Quantitative Comparison of Misregistration in Abdominal and Pelvic Organs Between PET/MRI and PET/CT: Effect of Mode of Acquisition and Type of Sequence on Different Organs.

OBJECTIVE: The objective of our study was to quantitatively compare misregistration in selected abdominopelvic organs between PET/CT acquisitions and simultaneous and sequential PET/MRI acquisitions. SUBJECTS AND METHODS: PET/MR images of 15 healthy volunteers and seven patients with bladder cancer were acquired. Ten clinical PET/CT studies acquired during the same time frame of body mass index-matched control subjects were chosen. PET/MRI and PET/CT registration of selected abdominopelvic organs was measured and compared. RESULTS: The overall mean misregistration with PET/MRI was significantly higher than that with PET/CT (p < 0.001). Sequential PET/MRI acquisition was significantly inferior to PET/CT (p = 0.02), whereas there was no significant difference between simultaneous PET/MRI acquisition and PET/CT (p = 0.38). Simultaneous PET/MRI acquisition was significantly better than sequential PET/MRI acquisition (p < 0.001). The mean misregistration for all organs with the T1-weighted volumetric interpolated breath-hold examination (VIBE) sequence (2.39 cm) was significantly inferior to PET/CT (p < 0.001). Although the T2-weighted HASTE breath-hold sequence was significantly inferior to PET/CT (p = 0.04), the T2 HASTE non-breath-hold sequence and T2 STIR sequence (0.18 cm) were significantly superior to both PET/CT and the T1 VIBE sequence (p < 0.001). Within the same sequence (T1 VIBE breath-hold sequence), the mean misregistrations with sequential and simultaneous PET/MRI acquisitions were both significantly greater than with PET/CT (p < 0.001), whereas simultaneous PET/MRI acquisition was superior to sequential PET/MRI acquisition (p < 0.001). CONCLUSION: In the abdominopelvic organs, sequentially obtained PET/MRI data have significantly higher misregistration than both PET/CT data and simultaneously acquired PET/MRI data. Simultaneously obtained PET/MRI data are statistically noninferior to PET/CT. Nonradial T1 VIBE has the highest misregistration, whereas T2 STIR and T2 HASTE non-breath-hold are significantly better than both PET/CT and T1 VIBE.

Normal pediatric prevertebral soft-tissue thickness on MDCT.

OBJECTIVE: The thickness of the prevertebral soft tissue (PVST) is instrumental in helping detect cervical spine injuries in the pediatric population. Current parameters for normal PVST thickness in that population are based on lateral radiographs because there have been no studies to date defining age-dependent normal measurements on MDCT. With the increasingly important role of MDCT in the evaluation of pediatric trauma patients, it is necessary to establish normal values for pediatric PVST thickness on MDCT images. Thus, the purpose of this study is to establish the normal thickness of PVST on MDCT of the pediatric population from 0 to 15 years old. MATERIALS AND METHODS: The thickness of the PVST was measured in 139 pediatric trauma patients (age range 0-15 years) who presented to the pediatric emergency department between 2005 and 2008. Patients included in the study were not intubated, had no congenital or acquired osseous abnormality detected on CT, and were discharged from the hospital without a diagnosis of cervical spine or soft-tissue injury. Exclusion criteria included patients with concurrent injury found on head CT or nontraumatic causes of PVST thickening, such as lymphadenopathy or retropharyngeal internal carotid arteries. Patients who were diagnosed with cervical injuries within 1 year after the initial CT examination were also excluded. Each patient was scanned with a cervical collar placing the cervical spine in a neutral or near-neutral position. RESULTS: The smallest variability and calculated SD were at C2 and C6. The upper limits of normal for PVST thickness at C2 were 7.6 mm in patients from 0 to 2 years old, 8.4 mm in patients from 3 to 6 years old, and 6.8 mm in patients from 7 to 10 years old and in those from 11 to 15 years old. At the C6 level, the upper limits were 9.0 mm in patients from 0 to 2 years old, 9.8 mm in patients from 3 to 6 years old, 12.1 mm in patients from 7 to 10 years old, and 14.5 mm in patients from 11 to 15 years old. The upper limit of normal had the highest variability at C3 and C4 for all age groups. CONCLUSION: The thickness of the PVST is important in the detection of underlying injuries to the cervical spine. MDCT is playing an increasingly important role in the evaluation of pediatric trauma patients. We propose the obtained values as the upper limits of normal for PVST thickness on MDCT images in the pediatric population from 0 to 15 years old.

Quantitative accuracy of positron emission tomography/magnetic resonance and positron emission tomography/computed tomography for cervical cancer.

With the spread of positron emission tomography/magnetic resonance (PET/MR), the question of comparability of studies becomes important. We aim to determine whether PET/MR and PET/computed tomography (PET/CT) are comparable for the case of cervical cancer. Fifteen cervical cancer patients identified by either a radiation oncologist or an oncologic surgeon had both PET/MR and PET/CT performed for initial staging within 3 weeks. We then compared the results both quantitatively (measuring standardized uptake values [SUVs] on visible lesions) as well as qualitatively (having radiologists and nuclear medicine physicians interprets the results). While interpretations between PET/MR and PET/CT varied in many cases, SUVs of primary lesions were similar to within 25% in all but one case, and correlation coefficient was 0.92. Maximum SUV ranged between 4.9 and 25.2 for PET-MR and between 5.8 and 30.4 for PET-CT for primary tumors and between 1.5 and 18.8 for PET-MR and between 1.8 and 20.8 for PET-CT for nodes. However, clinical reads often varied significantly between PET/MR and PET/CT. This suggests that SUV is similar on PET/MR and PET/CT although the differing anatomic modalities available for correlation may make the difference in terms of qualitative interpretation.

Ruptured intracranial dermoid cyst manifesting as new onset seizure: a case report.

Intracranial dermoid cysts are rare tumors derived from ectopic epithelial cells. They are slow-growing benign entities, but can cause significant morbidity through compression of neurovascular structures and, rarely, rupture into the subarachnoid space. We present a rare case of a spontaneously ruptured intracranial dermoid cyst presenting as new onset seizures due to chemical meningitis caused by dissemination of fat droplets.