Nadja A. Farshad-Amacker

Metal-induced artifacts in computed tomography and magnetic resonance imaging: comparison of a biodegradable magnesium alloy versus titanium and stainless steel controls

ObjectiveTo evaluate metal artifacts induced by biodegradable magnesium—a new class of degradable biomaterial that is beginning to enter the orthopedic routine—on CT and MRI compared to standard titanium and steel controls.MethodsDifferent pins made of titanium, stainless steel, and biodegradable magnesium alloys were scanned using a second-generation dual-energy multidetector CT and a 1.5-T MR scanner. In CT, quantitative assessment of artifacts was performed by two independent readers by measuring the noise in standardized regions of interest close to the pins. In MRI, the artifact diameter was measured. Interobserver agreement was evaluated using intraclass correlation coefficients. Artifacts were compared using Mann Whitney U tests.ResultsIn comparison to stainless steel, biodegradable magnesium alloys induced significantly fewer artifacts in both 1.5-T MRI (pu2009=u20090.019–0.021) and CT (pu2009=u20090.003–0.006). Compared to titanium, magnesium induced significantly less artifact-related noise in CT (pu2009=u20090.003–0.008). Although artifacts were less on MRI for biodegradable magnesium compared to titanium, this result was not statistically significant.ConclusionBiodegradable magnesium alloys induce substantially fewer artifacts in CT compared to standard titanium and stainless steel, and fewer artifacts in MRI for the comparison with stainless steel.

MR imaging of degenerative disc disease

Magnet resonance imaging (MRI) is the most commonly used imaging modality for diagnosis of degenerative disc disease (DDD). Lack of precise observations and documentation of aspects within the complex entity of DDD might partially be the cause of poor correlation of radiographic findings to clinical symptoms. This literature review summarizes the current knowledge on MRI in DDD and outlines the diagnostic limitations. The review further sensitizes the reader toward awareness of potentially untended aspects of DDD and the interaction of DDD and endplate changes. A summary of the available classifications for DDD is provided.

Effect of high-pitch dual-source CT to compensate motion artifacts: a phantom study.

RATIONALE AND OBJECTIVESnTo evaluate the potential of high-pitch, dual-source computed tomography (DSCT) for compensation of motion artifacts.nnnMATERIALS AND METHODSnMotion artifacts were created using a moving chest/cardiac phantom with integrated stents at different velocities (from 0 to 4-6 cm/s) parallel (z direction), transverse (x direction), and diagonal (x and z direction combined) to the scanning direction using standard-pitch (SP) (pitch = 1) and high-pitch (HP) (pitch = 3.2) 128-detector DSCT (Siemens, Healthcare, Forchheim, Germany). The scanning parameters were (SP/HP): tube voltage, 120 kV/120 kV; effective tube current time product, 300 mAs/500 mAs; and a pitch of 1/3.2. Motion artifacts were analyzed in terms of subjective image quality and object distortion. Image quality was rated by two blinded, independent observers using a 4-point scoring system (1, excellent; 2, good with minor object distortion or blurring; 3, diagnostically partially not acceptable; and 4, diagnostically not acceptable image quality). Object distortion was assessed by the measured changes of the objects outer diameter (x) and length (z) and a corresponding calculated distortion vector (d) (d = √(x(2) + z(2))).nnnRESULTSnThe interobserver agreement was excellent (k = 0.91). Image quality using SP was diagnostically not acceptable with any motion in x direction (scores 3 and 4), in contrast to HP DSCT where it remained diagnostic up to 2 cm/s (scores 1 and 2). For motion in the z direction only, image quality remained diagnostic for SP and HP DSCT (scores 1 and 2). Changes of the objects diameter (x), length (z), and distortion vectors (d) were significantly greater with SP (overall: x = 1.9 cm ± 1.7 cm, z = 0.6 cm ± 0.8 cm, and d = 1.4 cm ± 1.5 cm) compared to HP DSCT (overall: x = 0.1 cm ± 0.1 cm, z = 0.0 cm ± 0.1 cm, and d = 0.1 cm ± 0.1 cm; each P < .05).nnnCONCLUSIONnHigh-pitch DSCT significantly decreases motion artifacts in various directions and improves image quality.

Accuracy of patient-specific template-guided vs. free-hand fluoroscopically controlled pedicle screw placement in the thoracic and lumbar spine: a randomized cadaveric study

PurposeDorsal spinal instrumentation with pedicle screw constructs is considered the gold standard for numerous spinal pathologies. Screw misplacement is biomechanically disadvantageous and may create severe complications. The aim of this study was to assess the accuracy of patient-specific template-guided pedicle screw placement in the thoracic and lumbar spine compared to the free-hand technique with fluoroscopy.MethodsPatient-specific targeting guides were used for pedicle screw placement from Th2–L5 in three cadaveric specimens by three surgeons with different experience levels. Instrumentation for each side and level was randomized (template-guided vs. free-hand). Accuracy was assessed by computed tomography (CT), considering perforations of <2xa0mm as acceptable (safe zone). Time efficiency, radiation exposure and dependencies on surgical experience were compared between the two techniques.Results96 screws were inserted with an equal distribution of 48 screws (50xa0%) in each group. 58xa0% (nxa0=xa028) of template-guided (without fluoroscopy) vs. 44xa0% (nxa0=xa021) of free-hand screws (with fluoroscopy) were fully contained within the pedicle (pxa0=xa00.153). 97.9xa0% (nxa0=xa047) of template-guided vs. 81.3xa0% (nxa0=xa039) of free-hand screws were within the 2xa0mm safe zone (pxa0=xa00.008). The mean time for instrumentation per level was 01:14xa0±xa000:37 for the template-guided vs. 01:40xa0±xa000:59xa0min for the free-hand technique (pxa0=xa00.013), respectively. Increased radiation exposure was highly associated with lesser experience of the surgeon with the free-hand technique.ConclusionsIn a cadaver model, template-guided pedicle screw placement is faster considering intraoperative instrumentation time, has a higher accuracy particularly in the thoracic spine and creates less intraoperative radiation exposure compared to the free-hand technique.

Partial supraspinatus tears are associated with tendon lengthening

PurposeTendon tear may result in muscular retraction with the loss of contractile amplitude and strength of the rotator cuff muscles. Currently, neither a validated method of measuring supraspinatus tendon length nor normal values are known. It was therefore the purpose of this study to measure the normal length of the supraspinatus tendon and to determine whether partial tears are associated with changes in tendon length.MethodsMR examinations of 49 asymptomatic volunteers and 37 patients with arthroscopically proven, isolated partial tears of the supraspinatus tendon were compared. The ratio of the extramuscular tendon length to the distance between the footprint and the glenoid surface was calculated (TL/FG ratio). Tendon length measurements were taken by two independent readers at the bursal and articular surfaces at the anterior, the central and the posterior parts of the tendon.ResultsTL/FG ratios at the bursal surface of tendons with partial tears were significantly higher than those in the control group [anterior: 0.78xa0±xa00.20 vs. 0.66xa0±xa00.15 (pxa0<xa00.05); central: 0.61xa0±xa00.13 vs. 0.52xa0±xa00.10 (pxa0<xa00.05); posterior: 0.57xa0±xa00.15 vs. 0.52xa0±xa00.10 (pxa0<xa00.05)]. At the articular surface, differences were significant only anteriorly [0.60xa0±xa00.13, vs. 0.54xa0±xa00.10 (pxa0<xa00.05)]. A cut-off TL/FG ratio of 0.63 for measurements at the bursal surface in the center of the tendon achieved a sensitivity of 46xa0% and a specificity of 92xa0% for the identification of partial cuff tearing.ConclusionA reproducible method for measurement of extramuscular supraspinatus tendon length is described. Partial tearing of the supraspinatus tendon is associated with significant tendon lengthening, suggesting failure in continuity, and this is most reliably measured on the bursal surface.Level of evidenceIII.

Asymmetry of the multifidus muscle in lumbar radicular nerve compression

ObjectiveThe multifidus muscle is the only paraspinal lumbar muscle that is innervated by a single nerve root. This study aimes to evaluate if the asymmetry of the multifidus muscle is related to the severity of compression of the nerve root or the duration of radiculopathy.MethodsMRI scans of 79 patients with symptomatic single level, unilateral, lumbar radiculopathy were reviewed for this retrospective case series with a nested case–control study. The cross-sectional area (CSA) of the multifidus muscle and the perpendicular distance of the multifidus to the lamina (MLD) were measured bilaterally by two radiologists and set into relation to the severity of nerve compression, duration of radiculopathy and probability of an indication for surgical decompression.ResultsIn 67 recessal and 12 foraminal symptomatic nerve root compressions, neither the MLD ratio (severe 1.19u2009±u20090.55 vs less severe nerve compression: 1.12u2009±u20090.30, pu2009=u20090.664) nor the CSA ratio (severe 1u2009±u20090.16 vs less severe 0.98u2009±u20090.13, pu2009=u20090.577) nor the duration of symptoms significantly correlated with the degree of nerve compression. MR measurements of multifidus were not different in patients with (nu2009=u200920) and those without (nu2009=u200959) clinical muscle weakness in the extremity caused by nerve root compression. A MLD >1.5 was, however, associated with the probability of an indication for surgical decompression (OR 3, specificity 92xa0%, PPV 73xa0%).ConclusionsAsymmetry of the multifidus muscle correlates with neither the severity nor the duration of nerve root compression in the lumbar spine. Severe asymmetry with substantial multifidus atrophy seems associated with the probability of an indication of surgical decompression.

Biomechanical comparison of sagittal-parallel versus non-parallel pedicle screw placement

BackgroundWhile convergent placement of pedicle screws in the axial plane is known to be more advantageous biomechanically, surgeons intuitively aim toward a parallel placement of screws in the sagittal plane. It is however not clear whether parallel placement of screws in the sagittal plane is biomechanically superior to a non-parallel construct. The hypothesis of this study is that sagittal non-parallel pedicle screws do not have an inferior initial pull-out strength compared to parallel placed screws.MethodsThe established lumbar calf spine model was used for determination of pull-out strength in parallel and non-parallel intersegmental pedicle screw constructs. Each of six lumbar calf spines (L1-L6) was divided into three levels: L1/L2, L3/L4 and L5/L6. Each segment was randomly instrumented with pedicle screws (6/45xa0mm) with either the standard technique of sagittal parallel or non-parallel screw placement, respectively, under fluoroscopic control. CT was used to verify the intrapedicular positioning of all screws. The maximum pull-out forces and type of failure were registered and compared between the groups.ResultsThe pull-out forces were 5,394xa0N (range 4,221xa0N to 8,342xa0N) for the sagittal non-parallel screws and 5,263xa0N (range 3,589xa0N to 7,554xa0N) for the sagittal-parallel screws (pu2009=u20090.838). Interlevel comparisons also showed no statistically significant differences between the groups with no relevant difference in failure mode.ConclusionNon-parallel pedicle screws in the sagittal plane have at least equal initial fixation strength compared to parallel pedicle screws in the setting of the here performed cadaveric calf spine experiments.

Material-Dependent Implant Artifact Reduction Using SEMAC-VAT and MAVRIC

Objective The aim of this study was to compare the degree of artifact reduction in magnetic resonance imaging achieved with slice encoding for metal artifact correction (SEMAC) in combination with view angle tilting (VAT) and multiacquisition variable resonance image combination (MAVRIC) for standard contrast weightings and different metallic materials. Methods Four identically shaped rods made of the most commonly used prosthetic materials (stainless steel, SS; titanium, Ti; cobalt-chromium-molybdenum, CoCr; and oxidized zirconium, oxZi) were scanned at 3 T. In addition to conventional fast spin-echo sequences, metal artifact reduction sequences (SEMAC-VAT and MAVRIC) with varying degrees of artifact suppression were applied at different contrast weightings (T1w, T2w, PDw). Two independent readers measured in-plane and through-plane artifacts in a standardized manner. In addition, theoretical frequency-offset and frequency-offset-gradient maps were calculated. Interobserver agreement was assessed using intraclass correlation coefficient. Results Interobserver agreement was almost perfect (intraclass correlation coefficient, 0.86–0.99). Stainless steel caused the greatest artifacts, followed by CoCr, Ti, and oxZi regardless of the imaging sequence. While for Ti and oxZi rods scanning with weak SEMAC-VAT showed some advantage, for SS and CoCr, higher modes of SEMAC-VAT or MAVRIC were necessary to achieve artifact reduction. MAVRIC achieved better artifact reduction than SEMAC-VAT at the cost of longer acquisition times. Simulations matched well with the apparent geometry of the frequency-offset maps. Conclusions For Ti and oxZi implants, weak SEMAC-VAT may be preferred as it is faster and produces less artifact than conventional fast spin-echo. Medium or strong SEMAC-VAT or MAVRIC modes are necessary for significant artifact reduction for SS and CoCr implants. Key PointsThe amount of MR artifacts strongly depends on the prosthetic material.The effectiveness of SEMAC-VAT and MAVRIC depends on the prosthetic material and the contrast weighting.Stainless steel and cobalt-chromium-molybdenum require higher modes of SEMAC-VAT and MAVRIC compared with titanium or oxidized zirconium.

Brainstem abnormalities and vestibular nerve enhancement in acute neuroborreliosis: a case report

BackgroundBorreliosis is a widely distributed disease. Neuroborreliosis may present with unspecific symptoms and signs and often remains difficult to diagnose in patients with central nervous system symptoms, particularly if the pathognomonic erythema chronica migrans does not develop or is missed. Thus, vigilance is mandatory in cases with atypical presentation of the disease and with potentially severe consequences if not recognized early. We present a patient with neuroborreliosis demonstrating brain stem and vestibular nerve abnormalities on magnetic resonance imaging.Case presentationA 28-year-old Caucasian female presented with headaches, neck stiffness, weight loss, nausea, tremor, and gait disturbance. Magnetic resonance imaging showed T2-weighted hyperintense signal alterations in the pons and in the vestibular nerves as well as bilateral post-contrast enhancement of the vestibular nerves. Serologic testing of the cerebrospinal fluid revealed the diagnosis of neuroborreliosis.ConclusionPatients infected with neuroborreliosis may present with unspecific neurologic symptoms and magnetic resonance imaging as a noninvasive imaging tool showing signal abnormalities in the brain stem and nerve root enhancement may help in establishing the diagnosis.

Value of standard radiographs, computed tomography, and magnetic resonance imaging of the lumbar spine in detection of intraoperatively confirmed pedicle screw loosening—a prospective clinical trial

BACKGROUND CONTEXTnPedicle screw loosening is common after spinal fusion and can be associated with pseudoarthrosis and pain. With suspicion of screw loosening on standard radiographs, CT is currently considered the advanced imaging modality of choice. MRI with new metal artifact reduction techniques holds potential to be sensitive in detection of screw loosening. The sensitivity and specificity of either of the imaging modalities are yet clear.nnnPURPOSEnTo evaluate the sensitivity and specificity of three different image modalities (standard radiographs, CT, and MRI) for detection of pedicle screw loosening.nnnSTUDY DESIGN/SETTINGnCross-sectional diagnostic study.nnnPATIENT SAMPLEnForty-one patients (159 pedicle screws) undergoing revision surgeries after lumbar spinal fusion between August 2014 and April 2017 with preoperative radiographs, CT, and MRI with spinal metal artifact reduction (STIR WARP and TSE high bandwidth sequences).nnnOUTCOME MEASURESnSensitivity and specificity in detection of screw loosening for each imaging modality.nnnMETHODSnScrew torque force was measured intraoperatively and compared with preoperative screw loosening signs such as peri-screw edema in MRI and peri-screw osteolysis in CT and radiographs. A torque force of less than 60 Ncm was used to define a screw as loosened.nnnRESULTSnSensitivity and specificity in detection of screw loosening was 43.9% and 92.1% for MRI, 64.8% and 96.7% for CT, and 54.2% and 83.5% for standard radiographs, respectively.nnnCONCLUSIONSnDespite improvement of MRI with metal artifact reduction MRI technique, CT remains the modality of choice. Even so, CT fails to detect all loosened pedicle screws.