Comparison of single-breath-hold fast spin-echo sequences with routine non-breath-hold techniques: application to MRI of renal masses

Magnetic resonance imaging of the upper abdomen using a free-breathing T2-weighted turbo spin echo sequence with navigator triggered prospective acquisition correction

PURPOSE

To evaluate a free-breathing navigator triggered T2-weighted turbo spin-echo sequence with prospective acquisition correction (T2w-PACE-TSE) for MRI of the upper abdomen in comparison to a conventional T2-weighted TSE (T2w-CTSE), a single-shot TSE (T2w-HASTE), and a T1-weighted gradient-echo sequence (T1w-FLASH).

MATERIALS AND METHODS

A total of 40 consecutive patients were examined at 1.5 T using free-breathing T2w-PACE-TSE, free-breathing T2w-CTSE, and breath-hold T2w-HASTE and T1w-FLASH acquisition. Images were evaluated qualitatively by three radiologists regarding motion artifacts, liver-spleen contrast, depiction of intrahepatic vessels, the pancreas and the adrenal glands, and overall image quality on a four-point scale. Quantitative analysis of the liver-spleen contrast was performed.

RESULTS

Depiction and sharpness of intrahepatic vessels were rated significantly better (P < 0.01) using T2w-PACE-TSE compared to T2w-CTSE and T2w-HASTE sequences. Significantly higher contrast values were measured for T2w-PACE-TSE images compared to T2w-CTSE, T2w-HASTE, and T1w-FLASH images (P < 0.01). Mean examination time of the T2w-PACE-TSE was 7.91 minutes, acquisition time of the T2w-CTSE sequence was 4.52 minutes.

CONCLUSION

Prospective acquisition correction is an efficient method for reducing respiratory movement artifacts in T2w-TSE imaging of the upper abdomen. Compared to T2w-CTSE and T2w-HASTE sequences recognition of anatomical details and contrast can be significantly improved.

Imaging of renal lesions: evaluation of fast MRI and helical CT

The purpose of this study is to compare triphasic helical CT and fast MRI with respect to detection, characterization and staging of suspected renal masses. To achieve this triphasic helical CT (plain, corticonephrographic and tubulonephrographic phase) and MRI with fast T(1) weighted and T(2) weighted sequences were performed in 29 patients with a suspected renal lesion. Image quality, lesion characterization and lesion extent were assessed for both methods in all patients. The acquisition phase for CT and the image sequence for MRI offering the best image quality and best diagnostic information regarding renal parenchyma, renal vessels, detection of enlarged lymph nodes, and other abdominal organs were determined. Histologically confirmed renal cell carcinomas (n=18) were staged based on the Robson classification. Quantitative data were obtained from operator-defined regions of interest (ROIs) in all acquisition phases (CT) and all image sequences (MRI). For most criteria the rating of image quality for helical CT was generally higher as compared with fast MRI. CT and MRI detected all 24 histologically proven masses, while no false positive solid tumour was diagnosed with both imaging modalities. All three acquisition phases in CT and all applied image sequences in MRI were regarded as necessary in order to gain important diagnostic information. Altogether, 12 of 18 renal cell carcinomas (67%) were correctly staged by CT and MRI. Helical CT and fast MRI allow the correct detection and characterization of suspicious renal lesions. Both imaging modalities can be recommended for clinical routine application. Although the correct histological staging of renal cancer remains difficult for both imaging methods, both are excellent in providing the critical staging information needed before surgery. Helical CT offers a significantly shorter acquisition time to cover the entire abdomen.

T2-weighted breathold imaging of the liver: a quantitative and qualitative comparison of fast spin echo and half Fourier single shot fast spin echo imaging

The imaging characteristics of two EPI-hybrid breath-hold sequences, T2-weighted fast spin-echo [FSE, effective echo time (TEeff) 138 ms] and half Fourier single shot turbo spin-echo (HASTE, TEeff 60 ms), were compared in hepatic imaging. A total of 111 patients with suspected hepatic disease were studied at 1.5 Tesla using a body phase-array coil. The signal-to-noise (S/N) and contrast-to-noise (C/N) ratios for organs and lesions were calculated and quantitatively compared. Organ delineation, visualization of anatomical structures and pathological lesions, artifacts, and total image quality were qualitatively assessed and statistically compared. The final diagnoses were metastases from colorectal, breast, and pancreatic cancer in 23/111, hepatocellular carcinoma in 15/111, cysts in 19/111, hemangiomas in 9/111, several other lesions in 7/111, and no lesions in 38/111 of the cases. A total of 139 lesion in 73% of the patients were seen while 85% of the lesions were at least 1.5 cm in size. Regarding S/Ns HASTE was significantly (P < 0.03) superior to FSE with only minor (P > 0.05) differences in C/Ns between the two sequences for anatomical and pathological structures. HASTE demonstrated in almost all (97.3%) of the cases no artifacts, while on fast SE imaging moderate to minor artifacts were present in 23.5-51.7% of the cases. The overall image quality and diagnostic confidence was rated significantly higher (good 43.2%, excellent 53.2%) for HASTE than for fast SE imaging (good 44.8%, excellent 17.6%). Providing comparable C/Ns for anatomical and pathological structures, breatheld HASTE imaging proved to be superior to fast SE in T2-weighted imaging of the upper abdomen regarding general image quality, and, with adequate technical prerequisites, may be a suitable substitute of fast T2-imaging techniques.

Fast and ultrafast magnetic resonance imaging in renal lesions

Our purpose was to analyze and compare the image quality and contrast-to-noise ratio (CNR) of different fast T1- and T2-weighted sequences with conventional spin-echo sequences in renal MRI. Twenty-three patients with focal renal lesions were examined with a T2-weighted ultrafast turbo spin-echo (UTSE) sequence with and without frequency selective fat suppression (SPIR), a combined gradient-and-spin-echo sequence (GraSE), and a conventional spin-echo sequence (SE). In addition, T1-weighted images were obtained pre- and postcontrast, using a fast spin-echo sequence (TSE) with and without SPIR and the conventional SE sequence. Among the T2-weighted images, the highest CNR and the best image quality were obtained with the UTSE sequence, followed by the fat-suppressed UTSE sequence. GraSE and conventional SE sequences showed a significantly lower CNR and image quality (p < 0.05). The T1-weighted sequences did not show significant differences, in either precontrast or postcontrast measurements. T2-weighted UTSE with and without fat suppression combined excellent image quality and high CNR for imaging and detection of renal lesions. The T1-weighted fast sequences provided no alternative to the gradient-echo or to the conventional SE sequences. The results of this systematic study suggest the use of T2-weighted fast techniques for improved diagnostic accuracy of renal MRI.