Dynamic MR based analysis of tumor movement in upper and mid lobe localized lung cancer

Automatic tracking of the respiratory motion of lung parenchyma on dynamic magnetic resonance imaging: comparison with pulmonary function tests in patients with chronic obstructive pulmonary disease

PURPOSE

This study evaluated the respiratory motion of the lung parenchyma using dynamic magnetic resonance imaging and clarified differences between healthy individuals and patients with chronic obstructive pulmonary disease (COPD).

MATERIALS AND METHODS

The study comprised 6 healthy volunteers and 42 patients diagnosed with smoking-related COPD. We captured 80 sequential frames from the mid-sagittal portion of the right lung while repeating forced deep breathing using a balanced fast-field echo sequence (repetition time, 2.2 ms; echo time, 1.1 ms; slice thickness, 10 mm; field of view, 450 mm; matrix size, 128 × 256; and acquisition time, 0.28 s/frame). We traced 15 points on pulmonary vessels using a computer-aided system and measured the maximal motion distance of each tracked point. Movement of these points was then compared with spirometric data using the Pearson correlation coefficient.

RESULTS

Patients with COPD showed reduced respiratory motion compared with healthy volunteers. Respiratory motion and spirometric data such as forced expiratory volume in 1 s (FEV1) and FEV1/forced vital capacity showed highly significant positive correlations (correlation between normalized motion distance for the whole lung and FEV1, r = 0.75; P < 0.01).

CONCLUSIONS

The respiratory motion of the pulmonary vessels reflects expansion and deflation of the lung parenchyma, and such motion is restricted in patients with COPD due to airflow limitation.

The potential for an enhanced role for MRI in radiation-therapy treatment planning

The exquisite soft-tissue contrast of magnetic resonance imaging (MRI) has meant that the technique is having an increasing role in contouring the gross tumor volume (GTV) and organs at risk (OAR) in radiation therapy treatment planning systems (TPS). MRI-planning scans from diagnostic MRI scanners are currently incorporated into the planning process by being registered to CT data. The soft-tissue data from the MRI provides target outline guidance and the CT provides a solid geometric and electron density map for accurate dose calculation on the TPS computer. There is increasing interest in MRI machine placement in radiotherapy clinics as an adjunct to CT simulators. Most vendors now offer 70 cm bores with flat couch inserts and specialised RF coil designs. We would refer to these devices as MR-simulators. There is also research into the future application of MR-simulators independent of CT and as in-room image-guidance devices. It is within the background of this increased interest in the utility of MRI in radiotherapy treatment planning that this paper is couched. The paper outlines publications that deal with standard MRI sequences used in current clinical practice. It then discusses the potential for using processed functional diffusion maps (fDM) derived from diffusion weighted image sequences in tracking tumor activity and tumor recurrence. Next, this paper reviews publications that describe the use of MRI in patient-management applications that may, in turn, be relevant to radiotherapy treatment planning. The review briefly discusses the concepts behind functional techniques such as dynamic contrast enhanced (DCE), diffusion-weighted (DW) MRI sequences and magnetic resonance spectroscopic imaging (MRSI). Significant applications of MR are discussed in terms of the following treatment sites: brain, head and neck, breast, lung, prostate and cervix. While not yet routine, the use of apparent diffusion coefficient (ADC) map analysis indicates an exciting future application for functional MRI. Although DW-MRI has not yet been routinely used in boost adaptive techniques, it is being assessed in cohort studies for sub-volume boosting in prostate tumors.

Validation of SPAMM tagged MRI based measurement of 3D soft tissue deformation

PURPOSE

This study presents and validates a novel (non-ECG-triggered) MRI sequence based on spatial modulation of the magnetization (SPAMM) to noninvasively measure 3D (quasistatic) soft tissue deformations using only six acquisitions (three static and three indentations). In the current SPAMM tagged MRI approaches, data are typically constructed from many repeated motion cycles. This has so far restricted its application to the measurement of highly repeatable and periodic movements (e.g., cardiac deformation). In biomechanical applications where soft tissue deformation is artificially induced, often by indentation, significant repeatability constraints exist, and for clinical applications, discomfort and health issues generally preclude a large number of repetitions.

METHODS

A novel (non-ECG-triggered) SPAMM tagged MRI sequence is presented, whereby a single 1-1 (first order) SPAMM set is acquired following a 3D transient field echo acquisition. Full 3D deformation measurement is achieved through the combination of only six acquisitions (three static and three motion cycles). The 3D deformation measurements were validated using quasistatic indentation tests and marker tracking in a silicone gel soft tissue phantom. In addition, the technique's ability to measure 3D soft tissue deformation in vivo was evaluated using indentation of the biceps region of the upper arm in a volunteer.

RESULTS

Following comparison to marker tracking in the silicone gel phantom, the SPAMM tagged MRI based displacement measurement demonstrated subvoxel accuracy with a mean displacement difference of 72 microm and a standard deviation of 289 microm. In addition, precision of displacement magnitude was evaluated for both the phantom and the volunteer data. The standard deviations of the displacement magnitude with respect to the average displacement magnitude were 75 and 169 microm for the phantom and volunteer data, respectively.

CONCLUSIONS

The subvoxel accuracy and precision demonstrated in the phantom in combination with the precision comparison between the phantom and the volunteer data provide confidence in the methods presented for measurement of soft tissue deformation in vivo. To the author's knowledge, since only six acquisitions are required, the presented methodology is the fastest SPAMM tagged MRI method currently available for the noninvasive measurement of quasistatic 3D soft tissue deformation.