Accelerated T2 mapping for characterization of prostate cancer

Abstract

Prostate T(2) mapping was performed in 34 consecutive patients using an accelerated multiecho spin-echo sequence with 4-fold k-space undersampling leading to a net acceleration factor of 3.3 on a 3T scanner. The mean T(2) values from the accelerated and conventional, unaccelerated sequences demonstrated a very high correlation (r = 0.99). Different prostate segments demonstrated similarly good interscan reproducibility (p = not significant) with slightly larger difference at base: 2.0% ± 1.6% for left base and 2.1% ± 1.1% for right base. In patients with subsequent targeted biopsy, T(2) values of histologically proven malignant tumor areas were significantly lower than the suspicious looking but nonmalignant lesions (p < 0.05) and normal areas (p < 0.001): 100 ± 10 ms for malignant tumors, 114 ± 23 ms for suspicious lesions and 149 ± 32 ms for normal tissues. The proposed method can provide an effective approach for accelerated T(2) quantification for prostate patients.

Figure 1

Acquisition scheme for an undersampling factor R = 4. Black lines represent the acquired k-space samples. Blue lines represent the skipped sampling positions corresponding to Nyquist sampling. Red lines represent the samples acquired for autocalibration.

Figure 2

The reconstructed images at echo times 80 ms (a) and 160 ms (b) and the calculated T₂ map (c) from the reconstructed images from a patient (54 yrs, PSA = 3.6, Gleason 6 (3 +3)). Yellow arrows indicate a suspicious lesion.

Figure 3

T2 maps (a) acquired from the accelerated approach (R = 4) and the conventional unaccelerated approach (R =1) from a patient(59 yrs, PSA = 11.1), regression plot (b) and Bland-Altman plot (c) of the mean T₂ values obtained with the accelerated T₂ mapping technique and the conventional T₂ mapping. The mean T₂ values obtained with R = 4 demonstrated very good correlations (r = 0.99) with the mean T₂ values obtained with the conventional sequence. The Bland-Altman plot confirmed the very good agreement between the regular and accelerated measurements.

Figure 4

Interscan reproducibility of the fast T₂ mapping technique. All six segments demonstrated similarly good reproducibility (p = NS) with slightly larger difference at base: 2.0± 1.6 % for LB and 2.1 ± 1.1 % for RB.

Figure 5

Representative T₂ map (a) and the corresponding lesion targets for fused MRI/TRUS guided biopsy overlaid on the corresponding T₂ weighted image (b). Fused MR/TRUS guided biopsy targeted for these two lesions revealed a malignant tumor of Gleason 7 (3 + 4) for the left lesion and a malignant tumor of Gleason 6 (3 + 3) for the right lesion. These two lesions were conspicuous on the T₂ map (a) with T₂ of 95 ± 7 ms for the right target and 97 ± 13 ms for the left target vs. 169 ± 17 ms for the right control and 272 ± 57 ms for the left control (c).

Figure 6

The T₂ values of malignant tumors were significantly lower than the control regions: 100 ± 10 ms for malignant tumors vs. 149 ± 32 ms for controls (p< 0.001). The T₂ values of suspicious regions (with negative biopsy) were also lower than the controls: 114 ± 23 ms for suspicious regions vs. 153 ± 34 ms for controls (p<0.001). Compared to malignant tumor areas, the suspicious areas demonstrated higher T₂ values (p<0.05) while the control areas from both groups were statistically equivalent (p =NS).