  Pulsar radio emission undergoes dispersion due to the presence of free
electrons in the interstellar medium (ISM). The dispersive delay in the arrival
time of pulsar signal changes over time due to the varying ISM electron column
density along the line of sight. Correcting for this delay accurately is
crucial for the detection of nanohertz gravitational waves using Pulsar Timing
Arrays. In this work, we present in-band and inter-band DM estimates of four
pulsars observed with uGMRT over the timescale of a year using two different
template alignment methods. The DMs obtained using both these methods show only
subtle differences for PSR 1713+0747 and J1909$-$3744. A considerable offset is
seen in the DM of PSR J1939+2134 and J2145$-$0750 between the two methods. This
could be due to the presence of scattering in the former and profile evolution
in the latter. We find that both methods are useful but could have a systematic
offset between the DMs obtained. Irrespective of the template alignment methods
followed, the precision on the DMs obtained is about $10^{-3}$ pc cm$^{-3}$
using only BAND3 and $10^{-4}$ pc cm$^{-3}$ after combining data from BAND3 and
BAND5 of the uGMRT. In a particular result, we have detected a DM excess of
about $5\times10^{-3}$ pc cm$^{-3}$ on 24 February 2019 for PSR J2145$-$0750.
This excess appears to be due to the interaction region created by fast solar
wind from a coronal hole and a coronal mass ejection (CME) observed from the
Sun on that epoch. A detailed analysis of this interesting event is presented.
