Benjamin P. Liu

Computing oxygen-enhanced ventilation maps using correlation analysis

Correlation maps of oxygen‐enhanced ventilation were obtained in nine healthy volunteers using complete and selected image series. The complete series included all images acquired with the subjects alternately inhaling room air and 100% oxygen. The selected series were the subsets of the complete series and included only co‐registered images that showed matched diaphragmatic position at maximal expiration. Cross‐correlation was computed between the time response function of each pixel and the input function representing the alternation between periods of room air and 100% oxygen inhalation. The confidence level for the correlation analysis was set to 0.01. Pulmonary parenchymal anatomy was consistently reproduced throughout the lung, even in anterior slices where published data have reported correlation problems. The overall average correlation coefficient was 0.66 ± 0.07 for the complete series and 0.75 ± 0.08 for the selected series. It was concluded that correlation analysis could be used to reconstruct qualitative oxygen‐enhanced ventilation maps. Magn Reson Med 49:591–594, 2003.

Influence of oxygen flow rate on signal and T1 changes in oxygen-enhanced ventilation imaging

To investigate the optimal oxygen flow rate for oxygen‐enhanced MR ventilation imaging.

Ventilation‐perfusion ratio of signal intensity in human lung using oxygen‐enhanced and arterial spin labeling techniques

This study investigates the distribution of ventilation‐perfusion (V/Q) signal intensity (SI) ratios using oxygen‐enhanced and arterial spin labeling (ASL) techniques in the lungs of 10 healthy volunteers. Ventilation and perfusion images were simultaneously acquired using the flow‐sensitive alternating inversion recovery (FAIR) method as volunteers alternately inhaled room air and 100% oxygen. Images of the T1 distribution were calculated for five volunteers for both selective (T1f) and nonselective (T1) inversion. The average T1 was 1360 ms ± 116 ms, and the average T1f was 1012 ms ± 112 ms, yielding a difference that is statistically significant (P < 0.002). Excluding large pulmonary vessels, the average V/Q SI ratios were 0.355 ± 0.073 for the left lung and 0.371 ± 0.093 for the right lung, which are in agreement with the theoretical V/Q SI ratio. Plots of the V/Q SI ratio are similar to the logarithmic normal distribution obtained by multiple inert gas elimination techniques, with a range of ratios matching ventilation and perfusion. This MRI V/Q technique is completely noninvasive and does not involve ionized radiation. A limitation of this method is the nonsimultaneous acquisition of perfusion and ventilation data, with oxygen administered only for the ventilation data. Magn Reson Med 48:341–350, 2002.

Imaging in the evaluation of headache.

When deciding to perform imaging for headache, it is important to consider many factors including the pretest probability, prevalence of diseases, sensitivity of imaging, and implications for treatment. For the first presentation of a headache or a change in headache pattern, if the characteristics do not perfectly fit a primary headache type, imaging may be indicated according to the ICHD-2 criteria to exclude a secondary cause before a primary headache is diagnosed. The value of negative imaging should not be underestimated in the cost-benefit analysis, which often only takes into account number needed to treat or likelihood of finding a significant treatable abnormality. One study has shown that some groups of patients are less likely to overuse other parts of the health care system after negative neuroimaging. Further studies with stronger methodologies, finer differentiation of acute and chronic headache presentations, more advanced imaging technology, among other factors, can improve decision making on when to use imaging and assess the impact of imaging on patient satisfaction and quality of life. In addition, functional MRI, MRS, and voxel-based morphometry MRI are only some of the neuroimaging techniques currently used in research to further understand the pathophysiology and mechanisms of headache. In conclusion, although most headaches are a primary headache disorder with a benign course, imaging is an important part of the diagnostic evaluation to exclude the presence of a secondary cause of headache that could cause fatal results or severe neurologic morbidity. In headache patients without focal neurologic examination abnormalities, the yield of neuroimaging for significant intracranial findings is generally low. However, specific subgroups of headache patients and headache presentations can have much higher rates of significant intracranial abnormalities.

Labyrinthitis ossificans in a child with sickle cell disease: CT and MRI findings

The association between sensorineural hearing loss and sickle cell disease has been described, and labyrinthine hemorrhage has been reported with sickle cell disease. We report the CT and MRI findings of labyrinthitis ossificans in a child with sickle cell disease who presented with sensorineural hearing loss. Labyrinthitis ossificans is associated with an infectious, inflammatory, or destructive insult to the membranous labyrinth; however, it has not been specifically described with sickle cell disease. Recognition of this condition is important because it affects both management and prognosis of this disease.

Low-Dose Gamma Knife Radiosurgery for Vestibular Schwannomas: Tumor Control and Cranial Nerve Function Preservation After 11 Gy

Objectives This study aims to report tumor control rates and cranial nerve function after low dose (11.0 Gy) Gamma knife radiosurgery (GKRS) in patients with vestibular schwannomas. Methods A retrospective chart review was performed on 30 consecutive patients with vestibular schwannomas treated from March 2004 to August 2010 with GKRS at the Robert H. Lurie Comprehensive Cancer Center of Northwestern University. The marginal dose for all patients was 11.0 Gy prescribed to the 50% isodose line. Median follow‐up time was 42 months. The median treatment volume was 0.53 cm3. Hearing data were obtained from audiometry reports before and after radiosurgery. Results The actuarial progression free survival (PFS) based on freedom from surgery was 100% at 5 years. PFS based on freedom from persistent growth was 91% at 5 years. One patient experienced tumor progression requiring resection at 87 months. Serviceable hearing, defined as Gardner‐Robertson score of I‐II, was preserved in 50% of patients. On univariate and multivariate analyses, only higher mean and maximum dose to the cochlea significantly decreased the proportion of patients with serviceable hearing. Conclusion Vestibular schwannomas can be treated with low doses (11.0 Gy) of GKRS with good tumor control and cranial nerve preservation.

Posterior Glottic Stenosis with a Calcified Interarytenoid Scar Band: CT and Laryngoscopic Correlation

SUMMARY: A 52-year-old man with burn injuries and prolonged intubation developed PGS with hoarseness, dyspnea, and bilateral vocal cord immobility. On CT, a calcified interarytenoid scar band was identified, corresponding to an interarytenoid scar on laryngoscopy. Endoscopic laser lysis of the calcified scar band relieved the symptoms. We present laryngoscopic and CT findings of PGS with interarytenoid calcification along with the postlysis findings. The classification, clinical findings, imaging, and management of PGS are reviewed.

Superficial temporal artery pseudoaneurysm following craniotomy

We read with interest the letter by Lee et al describing a case of postoperative superficial temporal artery pseudoaneurysm.1 Although we agree that this complication is rare, we do not agree with their statement, “such a complication after cranial surgery has not previously been reported”. …

Radiation Exposure in Interventional Pain Management: We Still Have Much to Learn

Fluoroscopic-guided interventional pain management procedures have been increasingly performed in recent years, as they allow for enhanced target accuracy and improved patient safety. Clinical studies and review articles continue to be published that highlight the benefits and usefulness of performing these procedures under fluoroscopic guidance. However, the increased utilization of fluoroscopy has undoubtedly resulted in higher cumulative exposure of ionizing radiation for both the interventional pain management physicians and their patients. The primary source of ionizing radiation exposure during interventional pain procedures comes from scatter radiation that is reflected by the patient. Measures to reduce radiation to the physician include limiting the dose and time of exposure (increasing the distance between the physician and the X-ray tube, collimation, intermittent fluoroscopy, last image hold, pulsed fluoroscopy), and protection from the radiation (lead aprons, glasses, etc.). It is quite difficult to avoid scatter radiation in the interventional pain management procedure setting given the close proximity that the physician must maintain with the patient to perform the procedure. Most interventional procedures carried out for the management of chronic pain require short periods of fluoroscopy time. However, cumulative dose becomes of more concern if physicians routinely perform high volumes of interventional procedures including those procedures with higher fluoroscopy times such as spinal cord stimulator or intrathecal pump implantation and vertebral augmentation. It is well known that cumulative exposure to ionizing radiation is associated with significant adverse conditions including cancer, genetic defects, cataracts, dermatologic issues, and hematologic conditions. Despite these concerning effects, there remains a relative paucity of literature on ionizing radiation exposure and dose among interventional pain management physicians. Furthermore, minimal attention has been paid to the radiation-related effects on our patients, many of whom get numerous interventional pain procedures, ranging from simple to complex, per year, with no personal protective measures in place. The majority of published reports on this topic use fluoroscopic or screening times as a proxy for radiation dose (Table 1). While fluoroscopic times are easily measured, they may not necessarily be correlated to the radiation dose the patient or the physician is receiving and must not be viewed in isolation as a marker of exposure to radiation. Also, fluoroscopic times may vary by mode used (continuous vs. pulsed), the experience of the radiographer, technician, or interventionalist, or difficulties in obtaining a satisfactory image given the severity of degenerative disease or patient body habitus. In general, published data have shown that fluoroscopic times are longer in a university setting where supervision of trainees occurs, as compared to private practice. Even so, there is wide variation in fluoroscopy times and radiation dose in attending physicians in both private practice and university settings. Overweight patients also appear to require significantly longer fluoroscopy times and have higher radiation exposure compared to normal-weight patients. Some studies have reported radiation exposure through dosimetry measurements for a variety of interventional pain management procedures. These studies, which were performed in both private practice and university settings, have shown that radiation dose levels to interventional pain physicians are within regulated acceptable dose limits if appropriate radiation protection measures have been utilized (Table 2). Interpretation of these results has its limitations, as each study utilized different modes of fluoroscopy, varying types of shielding, and measured effective dose over differing lengths of time and at variable locations. Ultimately, DOI: 10.1111/papr.12290

The presence of a pituitary tumor in patients with prostate cancer is not a contraindication for leuprolide therapy

PurposeGonadotropin analogs like leuprolide play an important role in the management of prostate cancer. Pituitary apoplexy has been reported after leuprolide therapy. This report examines whether the presence of a pituitary tumor is a contraindication for leuprolide therapy in patients with prostate cancer.Materials and methodsTwo patients with prostate cancer and pituitary tumors were treated with leuprolide and radiation therapy. The first patient with a previously unknown pituitary adenoma had a leuprolide injection for prostate gland downsizing prior to brachytherapy. The second patient with a known pituitary microadenoma had a biochemical recurrence and was treated with leuprolide and radiation therapy.ResultsThe first patient developed symptoms of apoplexy a few hours after the leuprolide injection. He underwent a transsphenoidal resection of the sellar mass with complete neurologic recovery. The second patient did not have any adverse events after leuprolide with follow-up MRI scans showing no growth of the microadenomas.ConclusionThe presence of a pituitary tumor is not a contraindication for leuprolide therapy. While patients with a macroadenoma should have surgery first, those with a microadenoma may be considered for leuprolide therapy after careful evaluation by a multidisciplinary team.