Multiple single-point imaging (mSPI) as a tool for capturing and characterizing MR signals and repetitive signal disturbances with high temporal resolution: the MRI scanner as a high-speed camera.

In this paper we aim to lay down and demonstrate the use of multiple single-point imaging (mSPI) as a tool for capturing and characterizing steady-state MR signals and repetitive disturbances thereof with high temporal resolution. To achieve this goal, various 2D mSPI sequences were derived from the nearest standard 3D imaging sequences by (i) replacing the excitation of a 3D slab by the excitation of a 2D slice orthogonal to the read axis, (ii) setting the readout gradient to zero, and (iii) leaving out the inverse Fourier transform in the read direction. The thus created mSPI sequences, albeit slow with regard to the spatial encoding part, were shown to result into a series of densely spaced 2D single-point images in the time domain enabling monitoring of the evolution of the magnetization with a high temporal resolution and without interference from any encoding gradients. The high-speed capabilities of mSPI were demonstrated by capturing and characterizing the free induction decays and spin echoes of substances with long T2s (>30 ms) and long and short T2*s (4 - >30 ms) and by monitoring the perturbation of the transverse magnetization by, respectively, a titanium cylinder, representing a static disturbance; a pulsed magnetic field gradient, representing a stimulus inherent to a conventional MRI experiment; and a pulsed electric current, representing an external stimulus. The results of the study indicate the potential of mSPI for assessing the evolution of the magnetization and, when properly synchronized with the acquisition, repeatable disturbances thereof with a temporal resolution that is ultimately limited by the bandwidth of the receiver, but in practice governed by the SNR of the experiment and the magnitude of the disturbance. Potential applications of mSPI can be envisaged in research areas that are concerned with MR signal behavior, MR system performance and MR evaluation of magnetically evoked responses.

Accuracy of gadofosveset-enhanced MRI for nodal staging and restaging in rectal cancer.

OBJECTIVE: To prospectively assess the accuracy of gadofosveset-enhanced magnetic resonance imaging (MRI) for nodal staging and restaging in rectal cancer. BACKGROUND: Accurate preoperative assessment of nodal disease in rectal cancer impacts treatment management. Staging with modern imaging techniques (computed tomography, MRI and endorectal ultrasound) is insufficiently accurate for clinical decision making. This study aims to assess the accuracy of MRI using a novel lymph node magnetic resonance contrast, gadofosveset, for nodal staging and restaging in rectal cancer using a per node comparison with histology as the reference standard. METHODS: Sixty-eight patients underwent gadofosveset-enhanced MRI at 1.5T. Twenty-six patients (primary staging group I) were treated with total mesorectal excision (with or without preoperative 5 × 5 Gy) and 42 (restaging group II) underwent a long course of chemoradiation followed by a restaging MRI and resection. Nodes were scored as benign or malignant by 2 radiologists (experienced and junior reader) first on standard MRI, then on gadofosveset-enhanced MRI. For group I the primary staging MRI was compared with histology. In group II the second, restaging MRI was compared with histology. RESULTS: For the experienced reader, sensitivity, specificity, and area under the ROC-curve (AUC) improved from 76%, 82% and 0.84 on standard MRI to 80%, 97% and 0.96 on gadofosveset-MRI (P < 0.001). For the junior reader results improved from 69%, 85%, and 0.85 on standard MRI to 70%, 95%, and 0.93 on gadofosveset-MRI (P = 0.03). Interobserver agreement was good on both standard MRI (κ 0.73) and gadofosveset-MRI (κ 0.71). CONCLUSIONS: This study shows high reproducibility and significantly improved accuracy compared to standard MRI for gadofosveset-enhanced MRI for nodal staging and restaging in rectal cancer.

Value of ADC measurements for nodal staging after chemoradiation in locally advanced rectal cancer-a per lesion validation study.

OBJECTIVES: To evaluate the performance of diffusion-weighted MRI (DWI) in addition to T2-weighted (T2W) MRI for nodal restaging after chemoradiation in rectal cancer. METHODS: Thirty patients underwent chemoradiation followed by MRI (1.5 T) and surgery. Imaging consisted of T2W-MRI and DWI (b0, 500, 1000). On T2W-MRI, nodes were scored as benign/malignant by two independent readers (R1, R2). Mean apparent diffusion coefficient (ADC) was measured for each node. Diagnostic performance was compared for T2W-MRI, ADC and T2W+ADC, using a per lesion histological validation. RESULTS: ADC was higher for the malignant nodes (1.43 ± 0.38 vs 1.19 ± 0.27 *10⁻³ mm²/s, p < 0.001). Area under the ROC curve/sensitivity/specificity were 0.88/65%/93% (R1) and 0.95/71%/91% (R2) using T2W-MRI; 0.66/53%/82% using ADC (mean of two readers); and 0.91/56%/98% (R1) and 0.96/56%/99% (R2) using T2W+ADC. There was no significant difference between T2W-MRI and T2W+ADC. Interobserver reproducibility was good for T2W-MRI (κ0.73) and ADC (intraclass correlation coefficient 0.77). CONCLUSIONS: After chemoradiation, ADC measurements may have potential for nodal characterisation, but DWI on its own is not reliable. Addition of DWI to T2W-MRI does not improve accuracy and T2W-MRI is already sufficiently accurate.

Free-breathing MRI for the assessment of myocardial infarction: clinical validation.

OBJECTIVE: The objective of our study was to validate free-breathing 2D inversion recovery delayed-enhancement MRI for the assessment of myocardial infarction compared with a breath-hold 3D technique. SUBJECTS AND METHODS: Institutional review board approval and written informed consent were obtained. Thirty-two patients (25 men, seven women; mean age, 68 years; age range, 39-84 years) underwent breath-hold gradient-echo 3D inversion-recovery delayed-enhancement MRI and free-breathing respiratory-triggered 2D inversion-recovery delayed-enhancement MRI of the heart (scanning time, 50-80 seconds). Infarct size was quantitatively analyzed as a percentage of the left ventricle. The location and transmural extent of myocardial infarction were assessed by visual scoring. Intraclass correlation and Bland-Altman analysis were used to evaluate the agreement between the techniques for infarct quantification. Kappa statistics were used to analyze the visual score. RESULTS: Excellent agreement between the two techniques was observed for infarct quantification (intraclass correlation = 0.99 [p < 0.01]; mean difference +/- SD = 0.32% +/- 2.4%). The agreement in assessing transmural extent of infarction was good to excellent between the free-breathing technique and the 3D breath-hold technique (kappa varied between 0.70 and 0.96 for all segments). No regions of infarction were missed using the free-breathing approach. CONCLUSION: The free-breathing 2D delayed-enhancement MRI sequence is a fast and reliable tool for detecting myocardial infarction.