Optimization of saturation-recovery dynamic contrast-enhanced MRI acquisition protocol: monte carlo simulation approach demonstrated with gadolinium MR renography

Exercise-induced calf muscle hyperemia: quantitative mapping with low-dose dynamic contrast enhanced magnetic resonance imaging

Peripheral artery disease (PAD) in the lower extremities often leads to intermittent claudication. In the present study, we proposed a low-dose DCE MRI protocol for quantifying calf muscle perfusion stimulated with plantar flexion and multiple new metrics for interpreting perfusion maps, including the ratio of gastrocnemius over soleus perfusion (G/S; for assessing the vascular redistribution between the two muscles) and muscle perfusion normalized by whole body perfusion (for quantifying the muscle's active hyperemia). Twenty-eight human subjects participated in this Institutional Review Board-approved study, with 10 healthy subjects ( group A) for assessing interday reproducibility and 8 healthy subjects ( group B) for exploring the relationship between plantar-flexion load and induced muscle perfusion. In a pilot group of five elderly healthy subjects and five patients with PAD ( group C), we proposed a protocol that measured perfusion for a low-intensity exercise and for an exhaustion exercise in a single MRI session. In group A, perfusion estimates for calf muscles were highly reproducible, with correlation coefficients of 0.90-0.93. In group B, gastrocnemius perfusion increased linearly with the exercise workload ( P < 0.05). With the low-intensity exercise, patients with PAD in group C showed substantially lower gastrocnemius perfusion compared with elderly healthy subjects [43.4 (SD 23.5) vs. 106.7 (SD 73.2) ml·min^-1·100 g^-1]. With exhaustion exercise, G/S [1.0 (SD 0.4)] for patients with PAD was lower than both its low-intensity level [1.9 (SD 1.3)] and the level in elderly healthy subjects [2.7 (SD 2.1)]. In conclusion, the proposed MRI protocol and the new metrics are feasible for quantifying exercise-induced muscle hyperemia, a promising functional test of PAD. NEW & NOTEWORTHY To quantitatively map exercise-induced hyperemia in calf muscles, we proposed a high-resolution MRI method shown to be highly reproducible and sensitive to exercise load. With the use of low contrast, it is feasible to measure calf muscle hyperemia for both low-intensity and exhaustion exercises in a single MRI session. The newly proposed metrics for interpreting perfusion maps are promising for quantifying intermuscle vascular redistribution or a muscle's active hyperemia.

Value of Magnetic Resonance Urography Versus Computerized Tomography Urography (CTU) in Evaluation of Obstructive Uropathy: An Observational Study

BACKGROUND

Obstructive uropathy is a common public health issue that requires imaging research for providing necessary information. The data is important for determining treatment options, and may influence selective management choices.

OBJECTIVE

The aim of the study is to determine whether magnetic resonance urography or computerized tomography urography is the best imaging modality among patients with suspected obstructive uropathy.

METHODS

Seventy patients; referred from the emergency department for the evaluation of renal colic or hematuria that highly suggested urinary tract abnormalities, were prospectively enrolled. Thirty five women and 35 men were categorized with a mean age of 43.52 years and the mean body weight of 61.31 kg. All participants underwent abdominal ultrasonography and clinical examination to detect the causes of urinary obstruction. Pregnant women were excluded from the study. Both magnetic resonance urography and computerized tomography urography were performed within 30 days of each analysis.

RESULTS

Only 54.3% of the participants had urinary stones. Mean size of the renal stone was 11 mm; while mean size of the ureteral stone was 3.8 mm. The approach of magnetic resonance is not only limited to diagnosis, but is also effectively involved in the real time investigations. MRU has more reliability in terms of the diagnosis and anatomic presentation of the kidneys along with the vasculature. All cases of urinary stones were detected by computed tomography (100%); whereas, 78.9% cases were detected by magnetic resonance urography.

CONCLUSION

Computerized tomography urography is more sensitive in detecting kidney stones; whereas, magnetic resonance urography is better in detecting pathology behind the development of kidney stones.