Sql-server – Query Optimization required – Subquery using Inner Join

Could anybody advise how can I optimize this query below please?

SELECT

IT.[iInternalTransactionID]
, IT.[iInternalAccountID]
, C.[iContractID]
, IT.[dtTransactionDate] AS TransactionDate
, (CL.[sFirstName] + ' ' + CL.[sLastName]) AS ClientName

...

-- ### I would like to optimize this by using inner join ##--
, (SELECT MAX(CPH.[iTermNo]) 
    FROM [tbl_ContractPaymentHistory] CPH
    WHERE CPH.[iContractID] = C.[iContractID]
    AND CPH.[iInternalAccountID] = @InternalAccountID
    AND CPH.[dtTransactionDate] = IT.[dtTransactionDate])  AS TermNo

, (SELECT (MAX(CPH.[iTermNo])  * MAX(CPH.[cMonthlyAmount]))
    FROM [tbl_ContractPaymentHistory] CPH
    WHERE CPH.[iContractID] = C.[iContractID]
    AND CPH.[iInternalAccountID] = @InternalAccountID
    AND CPH.[dtTransactionDate] = IT.[dtTransactionDate])  AS TotalAmount
-- ### end ### --
...

FROM 
    [tbl_InternalTransactions] IT
    INNER JOIN [tbl_Contract] C ON C.[iContractID] = IT.[iContractID]
    INNER JOIN [tbl_Client] CL ON CL.[iClientID] = C.[iClientID]
    INNER JOIN [tbl_FinanceStructure] FS ON FS.[iFinanceStructureID] = C.[iFinanceStructureID]
    INNER JOIN [tbl_InternalAccount] IA ON IT.[iInternalAccountID] = IA.[iInternalAccountID]
    AND IA.[iInternalAccountID] = @InternalAccountID
WHERE 
    IT.[dtTransactionDate] >= @FromDate
    AND IT.[dtTransactionDate] <= @ToDate

...

The query plan can be found here: http://pastebin.com/KHPdEzgi

I have tried to replace the subqueries with the following:

INNER JOIN ( 
SELECT 
    MAX([iContractID]) AS [iContractID] 
    , MAX([iTermNo]) AS [iTermNo] 
    , MAX([cMonthlyAmount]) AS [cMonthlyAmount]
FROM [tbl_ContractPaymentHistory] 
WHERE [iInternalAccountID] = @InternalAccountID
    AND [dtTransactionDate] = IT.[dtTransactionDate] -- not able to use this here
    AND [iContractID] = C.[iContractID]          -- not able to use this here
        ) CPH ON CPH.[iContractID] = C.[iContractID]

So I can select [iTermNo] and [cMonthlyAmount]

However, I am not able to use columns from another tables in the inner join subquery. I am getting the following errors:
The multi-part identifier "IT.dtTransactionDate" could not be bound.
The multi-part identifier "C.[iContractID]" could not be bound.

Help would be much appreciated as the query takes an eternity to load at the moment. Thank you.