagnosis of abdominal pain of sudden onset in this age group. Fourteen cases were detected at our institution alone, two of which involved the transverse colon. The barium enema can be used to confirm the diagnosis and frequently is therapeutic.

A complete ileo-tumor-colic fistula in a child with Burkitt's lymphoma.

A boy with abdominal Burkitt's lymphoma developed rectal bleeding, abdominal distension, pain, and fever three weeks after diagnosis. Imaging studies revealed a necrotic tumor mass allowing a fistulous pathway from the ileum to the proximal colon. A laparotomy was performed, with resection of the large necrotic tumor. The child recovered, and has had no further evidence of Burkitt's disease. The radiological evaluation performed in this case ensured proper medical management and surgical intervention during a life-threatening event. The possibility of bowel perforation as a complication of therapy for abdominal lymphoma must be recognized.

Spondylometaphyseal dysplasia, corner fracture type: a heritable condition associated with coxa vara.

The authors present the radiographic features of a previously incompletely delineated bone dysplasia, which they call spondylometaphyseal dysplasia, corner fracture type. This is a dominant heritable condition associated with short stature and developmental coxa vara. The progressive hip deformity usually causes significant disability requiring surgical correction. Developmental coxa vara, simulated corner fractures of long tubular bones, and vertebral body abnormalities result in a diagnostic constellation. Knowledge of these distinctive radiologic features allows accurate diagnosis, which in turn should lead to appropriate genetic counseling and possibly to earlier, more efficacious surgical treatment of the coxa vara.

Doppler evaluation of renal transplants in children: a prospective analysis with histopathologic correlation.

Duplex Doppler sonography recently has been used to evaluate renal transplants. Some authors have stated that high resistive indexes (RIs) occur in the presence of acute renal transplant rejection. RIs less than 0.7 are considered as probably excluding acute transplant rejection. We performed a prospective study of duplex sonographic examinations of pediatric patients (mean age, 8 years; 13 boys, two girls) with renal allografts and clinically suspected transplant disease. The results of 22 duplex studies were correlated with histopathologic data obtained between July 1987 and June 1988. RIs of the arcuate arteries in patients with acute rejection (n = 14) averaged 0.62 (range, 0.50-0.80). The RI in patients with chronic rejection (n = 1) was 0.59. RIs in patients with acute tubular necrosis (n = 3) averaged 0.66 (range, 0.59-0.72). RIs in patients with cyclosporine A toxicity (n = 4) averaged 0.66 (range, 0.58-0.79). Tubulointerstitial rejection was predominant, with only two patients showing minimal acute vascular rejection. Thirteen of 14 pediatric patients with histologically proved renal transplant rejection had a resistive index of less than 0.70. This study refutes the concept that resistive indexes of less than 0.7 exclude acute rejection.

CT findings in left paraduodenal herniae.

Computed tomography (CT) was used to evaluate mass effect on the greater curvature of the stomach in two children with histories of intermittent, recurrent vomiting. The paraduodenal herniae were identified on CT in both of these patients as small bowel interposed between the stomach and the body of the pancreas.