MRI in patients with implanted active devices: how to combine safety and image quality using a limited transmission field?

OBJECTIVES: Radio frequency (RF) pulses in magnetic resonance imaging (MRI) can interact with implanted devices and cause tissue damage. However, there are new devices that can safely perform measurements with liberal MRI conditions such as an RF transmission field B1+rms ≤ 2.0 µT. We investigated whether MRI in this case is limited for these technical reasons. METHODS: We selected typical MRI protocols of six body regions (brain, cervical spine, lumbar spine, knee, liver, heart) using two typical 1.5T MRI scanners. Overall, we adapted 62 sequences to B1+rms conditions and evaluated their diagnostic quality. For this, we measured signal-to-noise-ratio (SNR), contrast-to-noise-ratio (CNR), and geometric deviation (GD) as quality parameters, using phantom studies. For questionnaire studies, we selected pairs of original and adapted sequences in healthy volunteers. Blinded radiologists rated the images as single sequence rating and in direct comparison. RESULTS: Roughly one-third of the checked sequences were below the B1+rms limit. Here, 56 of the 62 adapted sequences showed at least the same image quality in single ratings. A reduction in SNR and/or CNR was found with 31 sequences and only one sequence with considerably increased GD. Especially, sequences with original high B1+rms values, PD sequences, and sequences of the Siemens knee and heart protocol were difficult to adapt, whereas most TSE and IR sequences had no clinical limitations. CONCLUSION: By limiting the transmission field to B1+rms ≤ 2.0 µT, clinically relevant MR sequences can be adapted with nearly no reduction in image quality. Despite limiting the transmission field, high-quality MR imaging is possible. We could derive strategies for adaptation. KEY POINTS: • Despite limiting the transmission field, high-quality MRI is possible. • We could derive strategies for adapting the sequences to B1+rms≤ 2.0 µT. • This enables high-quality MRI of different body regions for patients with AD.

IRMA Code II: unique annotation of medical images for access and retrieval.

Content-based image retrieval (CBIR) provides novel options to access large repositories of medical images, in particular for storing, querying and reporting. This requires a revisit of nomenclatures for image classification such as DICOM, SNOMED, and RadLex. For instance, DICOM defines only about 20 concept terms for body regions, which partly overlap. This is insufficient to access the visual image characteristics. In 2002, the Image Retrieval in Medical Applications (IRMA) project proposed a mono-hierarchic, multi-axial coding scheme called IRMA Code. It was used in the Cross Language Evaluation Forum (ImageCLEF) annotation tasks. Ten years of experience have discovered several weak points. In this paper, we propose eight axes of three levels in hierarchy for (A) anatomy, (B) biological system, (C) configuration, (D) direction, (E) equipment, (F) finding, (G) generation, and (H) human maneuver as well as additional flags for age class, body side, contrast agent, ethnicity, finding certainty, gender, quality, and scanned film, which are captured in form of another axis (I). Using a tag-based notation IRMA Code II supports multiple selection coding within one axis, which is required for the new main categories.

Practicability and Diagnostic Yield of One-Stop Stroke CT with Delayed-Phase Cardiac CT in Detecting Major Cardioembolic Sources of Acute Ischemic Stroke : A Proof of Concept Study.

PURPOSE: Recurrent stroke is considered to increase the incidence of severe disability and death. For correct risk assessment and patient management it is essential to identify the origin of stroke at an early stage. Transthoracic echocardiography (TTE) is the initial standard of care for evaluating patients in whom a cardioembolic source of stroke (CES) is suspected but its diagnostic capability is limited. Transesophageal echocardiography (TEE) is considered as gold standard; however, this approach is time consuming, semi-invasive and not always feasible. We hypothesized that adding a delayed-phase cardiac computed tomography (cCT) to initial multimodal CT might represent a valid alternative to routine clinical echocardiographic work-up. MATERIAL AND METHODS: Patients with suspected acute cardioembolic stroke verified by initial multimodal CT and subsequently examined with cCT were included. The cCT was evaluated for presence of major CES and compared to routine clinical echocardiographic work-up. RESULTS: In all, 102 patients with suspected acute CES underwent cCT. Among them 60 patients underwent routine work-up with echocardiography (50 TTE and only 10 TEE). By cCT 10/60 (16.7%) major CES were detected but only 4 (6.7%) were identified by echocardiography. All CES observed by echocardiography were also detected by cCT. In 8 of 36 patients in whom echocardiography was not performed cCT also revealed a major CES. CONCLUSION: These preliminary results show the potential diagnostic yield of delayed-phase cCT to detect major CES and therefore could accelerate decision-making to prevent recurrence stroke. To confirm these results larger studies with TEE as the reference standard and also compared to TTE would be necessary.

Non-contrast enhanced diagnosis of acute myocarditis based on the 17-segment heart model using 2D-feature tracking magnetic resonance imaging.

PURPOSE: The aim of this study was to investigate the diagnostic value of myocardial deformation analysis based on the 17-segment heart model using non-contrast enhanced (CE) 2D tissue feature tracking (2D-FT) technique. MATERIAL AND METHODS: Seventy patients with suspected myocarditis underwent a cardiovascular magnetic resonance (CMR) examination at 1.5 Tesla. A contrast-agent-free part of this CMR protocol was additionally performed in forty healthy volunteers (HV). Besides standard CMR data sets, 2D-FT derived segmental and global longitudinal, radial, and circumferential deformation parameters were analyzed. The 2D-FT results were compared to the combined findings from CMR imaging and endomyocardial biopsy (EMB). RESULTS: Patients were assigned to three groups depending on their ejection fraction (EF) (<40%, 40-55%, ≥55%). Compared to HV, impaired EF (<55%) was significantly correlated to reduced segmental and global strain and strain rate values. The circumferential deformation analysis was more sensitive to myocardial changes than longitudinal and radial analysis. The segmental strain/strain rate had an accuracy of 84.3%/70.0% for the diagnosis of an acute myocarditis, stated by EMB and CMR in 42 of 70 patients. In patients with preserved EF, acute myocarditis could be ruled out using only segmental strain analysis with a negative predictive value of 87.5%. CONCLUSION: In patients with suspected myocarditis, the deformation analysis based on the 17-segment heart model provides valuable information about functional myocardial inhomogeneity. This quantitative approach could be used in addition to the clinical standard CMR protocol and represents a promising tool in the framework of a prospective automatized multiparametric CMR imaging analysis.