An Alzheimer's Disease Genetic Risk Score Predicts Longitudinal Thinning of Hippocampal Complex Subregions in Healthy Older Adults.

Variants at 21 genetic loci have been associated with an increased risk for Alzheimer's disease (AD). An important unresolved question is whether multiple genetic risk factors can be combined to increase the power to detect changes in neuroimaging biomarkers for AD. We acquired high-resolution structural images of the hippocampus in 66 healthy, older human subjects. For 45 of these subjects, longitudinal 2-year follow-up data were also available. We calculated an additive AD genetic risk score for each participant and contrasted this with a weighted risk score (WRS) approach. Each score included APOE (apolipoprotein E), CLU (clusterin), PICALM (phosphatidylinositol binding clathrin assembly protein), and family history of AD. Both unweighted risk score (URS) and WRS correlated strongly with the percentage change in thickness across the whole hippocampal complex (URS: r = -0.40; p = 0.003; WRS: r = -0.25, p = 0.048), driven by a strong relationship to entorhinal cortex thinning (URS: r = -0.35; p = 0.009; WRS: r = -0.35, p = 0.009). By contrast, at baseline the risk scores showed no relationship to thickness in any hippocampal complex subregion. These results provide compelling evidence that polygenic AD risk scores may be especially sensitive to structural change over time in regions affected early in AD, like the hippocampus and adjacent entorhinal cortex. This work also supports the paradigm of studying genetic risk for disease in healthy volunteers. Together, these findings will inform clinical trial design by supporting the idea that genetic prescreening in healthy control subjects can be useful to maximize the ability to detect an effect on a longitudinal neuroimaging endpoint, like hippocampal complex cortical thickness.

Detection of implants and other objects using a ferromagnetic detection system: implications for patient screening before MRI.

OBJECTIVE: Ferromagnetic detection systems have been used to prevent accidents related to external ferromagnetic objects (e.g., pocket knives, hearing aids, and so on). If a ferromagnetic implant was missed during MRI screening, the ability to use a ferromagnetic detection system to discover the object in a patient before MRI could potentially avoid a serious injury, which has important implications for patient safety. Therefore, the purpose of this investigation was to use a ferromagnetic detection system to assess implants and other objects that may be encountered in patients referred for MRI procedures. MATERIALS AND METHODS: A "pillar-type" ferromagnetic detection system was used to evaluate 67 different implants and other objects (pulse generators [n = 43], electronic devices [n = 5], stents [n = 6], CSF shunt valves [n = 3], orthopedic implants [n = 3], bullets [n = 4], and others [n = 3]) that were attached to a volunteer subject's body to approximate a realistic in situ location. The subject with the test item approached the ferromagnetic detection system, rotated in front of it four times, and withdrew while the alarms were monitored and recorded. RESULTS: There were 58 true-positive, four true-negative, no false-positive, and five false-negative findings. Thus, the sensitivity was 92% and the specificity was 100%. CONCLUSIONS: These results indicated that, besides being used to identify external ferromagnetic objects, this ferromagnetic detection system may be a useful tool to screen patients referred for MRI examinations who may have implanted or embedded items. Further investigation to determine the use of this ferromagnetic detection system to detect additional implants in the clinical setting is warranted.

In vitro assessment of a fiducial marker for lung lesions: MRI issues at 3 T.

OBJECTIVE: The objective of our study was to assess MRI issues at 3 T for a newly developed fiducial marker used to localize lung lesions. MATERIALS AND METHODS: A fiducial marker designed for lung lesions (super-Lock Cobra) was investigated at 3 T for magnetic field interactions, MRI-related heating, and artifacts using standardized techniques. Magnetic field interactions were assessed with regard to translational attraction and torque. MRI-related heating was characterized by placing the marker in a gelled-saline-filled head-torso phantom and performing MRI using a transmit-receive radiofrequency body coil at an MR system-reported, whole-body-averaged specific absorption rate of 2.9 W/kg for 15 minutes. Artifacts were measured for the marker on MR images obtained using T1-weighted spin-echo and gradient-echo pulse sequences. RESULTS: The fiducial marker displayed very low magnetic field interactions (2° deflection angle and no torque) at 3 T. MRI-related heating was at the same level as the "background" (i.e., phantom heating without the marker) temperature rise. Artifacts were relatively small in relation to the size and shape of the marker. CONCLUSION: The results of this investigation show that there are no MRI-related safety concerns and, thus, that it would be acceptable (i.e., "MR conditional") for a patient with this new fiducial marker to be examined using MRI at 3 T or less. Artifacts, although relatively small, may create issues if the area of interest is the same as that of the marker or if the interpreting radiologist does not know the marker is present.

Armor-piercing bullet: 3-T MRI findings and identification by a ferromagnetic detection system.

The objective of this project was to evaluate magnetic resonance imaging (MRI) issues at 3 T for an armor-piercing bullet and to determine if this item could be identified using a ferromagnetic detection system. An armor-piercing bullet (.30 caliber, 7.62 × 39, copper-jacketed round, steel core; Norinco) underwent evaluation for magnetic field interactions, heating, and artifacts using standardized techniques. Heating was assessed with the bullet in a gelled-saline-filled phantom with MRI performed using a transmit/receive radio frequency body coil at a whole-body-averaged specific absorption rate of 2.9 W/kg for 15 minutes. Artifacts were characterized using T1-weighted spin echo and gradient echo pulse sequences. In addition, a special ferromagnetic detection system (Ferroguard Screener; Metrasens, Lisle, Illinois) was used in an attempt to identify this armor-piercing bullet. The findings indicated that the armor-piercing bullet showed substantial magnetic field interactions. Heating was not excessive. Artifacts were large and may create diagnostic problems if the area of interest is close to this bullet. The ferromagnetic detection system yielded a positive result. We concluded that this armor-piercing bullet is MR unsafe. Importantly, this ballistic item was identified using the particular ferromagnetic detection system utilized in this investigation, which has important implications for MRI screening and patient safety.

MRI issues for ballistic objects: information obtained at 1.5-, 3- and 7-Tesla.

BACKGROUND CONTEXT: Few studies exist for magnetic resonance imaging (MRI) issues and ballistics, and there are no studies addressing movement, heating, and artifacts associated with ballistics at 3-tesla (T). Movement because of magnetic field interactions and radiofrequency (RF)-induced heating of retained bullets may injure nearby critical structures. Artifacts may also interfere with the diagnostic use of MRI. PURPOSE: To investigate these potential hazards of MRI on a sample of bullets and shotgun pellets. STUDY DESIGN: Laboratory investigation, ex vivo. METHODS: Thirty-two different bullets and seven different shotgun pellets, commonly encountered in criminal trauma, were assessed relative to 1.5-, 3-, and 7-T magnetic resonance systems. Magnetic field interactions, including translational attraction and torque, were measured. A representative sample of five bullets were then tested for magnetic field interactions, RF-induced heating, and the generation of artifacts at 3-T. RESULTS: At all static magnetic field strengths, non-steel-containing bullets and pellets exhibited no movement, whereas one steel core bullet and two steel pellets exhibited movement in excess of what might be considered safe for patients in MRI at 1.5-, 3- and 7-Tesla. At 3-T, the maximum temperature increase of five bullets tested was 1.7°C versus background heating of 1.5°C. Of five bullets tested for artifacts, those without a steel core exhibited small signal voids, whereas a single steel core bullet exhibited a very large signal void. CONCLUSIONS: Ballistics made of lead with copper or alloy jackets appear to be safe with respect to MRI-related movement at 1.5-, 3-, and 7-T static magnetic fields, whereas ballistics containing steel may pose a danger if near critical body structures because of strong magnetic field interactions. Temperature increases of selected ballistics during 3-T MRI was not clinically significant, even for the ferromagnetic projectiles. Finally, ballistics containing steel generated larger artifacts when compared with ballistics made of lead with copper and alloy jackets and may impair the diagnostic use of MRI.

A next-generation, flow-diverting implant used to treat brain aneurysms: in vitro evaluation of magnetic field interactions, heating and artifacts at 3-T.

BACKGROUND AND PURPOSE: Fine-mesh braided, stent-like structures (flow diverters) have been proposed for treatment of brain aneurysms. To date, the safety of performing magnetic resonance imaging (MRI) in patients with these implants is unknown. Therefore, the purpose of this study was to evaluate MRI issues at 3-T for a new flow-diverting implant used to treat brain aneurysms. METHODS: The Surpass NeuroEndoGraft (Surpass Medical, Ltd., Tel Aviv, Israel) underwent evaluation for magnetic field interactions, MRI-related heating and artifacts using standardized techniques. Magnetic field interactions were assessed for this implant with regard to translational attraction (i.e., using the deflection angle technique) and torque (qualitative assessment method). MRI-related heating was evaluated by placing the implant in a gelled-saline-filled, head/torso phantom and performing MRI using a transmit/receive radiofrequency body coil at a whole-body-averaged specific absorption rate of 2.9 W/kg for 15 min. Artifacts were characterized using T1-weighted, spin echo (SE) and gradient echo (GRE) pulse sequences. RESULTS: The Surpass NeuroEndoGraft exhibited minor magnetic field interactions (21° deflection angle and no torque), which were acceptable from a safety consideration. Heating was not substantial, with the highest temperature change being 2.3°C (background temperature rise without the implant was 1.5°C). Artifacts may create issues if the area of interest is in the same area or close to this implant. CONCLUSIONS: The findings demonstrated that it would be acceptable for patients with this next-generation, flow-diverting implant to undergo MRI at 3-T or less.