Measuring the apparent diffusion coefficient in primary rectal tumors: is there a benefit in performing histogram analyses?

PURPOSE: The apparent diffusion coefficient (ADC) is a potential prognostic imaging marker in rectal cancer. Typically, mean ADC values are used, derived from precise manual whole-volume tumor delineations by experts. The aim was first to explore whether non-precise circular delineation combined with histogram analysis can be a less cumbersome alternative to acquire similar ADC measurements and second to explore whether histogram analyses provide additional prognostic information. METHODS: Thirty-seven patients who underwent a primary staging MRI including diffusion-weighted imaging (DWI; b0, 25, 50, 100, 500, 1000; 1.5 T) were included. Volumes-of-interest (VOIs) were drawn on b1000-DWI: (a) precise delineation, manually tracing tumor boundaries (2 expert readers), and (b) non-precise delineation, drawing circular VOIs with a wide margin around the tumor (2 non-experts). Mean ADC and histogram metrics (mean, min, max, median, SD, skewness, kurtosis, 5th-95th percentiles) were derived from the VOIs and delineation time was recorded. Measurements were compared between the two methods and correlated with prognostic outcome parameters. RESULTS: Median delineation time reduced from 47-165 s (precise) to 21-43 s (non-precise). The 45th percentile of the non-precise delineation showed the best correlation with the mean ADC from the precise delineation as the reference standard (ICC 0.71-0.75). None of the mean ADC or histogram parameters showed significant prognostic value; only the total tumor volume (VOI) was significantly larger in patients with positive clinical N stage and mesorectal fascia involvement. CONCLUSION: When performing non-precise tumor delineation, histogram analysis (in specific 45th ADC percentile) may be used as an alternative to obtain similar ADC values as with precise whole tumor delineation. Histogram analyses are not beneficial to obtain additional prognostic information.

Automated multiscale vessel analysis for the quantification of MR angiography of peripheral arteriogenesis.

PURPOSE: To automatically analyze the time course of collateralization in a rat hindlimb ischemia model based on signal intensity distribution (SID). MATERIALS AND METHODS: Time-of-flight magnetic resonance angiograms (TOF-MRA) were acquired in eight rats at 2, 7, and 21 days after unilateral femoral artery ligation. Analysis was performed on maximum intensity projections filtered with multiscale vessel enhancement filter. Differences in SID between ligated limb and a reference region were monitored over time and compared to manual collateral artery identification. RESULTS: The differences in SID correlated well with the number of collateral arteries found with manual quantification. The time courses of ultrasmall (diameter ≪0.5 mm) and small (diameter ≈0.5 mm) collateral artery development could be differentiated, revealing that maturation of the collaterals and enlargement of their feeding arteries occurred mainly after the first week postligation. CONCLUSION: SID analysis performed on axial maximum intensity projections is easy to implement, fast, and objective and provides more insight in the time course of arteriogenesis than manual identification.

MRI of renal oxygenation and function after normothermic ischemia-reperfusion injury.

The in vivo assessment of renal damage after ischemia-reperfusion injury, such as in sepsis, hypovolemic shock or after transplantation, is a major challenge. This injury often results in temporary or permanent nonfunction. In order to improve the clinical outcome of the kidneys, novel therapies are currently being developed that limit renal ischemia-reperfusion injury. However, to fully address their therapeutic potential, noninvasive imaging methods are required which allow the in vivo visualization of different renal compartments and the evaluation of kidney function. In this study, MRI was applied to study kidney oxygenation and function in a murine model of renal ischemia-reperfusion injury at 7 T. During ischemia, there was a strongly decreased oxygenation, as measured using blood oxygen level-dependent MRI, compared with the contralateral control, which persisted after reperfusion. Moreover, it was possible to visualize differences in oxygenation between the different functional regions of the injured kidney. Dynamic contrast-enhanced MRI revealed a significantly reduced renal function, comprising perfusion and filtration, at 24 h after reperfusion. In conclusion, MRI is suitable for the noninvasive evaluation of renal oxygenation and function. Blood oxygen level-dependent or dynamic contrast-enhanced MRI may allow the early detection of renal pathology in patients with ischemia-reperfusion injury, such as in sepsis, hypovolemic shock or after transplantation, and consequently may lead to an earlier intervention or change of therapy to minimize kidney damage.

Molecular magnetic resonance imaging of myocardial angiogenesis after acute myocardial infarction.

BACKGROUND: Angiogenesis is a natural mechanism to restore perfusion to the ischemic myocardium after acute myocardial infarction (MI). Therapeutic angiogenesis is being explored as a novel treatment for MI patients; however, sensitive, noninvasive in vivo measures of therapeutic efficacy are lacking and need to be developed. Here, a molecular magnetic resonance imaging method is presented to noninvasively image angiogenic activity in vivo in a murine model of MI with cyclic Asn-Gly-Arg (cNGR)-labeled paramagnetic quantum dots (pQDs). The tripeptide cNGR homes specifically to CD13, an aminopeptidase that is strongly upregulated during myocardial angiogenesis. METHODS AND RESULTS: Acute MI was induced in male Swiss mice via permanent ligation of the left anterior descending coronary artery. Molecular magnetic resonance imaging was performed 7 days after surgery and up to 2 hours after intravenous contrast agent administration. Injection of cNGR-pQDs resulted in a strong negative contrast that was located mainly in the infarcted myocardium. This negative contrast was significantly less in MI mice injected with unlabeled pQDs and in sham-operated mice injected with cNGR-pQDs. Validation with ex vivo 2-photon laser scanning microscopy revealed a strong colocalization of cNGR-pQDs with vascular endothelial cells, whereas unlabeled pQDs were mostly extravasated and diffused through the tissue. Additionally, 2-photon laser scanning microscopy demonstrated significant microvascular remodeling in the infarct/border zones compared with remote myocardium. CONCLUSIONS: cNGR-pQDs allow selective, noninvasive detection of angiogenic activity in the infarcted heart with the use of in vivo molecular magnetic resonance imaging and ex vivo 2-photon laser scanning microscopy.