Three-dimensional printing facilitates surgical planning for resection of an atypical cardiac myxoma.

BACKGROUND: Cardiac myxomas are common and account for 50% of primary intracardiac tumors. Atypical locations of cardiac myxoma increase the risk of intraoperative iatrogenic injuries. Herein, we report a case of using three-dimensional printing (3D) to facilitate the removal of an atypical cardiac myxoma in a 63-year-old woman. METHODS AND RESULTS: Mass in the high posterior atrial septum was confirmed through imaging. Due to the potential involvement of the mass to surrounding vital structures, 3D printing of the cardiac mass was performed. The tumor was completely resected via median sternotomy and the resulting defect was repaired with the bovine pericardium. The patient had an uncomplicated postoperative course except for the development of sick sinus syndrome. One-year follow-up showed no tumor recurrent. CONCLUSION: 3D printing technology in patients with atypical cardiac tumors enhances our understanding of the extent of the tumor invasion and facilitates planning the operation to avoid intraoperative complications.

Three-Dimensional-Printed Model as a Template for Chest Wall Reconstruction.

BACKGROUND: To our knowledge, this is the first time that a three-dimensional (3D)-printed model was used as an intraoperative template to recreate the resected portion of the lateral chest wall after resection of a large chest-wall tumour. METHODS: Fabrication of 3D-printed models requires collaboration among a surgeon, radiologist, segmenter, and 3D printing centre. Three-dimensional models are created with computed tomographic and magnetic resonance data. These models can provide an accurate guide for surgical resection and can be used intraoperatively as a template to construct tailored prostheses. RESULTS: We achieved complete resection of the chest wall defect, restored skeletal function and physiologic chest excursion, and achieved the best cosmetic appearance in all cases. CONCLUSIONS: Small- to medium-sized chest wall defects can be repaired with musculocutaneous flaps with or without prosthetic materials, but more complicated defects require increasingly sophisticated reconstructive techniques and technologies. An advanced technique is the use of a 3D-printed model of the chest wall as an intraoperative template.

Safety and Image Quality of 1.5-T Endorectal Coil Multiparametric MRI of the Prostate or Prostatectomy Fossa for Patients With Pacemaker or Implantable Cardioverter-Defibrillator.

OBJECTIVE: The purpose of this study is to report the patient safety and image quality of 1.5-T multiparametric MRI of the prostate in patients with cardiac implantable electronic devices (CIEDs). MATERIALS AND METHODS: In this retrospective study, a database was searched to identify prostate multiparametric 1.5-T MRI examinations performed with endorectal coils for patients with CIEDs from 2012 to 2016 (study group) and matched patients without CIEDs (control group). Clinical safety in the study group was reviewed. The specific absorption rate (SAR) and signal-to-noise ratio (SNR) were measured in both groups. Imaging quality and artifact on T2-weighted images, DW images, and dynamic contrast-enhanced images were rated on a 5-point scale by two independent readers. RESULTS: The study group consisted of total 28 multiparametric MRI examinations in 25 patients. There were no serious device-related adverse effects observed (0/28; 0%), and the estimated whole-body SAR in the study group was never greater than 1.5 W/kg. The SNR values tended to be lower in the study group than in the control group. However, overall perceived image preferences and influences of artifacts on image quality for the study group were not significantly different from those for the control group (p > 0.05), which were rated above average (rating 3) by both readers 1 and 2. CONCLUSION: Multiparametric 1.5-T MRI examination of the prostate can be safely performed in selected patients with CIEDs under controlled conditions with applicable image quality while maintaining a SAR less than 1.5 W/kg.

Association Between Advances in High-Resolution Cross-Section Imaging Technologies and Increase in Prevalence of Pancreatic Cysts From 2005 to 2014.

BACKGROUND & AIMS: Increasingly, pancreatic cysts are discovered incidentally in patients undergoing cross-sectional imaging for nonpancreatic reasons. It is unclear whether this increase is caused by improved detection by progressively more sophisticated cross-sectional imaging techniques or by a true increase in prevalence. We aimed to determine the prevalence of incidental pancreatic cysts in patients undergoing magnetic resonance imaging (MRI) for nonpancreatic indications on successive, increasingly sophisticated MRI systems. Also, we compared prevalence based on the demographic characteristics of the patients. METHODS: We collected data from MRIs performed at the Mayo Clinic in Florida during the sample months of January and February, from 2005 to 2014. Each patient's clinical chart was reviewed in chronological order to include the first 50 MRIs of each year (500 total). Patients were excluded if they had pancreatic disease including cysts, pancreatic surgery, pancreatic symptoms, pancreatic indication for the imaging study, or previous abdominal MRIs. An expert pancreatic MRI radiologist reviewed each image, looking for incidental pancreatic cysts. RESULTS: Of the 500 patients analyzed, 208 patients (41.6%) were found to have an incidental cyst. A significant relationship was observed between pancreatic cysts and patient age (P < .0001), diabetes mellitus (P = .001), and nonpancreatic cancer (P = .01), specifically nonmelanoma skin cancer (P = .03) or hepatocellular carcinoma (P = .02). The multivariable model showed a strong association between hardware and software versions and detection of cysts (P < .0001); the old hardware detected pancreatic cysts in 30.3% of patients, whereas the newest hardware detected cysts in 56.3% of patients. CONCLUSIONS: Based on an analysis of data collected from 2005 through 2014, newer versions of MRI hardware and software corresponded with higher numbers of pancreatic cysts detected. Older age, diabetes, and the presence of nonpancreatic cancer (specifically nonmelanoma skin cancer and hepatocarcinoma) were also associated with the presence of cysts.

Motion artifacts in kidney stone imaging using single-source and dual-source dual-energy CT scanners: a phantom study.

PURPOSE: Dual-energy computed tomography (DECT) has shown the capability of differentiating uric acid (UA) from non-UA stones with 90-100% accuracy. With the invention of dual-source (DS) scanners, both low- and high-energy images are acquired simultaneously. However, DECT can also be performed by sequential acquisition of both images on single-source (SS) scanners. The objective of this study is to investigate the effects of motion artifacts on stone classification using both SS-DECT and DS-DECT. METHODS: 114 kidney stones of different types and sizes were imaged on both DS-DECT and SS-DECT scanners with tube voltages of 80 and 140 kVp with and without induced motion. Postprocessing was conducted to create material-specific images from corresponding low- and high-energy images. The dual-energy ratio (DER) and stone material were determined and compared among different scans. RESULTS: For the motionless scans, all stones were correctly classified with SS-DECT, while two cystine stones were misclassified with DS-DECT. When motion was induced, 94% of the stones were misclassified with SS-DECT versus 11% with DS-DECT (P < 0.0001). Stone size was not a factor in stone misclassification under motion. Stone type was not a factor in stone misclassification under motion with SS-DECT, although with DS-DECT, cystine showed higher number of stone misclassification. CONCLUSIONS: Motion artifacts could result in stone misclassification in DECT. This effect is more pronounced in SS-DECT versus DS-DECT, especially if stones of different types lie in close proximity to each other. Further, possible misinterpretation of the number of stones (i.e., missing one, or thinking that there are two) in DS-DECT could be a potentially significant problem.

Validation of frontal near-infrared spectroscopy as noninvasive bedside monitoring for regional cerebral blood flow in brain-injured patients.

OBJECT: Near-infrared spectroscopy (NIRS) offers noninvasive bedside measurement of direct regional cerebral arteriovenous (mixed) brain oxygenation. To validate the accuracy of this monitoring technique, the authors analyzed the statistical correlation of NIRS and CT perfusion with respect to regional cerebral blood flow (CBF) measurements. METHODS: The authors retrospectively reviewed all cases in which NIRS measurements were obtained at a single, academic neurointensive care unit from February 2008 to June 2011 in which CT perfusion was performed at the same time as NIRS data was collected. Regions of interest were obtained 2.5 cm below the NIRS bifrontal scalp probe on CT perfusion with an average volume between 2 and 4 ml, with mean CBF values used for purposes of analysis. Linear regression analysis was performed for NIRS and CBF values. RESULTS: The study included 8 patients (2 men, 6 women), 6 of whom suffered subarachnoid hemorrhage, 1 ischemic stroke, and 1 intracerebral hemorrhage and brain edema. Mean CBF measured by CT perfusion was 61 ml/100 g/min for the left side and 60 ml/100 g/min for the right side, while mean NIRS values were 75 on the right and 74 on the left. Linear regression analysis demonstrated a statistically significant probability value (p<0.0001) comparing NIRS frontal oximetry and CT perfusion-obtained CBF values. CONCLUSIONS: The authors demonstrated a linear correlation for frontal NIRS cerebral oxygenation measurements compared with regional CBF on CT perfusion imaging. Thus, frontal NIRS cerebral oxygenation measurement may serve as a useful, noninvasive, bedside intensive care unit monitoring tool to assess brain oxygenation in a direct manner.

New bone formation over dehiscent semicircular canal with cartilage cap.

PURPOSE: Cartilage cap resurfacing is a method to seal a superior semicircular canal dehiscence. The purpose of this study was to evaluate the detection of new bone formation after surgical placement of a cartilage cap over a dehiscent semicircular canal. METHODS: In this retrospective review, two neuroradiologists blinded to each other's interpretation reviewed the temporal bones of 20 patients, five of which had a pre-operative computed tomography (CT) exam which was interpreted as unilateral superior semicircular canal dehiscence and with new bone formation following repair on follow-up CT. There were also 15 control subjects. Each neuroradiologist was blinded to history, including post-operative changes, and asked to determine if there was a dehiscence or no dehiscence. RESULTS: Out of the 15 controls, there was 100% inter-observer agreement. On the five post-operative patients, there was agreement in 4/5 that there was no dehiscence post-operatively and 1/5 agreement of dehiscence post-operatively, but ectopic bone adjacent to the dehiscence. CONCLUSION: Our results indicate that new bone formation can be seen at the site of cartilage cap placement over the dehiscence and be interpreted as bony closure of the dehiscence.

Creation of an optic nerve sheath diameter ultrasound model for NeuroICU education.

BACKGROUND: Using ultrasound to measure optic nerve sheath diameter (ONSD) is an emerging bedside technique to noninvasively assess intracranial pressure (ICP) in patients with brain injury. This technique is unique among bedside ultrasonography and is often performed by providers who have no formal ultrasound training. We sought to create a low-cost, 3D, reusable ONSD model to train neurology, neurosurgery, and critical care providers in measuring ICP. RESULTS: We identified 253 articles, of which 15 were associated with models and 2 with simulation. One gelatin model was reported, upon which we based our initial design. We could not validate the visual findings of this model; however, after constructing multiple beta models, the design most representative of human eye anatomy was a globe made of ballistics gel and either a 3 mm, 5 mm, or 7 mm × 50 mm 3D-printed optic nerve inserted into a platform composed of ballistics gel, all of which sat inside a 3D-printed skull. This model was used to teach ONSD measurements with ultrasound at a continuing medical education event prior to training on a live human model. CONCLUSION: A simple 3D ballistic ONSD model allows learners to practice proper hand placement and pressure, basic landmarks, and ONSD measurement prior to operating on a human eye. This model is replicable and sustainable given that the globe and platform are composed of ballistics gel.

Magnetic resonance imaging compatibility of endoclips.

BACKGROUND: Endoscopic clipping devices are now available for treatment of GI hemorrhage and microperforations. All commercially available endoclips are labeled as magnetic resonance imaging (MRI) incompatible. No data are available about the actual magnetic field strength at which endoclips are first deflected nor the clinical relevance of the magnetic fields on endoclips used in GI endoscopy. OBJECTIVE: To determine the compatibility of different endoclips with MRI. DESIGN: Prospective observational study. SETTING: Experiment on excised pig tissue in an MRI scanner. INTERVENTIONS: The physical deflection and strength of attraction of endoclips: Resolution Clip, TriClip, QuickClip, and Ethicon Endo-surgery Clip were measured in different positions by using an MRI scanner at a field strength of 1.5 Tesla. Endoclips that demonstrated deflection were attached to a pig stomach and tested for detachment at a 1.5-Tesla MRI field strength. MAIN OUTCOME MEASUREMENTS: Physical deflection and detachment from pig stomach mucosa in an MRI scanner. RESULTS: All endoclips except the one made by Ethicon Endo-surgery demonstrated physical deflection under the tested conditions. The magnetic attraction was strongest for the Resolution Clip (0.7 gauss) compared with the TriClip (1.2 gauss) and the QuickClip (26.8 gauss). Only the Triclip demonstrated detachment from the pig gastric tissue under testing conditions. LIMITATIONS: A pig model and a small number of clips. CONCLUSIONS: The Ethicon Endo-surgery clip is compatible with MRI. All other clips showed deflection in a magnetic field, but only the TriClip demonstrated detachment from gastric tissue, and hence should be considered MRI incompatible.

MR imaging of brainstem atrophy in progressive supranuclear palsy.

BACKGROUND: To enhance the sensitivity and specificity of the clinical diagnosis of progressive supranuclear palsy (PSP), neuroradiological parameters established in pathologically proven cases are needed. METHODS: We examined brainstem atrophy in five pathologically confirmed PSP patients (three men, mean age at death 77 years, range 64-84 years). Time interval between symptom onset and MRI ranged from 1 to 5 years, and between MRI and death from 33 to 52 months. Only one patient had clinical diagnosis of PSP at the time of MRI. Control group consisted of 19 age- and gender-matched healthy subjects. Seventeen morphometric parameters of the midbrain and pons were measured on T1-weighted midsagittal and T2-weighted axial MRI scans with Image Analyzer. Measurements of superior cerebellar peduncle (SCP) width were performed on PSP autopsy specimens. RESULTS: Mean SCP width on MRI in PSP (2.7 +/- 0.8 mm, 95%CI: 2.1-3.3) was smaller than in controls (3.7 +/- 0.5 mm, 95%CI: 3.5-3.9). Mean SCP width at autopsy was 8% smaller than mean SCP width on MRI. Midsagittal midbrain area in PSP (99.1 +/- 6.9 mm(2), 95%CI: 90.5-107.6) was smaller than in controls (141.0 +/- 18.1 mm(2), 95%CI: 132.2-149.7). Midbrain/pons area ratio in PSP was 1:5 and in controls was 1:4 (p < 0.01). Repeat MRI 17 months later in one PSP case revealed 30% decrease of SCP width. CONCLUSIONS: MR imaging with quantitative analysis may be useful in the diagnosis of early PSP and in monitoring disease course.

Measurement of caval blood flow with MRI during respiratory maneuvers: implications for vascular contrast opacification on pulmonary CT angiographic studies.

OBJECTIVE: Transient interruption of the contrast bolus has been described as a physiologic artifact that can sometimes result in poor opacification of the pulmonary arteries on pulmonary CT angiographic studies. To better understand the mechanism underlying this artifact, we used velocity-encoded cine MRI to measure flow in the inferior vena cava (IVC) and superior vena cava (SVC) during respiratory maneuvers. SUBJECTS AND METHODS: Quantitative measurements of SVC and IVC flow per R-R interval were performed on 10 healthy volunteers (six men, four women; median age, 30 years; range, 25-55 years) with a retrospectively ECG-gated velocity-encoded gradient-echo cine sequence on a 1.5-T MRI unit with axial slices at the level of the diaphragm and just below the azygous vein confluence during free breathing, continuous inspiration, breath-hold at end inspiration, Valsalva maneuver, and breath-hold at end expiration. RESULTS: Median flow during free breathing was 38.9 mL in the SVC and 74.3 mL in the IVC, during continuous inspiration was 43.9 mL in the SVC and 113.7 mL in the IVC, during breath-hold at end inspiration was 31.0 mL in the SVC and 56.1 mL in the IVC, during a Valsalva maneuver was 28.9 mL in the SVC and 53.9 mL in the IVC, and during breath-hold at end expiration was 35.3 mL in the SVC and 61.2 mL in the IVC. CONCLUSION: MRI measurements showed a significant increase in caval flow during inspiration and a greater relative increase in blood flow in the IVC than in the SVC. For thoracic CT performed with IV contrast enhancement, deep inspiration before scanning leads to a large influx of IVC blood that does not contain contrast medium and dilutes the contrast bolus, causing poor vascular opacification. Avoiding initial inspiration before scanning is suggested as a way to limit the transient interruption of the contrast bolus artifact.

Clinical-pathologic study of biomarkers in FTDP-17 (PPND family with N279K tau mutation).

The objective of this clinical-pathologic study was to identify biomarkers for a pallidopontonigral degeneration (PPND) kindred of frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17) harboring the N279K tau mutation. Five affected subjects, one at-risk who later became symptomatic, and one at-risk asymptomatic mutation carrier, had abnormal (18)fluorodeoxyglucose PET demonstrating asymmetric temporal lobe hypometabolism. All except the asymptomatic mutation carrier had abnormal brain MRI. Parkinsonism, myoclonus, anosmia, insomnia, speech, and autonomic dysfunction were identified. Autopsy of six affected subjects showed frontotemporal degeneration with extensive tauopathy. Further studies of FTDP-17 patients are needed to replicate these findings.

The Capabilities and Limitations of Clinical Magnetic Resonance Imaging for Detecting Kidney Stones: A Retrospective Study.

The purpose of this work was to investigate the performance of currently available magnetic resonance imaging (MRI) for detecting kidney stones, compared to computed tomography (CT) results, and to determine the characteristics of successfully detected stones. Patients who had undergone both abdominal/pelvic CT and MRI exams within 30 days were studied. The images were reviewed by two expert radiologists blinded to the patients' respective radiological diagnoses. The study consisted of four steps: (1) reviewing the MRI images and determining whether any kidney stone(s) are identified; (2) reviewing the corresponding CT images and confirming whether kidney stones are identified; (3) reviewing the MRI images a second time, armed with the information from the corresponding CT, noting whether any kidney stones are positively identified that were previously missed; (4) for all stones MRI-confirmed on previous steps, the radiologist experts being asked to answer whether in retrospect, with knowledge of size and location on corresponding CT, these stones would be affirmed as confidently identified on MRI or not. In this best-case scenario involving knowledge of stones and their locations on concurrent CT, radiologist experts detected 19% of kidney stones on MRI, with stone size being a major factor for stone identification.

Detection of different kidney stone types: an ex vivo comparison of ultrashort echo time MRI to reference standard CT.

BACKGROUND AND PURPOSE: With the development of ultrashort echo time (UTE) sequences, it may now be possible to detect kidney stones by using magnetic resonance imaging (MRI). In this study, kidney stones of varying composition and sizes were imaged using both UTE MRI as well as the reference standard of computed tomography (CT), with different surrounding materials and scan setups. METHODS: One hundred and fourteen kidney stones were inserted into agarose and urine phantoms and imaged both on a dual-energy CT (DECT) scanner using a standard renal stone imaging protocol and on an MRI scanner using the UTE sequence with both head and body surface coils. A subset of the stones representing all composition types and sizes was then inserted into the collecting system of porcine kidneys and imaged in vitro with both CT and MRI. RESULTS: All of the stones were visible on both CT and MRI imaging. DECT was capable of differentiating between uric acid and nonuric acid stones. In MRI imaging, the choice of coil and large field of view (FOV) did not affect stone detection or image quality. The MRI images showed good visualization of the stones' shapes, and the stones' dimensions measured from MRI were in good agreement with the actual values (R(2)=0.886, 0.895, and 0.81 in the agarose phantom, urine phantom, and pig kidneys, respectively). The measured T2 relaxation times ranged from 4.2 to 7.5ms, but did not show significant differences among different stone composition types. CONCLUSIONS: UTE MRI compared favorably with the reference standard CT for imaging stones of different composition types and sizes using body surface coil and large FOV, which suggests potential usefulness of UTE MRI in imaging kidney stones in vivo.

AAPM/RSNA physics tutorial for residents: fundamental physics of MR imaging.

Learning the basic concepts required to understand magnetic resonance (MR) imaging is a straightforward process. Although the individual concepts are simple, there are many concepts to learn and retain simultaneously; this situation may give the illusion that learning the physics of MR imaging is complicated. It is important for the radiologist who interprets MR images to understand the methods used to create the images because image contrast specifically depends on how the image data were acquired. Initial concepts include formation of magnetic fields from electric currents in loops of wire, the resonance phenomenon, the hydrogen proton and its frequency of precession, and absorption of radiofrequency energy. These concepts can then be applied to learn about T1 and T2 relaxation and contrast and how the acquisition parameters of echo time and repetition time can be used to achieve these image contrasts. Basic pulse sequences include the spin-echo, multiecho spin-echo, turbo spin-echo, inversion-recovery, and gradient-recalled-echo sequences.

Magnetic resonance imaging and deep brain stimulation.

OBJECTIVE: To determine whether cranial magnetic resonance imaging (MRI) is associated with deep brain stimulation (DBS) lead displacement or program interference. METHODS: In vitro and in vivo studies were performed with the Itrel II implantable pulse generator (IPG) (Model 7424; Medtronic, Minneapolis, MN), Medtronic 3387 and 3389 leads, and a 1.5-T GE Horizon LX scanner (General Electric, Milwaukee, WI). In the in vivo study, two MRI volumetric data sets were compared for each of five patients undergoing staged, bilateral, DBS electrode placement in the thalamic or subthalamic nucleus. The data sets were acquired shortly after the initial implantation and during stereotactic planning for the second implantation (1-8 mo between acquisitions). An additional thalamotomy-treated patient was included as a control patient. Volumetric data were analyzed in a blinded manner, using AnalyzeAVW 3.0 software (Biomedical Imaging Resource, Mayo Clinic, Rochester, MN), to determine lead movement. In the in vitro study, the IPG and leads were positioned in the magnetic field in various configurations and were systematically assessed for movement. RESULTS: In vivo, the majority of measured deviations (88%) were within the standard error of measurement (1.4 mm). The maximal measured deviation was 3 mm (2% occurrence). Excellent tremor control with stimulation was demonstrated, which did not change after MRI. In vitro, the DBS leads demonstrated no deflection when introduced into the magnetic field. Similarly, no changes in IPG battery strength, lead impedance, or program settings were observed. CONCLUSION: MRI was not associated with significant DBS electrode movement or changes in clinical responses. Other IPG models and components and MRI scanners should be evaluated, to develop specific guidelines for MRI among individuals with implanted DBS systems.

Kidney stone imaging with 3D ultra-short echo time (UTE) magnetic resonance imaging. A phantom study.

Computed tomography (CT) is the current gold standard for imaging kidney stones, albeit at the cost of radiation exposure. Conventional magnetic resonance imaging (MRI) sequences are insensitive to detecting the stones because of their appearance as a signal void. With the development of 2D ultra-short echo-time (UTE) MRI sequences, it becomes possible to image kidney stones in vitro. In this work, we optimize and implement a modified 3D UTE MRI sequence for imaging kidney stones embedded in agarose phantoms mimicking the kidney tissue and in urine phantoms at 3.0T. The proposed technique is capable of imaging the stones with high spatial resolution in a short scan time.

SPECT-negative SIRPIDs: less aggressive neurointensive care?

INTRODUCTION: The management of EEG patterns in comatose intensive care unit patients remains poorly studied regarding whether aggressive management improves outcomes. We hypothesized that stimulus-induced rhythmic, periodic, or ictal discharges (SIRPIDs) could be classified as ictal and interictal using single-photon emission computerized tomographic (SPECT) imaging to help guide aggressive or deescalate anticonvulsant management. METHODS: We performed a retrospective review of all cases of ICU patients at a single center, tertiary care academic center for evidence of SIRPIDs with concomitant SPECT imaging over a one year period. RESULTS: From 2011 to 2012, we retrospectively identified 2 of 235 intensive care unit EEGs-completed patients (both 20 minutes and continuous EEG), who had SIRPIDs who subsequently underwent SPECT imaging. Both patients were female, one aged 63 years who had aneurysmal subarachnoid hemorrhage and large intraparenchymal hematoma and the other aged 67 years who sustained a cardiac arrest. Continuous EEG in both demonstrated stimulation-provoked SIRPIDs within 6 to 8 days of hospitalization. A SPECT scan using technetium-hexamethylporpyleneamineoxime (HMPAO) performed during stimulation induced SIRPIDs on EEG, followed by a SPECT scan without SIRPIDs on EEG. In both patients, regional cerebral hyperperfusion was not present between the two SPECT scans. The absence of hyperperfusion on either scan and subtracted SPECT imaging helped reduce aggressive anticonvulsant use, infusion of propofol, or additional antiepileptic drugs. CONCLUSIONS: Single-photon emission computerized tomographic scan-negative SIRPIDs may supplement the EEG and modify aggressive therapies, but larger outcome-based studies are needed.